I am running GDB 10.1 on x86_64 GNU/Linux targeting ARM. While debugging a core file with "-i=mi" and repeatedly running e.g. "-stack-list-variables --thread 1 --frame 0 --simple-values" results in a segmentation fault. The first call returns "frame" and "variables" information. The second call returns just the "variables". The third call segfaults in "follow_die_offset" (dwarf2/read.c:22950). The segfaulting line reads: target_cu->ancestor = cu; target_cu is apparently 0. I can reproduce the issue with current master (e1f57067b162cba9f39e087726c7a2f2cfaae96f) too. With GDB 9.1 the third (and subsequent) calls don't seem to segfault.
Hi Nils, Can you provide some files to reproduce the issue? Otherwise it's not really possible to look into it. Simon
Hello Simon, thank you for looking into this. "git bisect" tells me the issue might exist since: 17ee85fc2af74471e8c57502714a32bbeac5f1ae "Share DWARF partial symtabs" I don't have any reasonably shareable files yet. I'll try to construct / reduce a test case somehow but I don't know how long that'll take or how succesfull I'll be; not even entirely sure how I'll go about constructing one yet.
Ok, thanks. The problematic commit is one I worked on, so I'll take a look once you upload a reproducer.
Created attachment 12941 [details] reproducer I've attached an archive with a test case that reproduces the issue for me. It contains an executable (Foo), core-file (Foo-core), libpthread.so.0 from the arm target system and a shell script (repo.sh) that runs arm-linux-gnueabi-gdb with a sequence of commands that reproduces the crash on my system(s). I had to increase the number of queries to trigger the segmentation fault but am hoping the test case is still deterministic and does not depend on anything else specific to my system.
Whatever I do, I can't get a backtrace using your core. I always get a variation of: (gdb) bt #0 0xb6c3809c in pthread_mutex_trylock () from /lib/libpthread.so.0 Backtrace stopped: Cannot access memory at address 0x120 I'm guessing that in your development sysroot, you have debug info for /lib/libpthread.so.0, and that makes GDB able to unwind the frames in that library. It's probably a separate debug file. Can you check, and if so, provide it?
Actually, I made some progress. The solib-search-path isn't sufficient, I think GDB opens /lib/libpthread.so.0 on my system. It would be more appropriate to use "set sysroot" in this situation. When setting the sysroot, to the base of what you provided, then the correct /lib/libpthread.so.0 is loaded by GDB. Another note for those trying to reproduce: if you have a --enable-targets=all GDB, it will (erroneously) detect the core as having the Symbian osabi and then tell you that it doesn't know how to handle cores. Use "set osabi GNU/Linux" to force it to use that osabi. So now the status is that I do get a crash, but I think it's not the same as you, I think it's earlier. I build with --enable-ubsan, and that looks like an undefined behabior sanitizer message $ ../gdb -nx --data-directory=../data-directory (gdb) set osabi GNU/Linux (gdb) set sysroot /home/simark/build/binutils-gdb/gdb/repo (gdb) file Foo Reading symbols from Foo... (gdb) core-file Foo-core warning: Can't open file /media/mmcblk0p1/install/usr/bin/Foo during file-backed mapping note processing warning: Can't open file /lib/libm-2.21.so during file-backed mapping note processing warning: Can't open file /lib/libpthread-2.21.so during file-backed mapping note processing warning: Can't open file /lib/libgcc_s.so.1 during file-backed mapping note processing warning: Can't open file /media/mmcblk0p1/install/usr/lib/libstdc++.so.6 during file-backed mapping note processing warning: Can't open file /lib/libc-2.21.so during file-backed mapping note processing warning: Can't open file /lib/ld-2.21.so during file-backed mapping note processing [New LWP 29367] [New LWP 29368] warning: Could not load shared library symbols for 5 libraries, e.g. /lib/libc.so.6. Use the "info sharedlibrary" command to see the complete listing. Do you need "set solib-search-path" or "set sysroot"? warning: Unable to find libthread_db matching inferior's thread library, thread debugging will not be available. warning: Unable to find libthread_db matching inferior's thread library, thread debugging will not be available. Core was generated by `./Foo'. Program terminated with signal SIGABRT, Aborted. #0 0xb6c3809c in pthread_cond_wait () from /home/simark/build/binutils-gdb/gdb/repo/lib/libpthread.so.0 [Current thread is 1 (LWP 29367)] (gdb) bt /home/simark/src/binutils-gdb/gdb/arm-tdep.c:1551:30: runtime error: shift exponent 32 is too large for 32-bit type 'unsigned int'
I fixed the undefined shift behavior problem, and was able to reproduce your problem. This is the command line you provided that I adapted: ../gdb -nx --data-directory=../data-directory -i mi Foo <<EOF set sysroot /home/simark/build/binutils-gdb/gdb/repo set osabi GNU/Linux core-file Foo-core -stack-list-variables --thread 2 --frame 2 --simple-values -stack-list-variables --thread 2 --frame 2 --simple-values -stack-list-variables --thread 2 --frame 2 --simple-values -stack-list-variables --thread 2 --frame 2 --simple-values -stack-list-variables --thread 2 --frame 2 --simple-values -stack-list-variables --thread 2 --frame 2 --simple-values EOF This is what I get: $ ./repo.sh warning: Found custom handler for signal 7 (Bus error) preinstalled. warning: Found custom handler for signal 8 (Floating point exception) preinstalled. warning: Found custom handler for signal 11 (Segmentation fault) preinstalled. Some signal dispositions inherited from the environment (SIG_DFL/SIG_IGN) won't be propagated to spawned programs. =thread-group-added,id="i1" ~"GNU gdb (GDB) 11.0.50.20201103-git\n" ~"Copyright (C) 2020 Free Software Foundation, Inc.\n" ~"License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>\nThis is free software: you are free to change and redistribute it.\nThere is NO WARRANTY, to the extent permitted by law." ~"\nType \"show copying\" and \"show warranty\" for details.\n" ~"This GDB was configured as \"x86_64-pc-linux-gnu\".\n" ~"Type \"show configuration\" for configuration details.\n" ~"For bug reporting instructions, please see:\n" ~"<https://www.gnu.org/software/gdb/bugs/>.\n" ~"Find the GDB manual and other documentation resources online at:\n <http://www.gnu.org/software/gdb/documentation/>." ~"\n\n" ~"For help, type \"help\".\n" ~"Type \"apropos word\" to search for commands related to \"word\"...\n" ~"Reading symbols from Foo...\n" (gdb) &"set sysroot /home/simark/build/binutils-gdb/gdb/repo\n" =cmd-param-changed,param="sysroot",value="/home/simark/build/binutils-gdb/gdb/repo" ^done (gdb) &"set osabi GNU/Linux\n" =cmd-param-changed,param="osabi",value="GNU/Linux" ^done (gdb) &"core-file Foo-core\n" &"warning: Can't open file /media/mmcblk0p1/install/usr/bin/Foo during file-backed mapping note processing\n" &"warning: Can't open file /lib/libm-2.21.so during file-backed mapping note processing\n" &"warning: Can't open file /lib/libpthread-2.21.so during file-backed mapping note processing\n" &"warning: Can't open file /lib/libgcc_s.so.1 during file-backed mapping note processing\n" &"warning: Can't open file /media/mmcblk0p1/install/usr/lib/libstdc++.so.6 during file-backed mapping note processing\n" &"warning: Can't open file /lib/libc-2.21.so during file-backed mapping note processing\n" &"warning: Can't open file /lib/ld-2.21.so during file-backed mapping note processing\n" =thread-group-started,id="i1",pid="29367" =thread-created,id="1",group-id="i1" ~"[New LWP 29367]\n" =thread-created,id="2",group-id="i1" ~"[New LWP 29368]\n" =library-loaded,id="/lib/libc.so.6",target-name="/lib/libc.so.6",host-name="/lib/libc.so.6",symbols-loaded="0",thread-group="i1",ranges=[{}] =library-loaded,id="/media/mmcblk0p1/install/usr/bin/../lib/libstdc++.so.6",target-name="/media/mmcblk0p1/install/usr/bin/../lib/libstdc++.so.6",host-name="/media/mmcblk0p1/install/usr/bin/../lib/libstdc++.so.6",symbols-loaded="0",thread-group="i1",ranges=[{}] =library-loaded,id="/lib/libgcc_s.so.1",target-name="/lib/libgcc_s.so.1",host-name="/lib/libgcc_s.so.1",symbols-loaded="0",thread-group="i1",ranges=[{}] =library-loaded,id="/lib/libpthread.so.0",target-name="/lib/libpthread.so.0",host-name="/home/simark/build/binutils-gdb/gdb/repo/lib/libpthread.so.0",symbols-loaded="0",thread-group="i1",ranges=[{from="0xb6c30160",to="0xb6c3ec88"}] =library-loaded,id="/lib/ld-linux.so.3",target-name="/lib/ld-linux.so.3",host-name="/lib/ld-linux.so.3",symbols-loaded="0",thread-group="i1",ranges=[{}] =library-loaded,id="/lib/libm.so.6",target-name="/lib/libm.so.6",host-name="/lib/libm.so.6",symbols-loaded="0",thread-group="i1",ranges=[{}] &"warning: Could not load shared library symbols for 5 libraries, e.g. /lib/libc.so.6.\nUse the \"info sharedlibrary\" command to see the complete listing.\nDo you need \"set solib-search-path\" or \"set sysroot\"?" &"\n" &"warning: Unable to find libthread_db matching inferior's thread library, thread debugging will not be available.\n" &"warning: Unable to find libthread_db matching inferior's thread library, thread debugging will not be available.\n" ~"Core was generated by `./Foo'.\n" ~"Program terminated with signal SIGABRT, Aborted.\n" ~"#0 0xb6c3809c in pthread_cond_wait () from /home/simark/build/binutils-gdb/gdb/repo/lib/libpthread.so.0\n" ~"[Current thread is 1 (LWP 29367)]\n" ^done (gdb) ^done,variables=[{name="lock",arg="1",type="boost::asio::detail::conditionally_enabled_mutex::scoped_lock &",value="<synthetic pointer>: {<boost::asio::detail::noncopyable> = {<No data fields>}, mutex_ = @0x2cf50, locked_ = true}"},{name="this",arg="1",type="boost::asio::detail::conditionally_enabled_event * const",value="0x2cf70"}] (gdb) ^done,variables=[{name="lock",arg="1",type="boost::asio::detail::conditionally_enabled_mutex::scoped_lock &",value="<synthetic pointer>: {<boost::asio::detail::noncopyable> = {<No data fields>}, mutex_ = @0x2cf50, locked_ = true}"},{name="this",arg="1",type="boost::asio::detail::conditionally_enabled_event * const",value="0x2cf70"}] (gdb) ^done,variables=[{name="lock",arg="1",type="boost::asio::detail::conditionally_enabled_mutex::scoped_lock &",value="<synthetic pointer>: {<boost::asio::detail::noncopyable> = {<No data fields>}, mutex_ = @0x2cf50, locked_ = true}"},{name="this",arg="1",type="boost::asio::detail::conditionally_enabled_event * const",value="0x2cf70"}] (gdb) ^done,variables=[{name="lock",arg="1",type="boost::asio::detail::conditionally_enabled_mutex::scoped_lock &",value="<synthetic pointer>: {<boost::asio::detail::noncopyable> = {<No data fields>}, mutex_ = @0x2cf50, locked_ = true}"},{name="this",arg="1",type="boost::asio::detail::conditionally_enabled_event * const",value="0x2cf70"}] (gdb) ^done,variables=[{name="lock",arg="1",type="boost::asio::detail::conditionally_enabled_mutex::scoped_lock &",value="<synthetic pointer>: {<boost::asio::detail::noncopyable> = {<No data fields>}, mutex_ = @0x2cf50, locked_ = true}"},{name="this",arg="1",type="boost::asio::detail::conditionally_enabled_event * const",value="0x2cf70"}] (gdb) /home/simark/src/binutils-gdb/gdb/dwarf2/read.c:22959:25: runtime error: member access within null pointer of type 'struct dwarf2_cu'
Thank you for putting in the extra work in getting this to reproduce. Quite relieved that it isn't only reproducible on my system. libpthread.so.0 is located elsewhere on my system which is why I presumably didn't trip there. Also didn't know about "--enable-targets=all" yet!
Nils, could you try the following patch? The issue lies with the fact that we have a DIE in a CU A referring to a DIE in a CU B (using DW_AT_abstract_origin). The DIEs for CU B are not loaded yet (or rather, have been unloaded due to DWARF CU aging stuff), and we try to load them using: /* If necessary, add it to the queue and load its DIEs. */ if (maybe_queue_comp_unit (cu, per_cu, per_objfile, cu->language)) load_full_comp_unit (per_cu, per_objfile, per_objfile->get_cu (per_cu), false, cu->language); Since the CU is already queued for expansion, maybe_queue_comp_unit returns false and we don't call load_full_comp_unit. I think maybe_queue_comp_unit is the wrong thing to call here, because "queuing for symtab expansion" is unrelated to "loading the DIEs in memory". We should rather check: "are the DIEs for per_cu loaded into memory yet? if not do it now", which is what the patch below implements. @@ -22937,12 +22939,15 @@ follow_die_offset (sect_offset sect_off, int offset_in_dwz, per_cu = dwarf2_find_containing_comp_unit (sect_off, offset_in_dwz, per_objfile); - /* If necessary, add it to the queue and load its DIEs. */ - if (maybe_queue_comp_unit (cu, per_cu, per_objfile, cu->language)) - load_full_comp_unit (per_cu, per_objfile, per_objfile->get_cu (per_cu), - false, cu->language); - target_cu = per_objfile->get_cu (per_cu); + if (target_cu == nullptr) + { + load_full_comp_unit (per_cu, per_objfile, per_objfile->get_cu (per_cu), + false, cu->language); + target_cu = per_objfile->get_cu (per_cu); + } + + gdb_assert (target_cu != nullptr); } else if (cu->dies == NULL) {
While the attached test case now seems to pass my original case now fails with: ../../../../binutils-gdb/gdb/dwarf2/read.c:9251: internal-error: void load_full_comp_unit(dwarf2_per_cu_data*, dwarf2_per_objfile*, dwarf2_cu*, bool, language): Assertion `cu->die_hash == NULL' failed. A problem internal to GDB has been detected, further debugging may prove unreliable. Not sure if that means this is a related or an independent issue.
(In reply to Nils Gladitz from comment #10) > While the attached test case now seems to pass my original case now fails > with: > > ../../../../binutils-gdb/gdb/dwarf2/read.c:9251: internal-error: void > load_full_comp_unit(dwarf2_per_cu_data*, dwarf2_per_objfile*, dwarf2_cu*, > bool, language): Assertion `cu->die_hash == NULL' failed. > A problem internal to GDB has been detected, > further debugging may prove unreliable. > > Not sure if that means this is a related or an independent issue. It's possibly related. Is that load_full_comp_unit call the one I touched in the patch, or is it a later one? Could you provide the backtrace of this new assertion failure?
Looks like it comes from a different call: #0 __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50 #1 0x00007fc878bb0859 in __GI_abort () at abort.c:79 #2 0x000056229e1f0e76 in dump_core () at ../../../../binutils-gdb/gdb/utils.c:204 #3 0x000056229e1f1799 in internal_vproblem(internal_problem *, const char *, int, const char *, typedef __va_list_tag __va_list_tag *) (problem=0x56229f7c09e0 <internal_error_problem>, file=0x56229e7cb208 "../../../../binutils-gdb/gdb/dwarf2/read.c", line=9251, fmt=0x56229e7ca848 "%s: Assertion `%s' failed.", ap=0x7ffc18d82410) at ../../../../binutils-gdb/gdb/utils.c:414 #4 0x000056229e1f1890 in internal_verror ( file=0x56229e7cb208 "../../../../binutils-gdb/gdb/dwarf2/read.c", line=9251, fmt=0x56229e7ca848 "%s: Assertion `%s' failed.", ap=0x7ffc18d82410) at ../../../../binutils-gdb/gdb/utils.c:439 #5 0x000056229e685fda in internal_error ( file=0x56229e7cb208 "../../../../binutils-gdb/gdb/dwarf2/read.c", line=9251, fmt=0x56229e7ca848 "%s: Assertion `%s' failed.") at ../../../../binutils-gdb/gdbsupport/errors.cc:55 #6 0x000056229d7c1103 in load_full_comp_unit (this_cu=0x5622a1d2f220, per_objfile=0x5622a1351a10, existing_cu=0x5622b648d2f0, skip_partial=false, pretend_language=language_minimal) at ../../../../binutils-gdb/gdb/dwarf2/read.c:9251 #7 0x000056229d783f35 in load_cu (per_cu=0x5622a1d2f220, per_objfile=0x5622a1351a10, skip_partial=false) at ../../../../binutils-gdb/gdb/dwarf2/read.c:2389 #8 0x000056229d7840ad in dw2_do_instantiate_symtab (per_cu=0x5622a1d2f220, per_objfile=0x5622a1351a10, skip_partial=false) at ../../../../binutils-gdb/gdb/dwarf2/read.c:2420 #9 0x000056229d7c0926 in dwarf2_psymtab::expand_psymtab (this=0x5622a293efa0, objfile=0x5622a1d5f4b0) at ../../../../binutils-gdb/gdb/dwarf2/read.c:9183 #10 0x000056229d7bf853 in dwarf2_psymtab::read_symtab (this=0x5622a293efa0, objfile=0x5622a1d5f4b0) at ../../../../binutils-gdb/gdb/dwarf2/read.c:9031 in load_cu: else load_full_comp_unit (per_cu, per_objfile, per_objfile->get_cu (per_cu), skip_partial, language_minimal); dwarf2_cu *cu = per_objfile->get_cu (per_cu); if (cu == nullptr) return nullptr; /* Dummy CU. */
Yeah it looks like this is a consequence of my change. load_cu doesn't like that the CU was already loaded in memory. The obvious fix would be to make it skip the load if it already is loaded, see patch below. Although to be sure of what happens, I would need to be able to debug it myself, if you have a change to make a reproducer for this. diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c index 7d258f30eba7..150f54335433 100644 --- a/gdb/dwarf2/read.c +++ b/gdb/dwarf2/read.c @@ -2383,13 +2383,19 @@ static dwarf2_cu * load_cu (dwarf2_per_cu_data *per_cu, dwarf2_per_objfile *per_objfile, bool skip_partial) { - if (per_cu->is_debug_types) - load_full_type_unit (per_cu, per_objfile); - else - load_full_comp_unit (per_cu, per_objfile, per_objfile->get_cu (per_cu), - skip_partial, language_minimal); - dwarf2_cu *cu = per_objfile->get_cu (per_cu); + + if (cu == nullptr) + { + if (per_cu->is_debug_types) + load_full_type_unit (per_cu, per_objfile); + else + load_full_comp_unit (per_cu, per_objfile, per_objfile->get_cu (per_cu), + skip_partial, language_minimal); + + cu = per_objfile->get_cu (per_cu); + } + if (cu == nullptr) return nullptr; /* Dummy CU. */
Thanks, this does seem to fix the issue for me now! Is this sufficient feedback or do you still want a new reproducer for this? Creating the first one was quite time consuming (chiseling down a somewhat large project and continuously deploying to ARM) and I think I might have gotten somewhat lucky too. Unsure how much it'll take to create a new reproducer given that I don't understand how my core dumps are specifically triggering the first or the second issue or why this doesn't come up as an issue elsewhere (none of this CU loading / unloading stuff sounds like it would be ARM specific or in any sense rare?).
A reproducer is always preferable, because I wouldn't be comfortable committing a fix that I don't understand precisely and can't explain, but I understand if you don't have time.
Created attachment 12947 [details] second reproducer
I've attached a second test case that reproduces both issues for me (i.e. does not pass with just the first patch applied).
Awesome, thanks. I'll take a look when I have a bit of free time.
Ok, I think I was able to reproduce: ~"/home/simark/src/binutils-gdb/gdb/dwarf2/read.c:9255: internal-error: void load_full_comp_unit(dwarf2_per_cu_data*, dwarf2_per_objfile*, dwarf2_cu*, bool, language): Assertion `cu->die_hash == NULL' failed.\nA problem internal to GDB has been detected,\nfurther debugging may prove unreliable." ~"\nQuit this debugging session? " ~"(y or n) [answered Y; input not from terminal]\n" &"\nThis is a bug, please report it." &" For instructions, see:\n" &"<https://www.gnu.org/software/gdb/bugs/>.\n\n" ~"/home/simark/src/binutils-gdb/gdb/dwarf2/read.c:9255: internal-error: void load_full_comp_unit(dwarf2_per_cu_data*, dwarf2_per_objfile*, dwarf2_cu*, bool, language): Assertion `cu->die_hash == NULL' failed.\nA problem internal to GDB has been detected,\nfurther debugging may prove unreliable." ~"\nCreate a core file of GDB? " ~"(y or n) [answered Y; input not from terminal]\n"
The master branch has been updated by Simon Marchi <simark@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=9ecab40c77fd414fe408967d0f92f00494aa11b9 commit 9ecab40c77fd414fe408967d0f92f00494aa11b9 Author: Simon Marchi <simon.marchi@polymtl.ca> Date: Fri Nov 13 11:58:37 2020 -0500 gdb/arm: avoid undefined behavior shift when decoding immediate value When loading the code file provided in PR 26828 and GDB is build with UBSan, we get: Core was generated by `./Foo'. Program terminated with signal SIGABRT, Aborted. #0 0xb6c3809c in pthread_cond_wait () from /home/simark/build/binutils-gdb/gdb/repo/lib/libpthread.so.0 [Current thread is 1 (LWP 29367)] (gdb) bt /home/simark/src/binutils-gdb/gdb/arm-tdep.c:1551:30: runtime error: shift exponent 32 is too large for 32-bit type 'unsigned int' The sequence of instructions at pthread_cond_wait, in the libpthread.so.0 library, contains this instruction with an immediate constant with a "rotate amount" of 0: e24dd044 sub sp, sp, #68 ; 0x44 Since arm_analyze_prologue shifts by "32 - rotate amount", it does a 32 bit shift of a 32 bit type, which is caught by UBSan. Fix it by factoring out the decoding of immediates in a new function, arm_expand_immediate. I added a selftest for arm_analyze_prologue that replicates the instruction sequence. Without the fix, it crashes GDB if it is build with --enable-ubsan. I initially wanted to re-use the abstract_memory_reader class already in arm-tdep.c, used to make arm_process_record testable. However, arm_process_record and arm_analyze_prologue don't use the same kind of memory reading functions. arm_process_record uses a function that returns an error status on failure while arm_analyze_prologue uses one that throws an exception. Since i didn't want to introduce any other behavior change, I decided to just introduce a separate interface (arm_instruction_reader). It is derived from abstract_instruction_reader in aarch64-tdep.c. gdb/ChangeLog: PR gdb/26835 * arm-tdep.c (class arm_instruction_reader): New. (target_arm_instruction_reader): New. (arm_analyze_prologue): Add instruction reader parameter and use it. Use arm_expand_immediate. (class target_arm_instruction_reader): Adjust. (arm_skip_prologue): Adjust. (arm_expand_immediate): New. (arm_scan_prologue): Adjust. (arm_analyze_prologue_test): New. (class test_arm_instruction_reader): New. Change-Id: Ieb1c1799bd66f8c7421384f44f5c2777b578ff8d
Created attachment 12955 [details] Proposed patch series Hi Nils, Can you try this patch series see if it's good on your side? On my side, the second reproducer you sent works correctly, and I see no regression in GDB's testsuite. The previous patchlets that I asked you to try were not correct, as they broke other things. I am based on commit 9ecab40c77fd414fe408967d0f92f00494aa11b9. The series.patch file contains all 4 patches, you can apply them with $ git am series.patch The series breaks some things in the middle only to fix them in the last patch, so in the end I will probably re-order them, but the end result will be the same.
Works for me, thanks!
Series posted here: https://sourceware.org/pipermail/gdb-patches/2020-November/173372.html
The master branch has been updated by Simon Marchi <simark@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=de53369b2efcae78adf431437cb096c5a0728f96 commit de53369b2efcae78adf431437cb096c5a0728f96 Author: Simon Marchi <simon.marchi@polymtl.ca> Date: Wed Jan 20 21:04:43 2021 -0500 gdb/dwarf: add assertion in maybe_queue_comp_unit The symptom that leads to this is the crash described in PR 26828: /home/simark/src/binutils-gdb/gdb/dwarf2/read.c:23478:25: runtime error: member access within null pointer of type 'struct dwarf2_cu' The line of the crash is the following, in follow_die_offset: if (target_cu != cu) target_cu->ancestor = cu; <--- HERE The line that assign nullptr to `target_cu` is the `per_objfile->get_cu` call after having called maybe_queue_comp_unit: /* If necessary, add it to the queue and load its DIEs. */ if (maybe_queue_comp_unit (cu, per_cu, per_objfile, cu->language)) load_full_comp_unit (per_cu, per_objfile, per_objfile->get_cu (per_cu), false, cu->language); target_cu = per_objfile->get_cu (per_cu); <--- HERE Some background: there is an invariant, documented in maybe_queue_comp_unit's doc, that if a CU is queued for expansion (present in dwarf2_per_bfd::queue), then its DIEs are loaded in memory. "its DIEs are loaded in memory" is a synonym for saying that a dwarf2_cu object exists for this CU. Yet another way to say it is that `per_objfile->get_cu (per_cu)` returns something not nullptr for that CU. The crash documented in PR 26828 triggers some hard-to-reproduce sequence that ends up violating the invariant: - dwarf2_fetch_die_type_sect_off gets called for a DIE in CU A - The DIE in CU A requires some DIE in CU B - follow_die_offset calls maybe_queue_comp_unit. maybe_queue_comp_unit sees CU B is not queued and its DIEs are not loaded, so it enqueues it and returns 1 to its caller - meaning "the DIEs are not loaded, you should load them" - prompting follow_die_offset to load the DIEs by calling load_full_comp_unit - Note that CU B is enqueued by maybe_queue_comp_unit even if it has already been expanded. It's a bit useless (and causes trouble, see next patch), but that's how it works right now. - Since we entered the dwarf2/read code through dwarf2_fetch_die_type_sect_off, nothing processes the queue, so we exit the dwarf2/read code with CU B still lingering in the queue. - dwarf2_fetch_die_type_sect_off gets called for a DIE in CU A, again - The DIE in CU A requires some DIE in CU B, again - This time, maybe_queue_comp_unit sees that CU B is in the queue. Because of the invariant that if a CU is in the queue, its DIEs are loaded in the memory, it returns 0 to its caller, meaning "you don't need to load the DIEs!". - That happens to be true, so everything is fine for now. - Time passes, some things call dwarf2_per_objfile::age_comp_units enough so that CU B's age becomes past the dwarf_max_cache_age threshold. age_comp_units proceeds to free CU B's DIEs. Remember that CU B is still lingering in the queue (oops, the invariant just got violated). - dwarf2_fetch_die_type_sect_off gets called for a DIE in CU A, again - The DIE in CU A requires some DIE in CU B, again - maybe_queue_comp_unit sees that CU B is in the queue, so returns to its caller "you don't need to load the DIEs!". However, we know at this point this is false. - follow_die_offset doesn't load the DIEs and tries to obtain the DIEs for CU B: target_cu = per_objfile->get_cu (per_cu); But since they are not loaded, target_cu is nullptr, and we get the crash mentioned above a few lines after that. This patch adds an assertions in maybe_queue_comp_unit to verify the invariant, to make sure it doesn't return a falsehood to its caller. The current patch doesn't fix the issue (the next patch does), but it makes it so we catch the problem earlier and get this assertion failure instead of a segmentation fault: /home/simark/src/binutils-gdb/gdb/dwarf2/read.c:9100: internal-error: int maybe_queue_comp_unit(dwarf2_cu*, dwarf2_per_cu_data*, dwarf2_per_objfile*, language): Assertion `per_objfile->get_cu (per_cu) != nullptr' failed. gdb/ChangeLog: PR gdb/26828 * dwarf2/read.c (maybe_queue_comp_unit): Add assertion. Change-Id: I4e51bd7bd58773f9fadf480179cbc4bae61508fe
I have a pair of new core dumps, should they be useful: gdb coredump: https://www.dropbox.com/s/95p12ot0c0ya0l2/core.gdb.1000.32f860ba566941c786efd4ac4c070fb2.4549.1613756314000000.zst?dl=0 gnote coredump: https://www.dropbox.com/s/7a9v9x2x4bl3ksm/core.gnote.1000.0148951bf12149deab85f35229f2233e.108686.1613752706000000.zst?dl=0
(In reply to Davide Repetto from comment #25) > I have a pair of new core dumps, should they be useful: > > gdb coredump: > https://www.dropbox.com/s/95p12ot0c0ya0l2/core.gdb.1000. > 32f860ba566941c786efd4ac4c070fb2.4549.1613756314000000.zst?dl=0 > > gnote coredump: > https://www.dropbox.com/s/7a9v9x2x4bl3ksm/core.gnote.1000. > 0148951bf12149deab85f35229f2233e.108686.1613752706000000.zst?dl=0 Thanks. I think the bug will be fixed with the series I posted here (which is pending review): https://sourceware.org/pipermail/gdb-patches/2020-November/173372.html Is there a chance you can test it against your use case? If you have trouble applying patches, I can provide a git branch containing the change.
The master branch has been updated by Simon Marchi <simark@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=616c069a3f1a841e5bc63d20aec8e5b71b499f6c commit 616c069a3f1a841e5bc63d20aec8e5b71b499f6c Author: Simon Marchi <simon.marchi@polymtl.ca> Date: Tue Feb 23 12:07:10 2021 -0500 gdb/dwarf: don't enqueue CU in maybe_queue_comp_unit if already expanded The previous commit log described how items could be left lingering in the dwarf2_per_bfd::queue and how that could cause trouble. This patch fixes the issue by changing maybe_queue_comp_unit so that it doesn't put a CU in the to-expand queue if that CU is already expanded. This will make it so that when dwarf2_fetch_die_type_sect_off calls follow_die_offset and maybe_queue_comp_unit, it won't enqueue the target CU, because it will see the CU is already expanded. This assumes that if a CU is dwarf2_fetch_die_type_sect_off's target CU, it will have previously been expanded. I think it is the case, but I can't be 100% sure. If that's not true, the assertions added in the following patch will catch it, and it means we'll have to re-think a bit more how things work (it wouldn't be well handled at all today anyway). This fixes something else in maybe_queue_comp_unit that looks wrong. Imagine the DIEs of a CU are loaded in memory, but that CU is not expanded. In that case, maybe_queue_comp_unit will use this early return: /* If the compilation unit is already loaded, just mark it as used. */ dwarf2_cu *cu = per_objfile->get_cu (per_cu); if (cu != nullptr) { cu->last_used = 0; return 0; } ... so the CU won't be queued for expansion. Whether the DIEs of a CU are loaded in memory and whether that CU is expanded are two orthogonal things, but that function appears to mix them. So, move the queuing above that check / early return, so that if the CU's DIEs are loaded in memory but the CU is not expanded yet, it gets enqueued. I tried to improve maybe_queue_comp_unit's documentation to clarify what the return value means. By clarifying this, I noticed that two callers (follow_die_offset and follow_die_sig_1) access the CU's DIEs after calling maybe_queue_comp_unit, only relying on maybe_queue_comp_unit's return value to tell whether DIEs need to be loaded first or not. As explained in the new comment, this is problematic: maybe_queue_comp_unit's return value doesn't tell whether DIEs are currently loaded, it means whether maybe_queue_comp_unit requires the caller to load them. If the CU is already expanded but the DIEs to have been freed, maybe_queue_comp_unit returns 0, meaning "I don't need you to load the DIEs". So if these two functions (follow_die_offset and follow_die_sig_1) need to access the DIEs in any case, for their own usage, they should make sure to load them if they are not loaded already. I therefore added an extra check to the condition they use, making it so they will always load the DIEs if they aren't already. From what I found, other callers don't care for the CU's DIEs, they call maybe_queue_comp_unit to ensure the CU gets expanded eventually, but don't care for it after that. gdb/ChangeLog: PR gdb/26828 * dwarf2/read.c (maybe_queue_comp_unit): Check if CU is expanded to decide whether or not to enqueue it for expansion. (follow_die_offset, follow_die_sig_1): Ensure we load the DIEs after calling maybe_queue_comp_unit. Change-Id: Id98c6b60669f4b4b21b9be16d0518fc62bdf686a
The master branch has been updated by Simon Marchi <simark@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=08ac57714cd20e528efe9b4e169f3a2778cf6e30 commit 08ac57714cd20e528efe9b4e169f3a2778cf6e30 Author: Simon Marchi <simon.marchi@polymtl.ca> Date: Tue Feb 23 13:37:44 2021 -0500 gdb/dwarf: create and destroy dwarf2_per_bfd's CUs-to-expand queue As described in the log of patch "gdb/dwarf: add assertion in maybe_queue_comp_unit", it would happen that a call to maybe_queue_comp_unit would enqueue a CU in the to-expand queue while nothing up the stack was processing the queue. This is not desirable, as items are then left lingering in the queue when we exit the dwarf2/read code. This is an inconsistent state. The normal case of using the queue is when we go through dw2_do_instantiate_symtab and process_queue. As depended-on CUs are found, they get added to the queue. process_queue expands CUs until the queue is empty. To catch these cases where things are enqueued while nothing up the stack is processing the queue, change dwarf2_per_bfd::queue to be an optional. The optional is instantiated in dwarf2_queue_guard, just before where we call process_queue. In the dwarf2_queue_guard destructor, the optional gets reset. Therefore, the queue object is instantiated only when something up the stack is handling it. If another entry point tries to enqueue a CU for expansion, an assertion will fail and we know we have something to fix. dwarf2_queue_guard sounds like the good place for this, as it's currently responsible for making sure the queue gets cleared if we exit due to an error. This also allows asserting that when age_comp_units or remove_all_cus run, the queue is not instantiated, and gives us one more level of assurance that we won't free the DIEs of a CU that is in the CUs-to-expand queue. gdb/ChangeLog: PR gdb/26828 * dwarf2/read.c (dwarf2_queue_guard) <dwarf2_queue_guard>: Instantiate queue. (~dwarf2_queue_guard): Clear queue. (queue_comp_unit): Assert that queue is instantiated. (process_queue): Adjust. * dwarf2/read.h (struct dwarf2_per_bfd) <queue>: Make optional. Change-Id: I8fe3d77845bb4ad3d309eac906acebe79d9f0a9d
The gdb-10-branch branch has been updated by Simon Marchi <simark@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=1c8a25b683c7ea9621b7fccf6c07630bd67f071f commit 1c8a25b683c7ea9621b7fccf6c07630bd67f071f Author: Simon Marchi <simon.marchi@polymtl.ca> Date: Tue Feb 23 12:07:10 2021 -0500 gdb/dwarf: don't enqueue CU in maybe_queue_comp_unit if already expanded The previous commit log described how items could be left lingering in the dwarf2_per_bfd::queue and how that could cause trouble. This patch fixes the issue by changing maybe_queue_comp_unit so that it doesn't put a CU in the to-expand queue if that CU is already expanded. This will make it so that when dwarf2_fetch_die_type_sect_off calls follow_die_offset and maybe_queue_comp_unit, it won't enqueue the target CU, because it will see the CU is already expanded. This assumes that if a CU is dwarf2_fetch_die_type_sect_off's target CU, it will have previously been expanded. I think it is the case, but I can't be 100% sure. If that's not true, the assertions added in the following patch will catch it, and it means we'll have to re-think a bit more how things work (it wouldn't be well handled at all today anyway). This fixes something else in maybe_queue_comp_unit that looks wrong. Imagine the DIEs of a CU are loaded in memory, but that CU is not expanded. In that case, maybe_queue_comp_unit will use this early return: /* If the compilation unit is already loaded, just mark it as used. */ dwarf2_cu *cu = per_objfile->get_cu (per_cu); if (cu != nullptr) { cu->last_used = 0; return 0; } ... so the CU won't be queued for expansion. Whether the DIEs of a CU are loaded in memory and whether that CU is expanded are two orthogonal things, but that function appears to mix them. So, move the queuing above that check / early return, so that if the CU's DIEs are loaded in memory but the CU is not expanded yet, it gets enqueued. I tried to improve maybe_queue_comp_unit's documentation to clarify what the return value means. By clarifying this, I noticed that two callers (follow_die_offset and follow_die_sig_1) access the CU's DIEs after calling maybe_queue_comp_unit, only relying on maybe_queue_comp_unit's return value to tell whether DIEs need to be loaded first or not. As explained in the new comment, this is problematic: maybe_queue_comp_unit's return value doesn't tell whether DIEs are currently loaded, it means whether maybe_queue_comp_unit requires the caller to load them. If the CU is already expanded but the DIEs to have been freed, maybe_queue_comp_unit returns 0, meaning "I don't need you to load the DIEs". So if these two functions (follow_die_offset and follow_die_sig_1) need to access the DIEs in any case, for their own usage, they should make sure to load them if they are not loaded already. I therefore added an extra check to the condition they use, making it so they will always load the DIEs if they aren't already. From what I found, other callers don't care for the CU's DIEs, they call maybe_queue_comp_unit to ensure the CU gets expanded eventually, but don't care for it after that. gdb/ChangeLog: PR gdb/26828 * dwarf2/read.c (maybe_queue_comp_unit): Check if CU is expanded to decide whether or not to enqueue it for expansion. (follow_die_offset, follow_die_sig_1): Ensure we load the DIEs after calling maybe_queue_comp_unit. Change-Id: Id98c6b60669f4b4b21b9be16d0518fc62bdf686a
The gdb-10-branch branch has been updated by Simon Marchi <simark@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=ad4eb5acbab1b420b346236f2c8c272230477ab7 commit ad4eb5acbab1b420b346236f2c8c272230477ab7 Author: Simon Marchi <simon.marchi@polymtl.ca> Date: Tue Feb 23 13:37:44 2021 -0500 gdb/dwarf: create and destroy dwarf2_per_bfd's CUs-to-expand queue As described in the log of patch "gdb/dwarf: add assertion in maybe_queue_comp_unit", it would happen that a call to maybe_queue_comp_unit would enqueue a CU in the to-expand queue while nothing up the stack was processing the queue. This is not desirable, as items are then left lingering in the queue when we exit the dwarf2/read code. This is an inconsistent state. The normal case of using the queue is when we go through dw2_do_instantiate_symtab and process_queue. As depended-on CUs are found, they get added to the queue. process_queue expands CUs until the queue is empty. To catch these cases where things are enqueued while nothing up the stack is processing the queue, change dwarf2_per_bfd::queue to be an optional. The optional is instantiated in dwarf2_queue_guard, just before where we call process_queue. In the dwarf2_queue_guard destructor, the optional gets reset. Therefore, the queue object is instantiated only when something up the stack is handling it. If another entry point tries to enqueue a CU for expansion, an assertion will fail and we know we have something to fix. dwarf2_queue_guard sounds like the good place for this, as it's currently responsible for making sure the queue gets cleared if we exit due to an error. This also allows asserting that when age_comp_units or remove_all_cus run, the queue is not instantiated, and gives us one more level of assurance that we won't free the DIEs of a CU that is in the CUs-to-expand queue. gdb/ChangeLog: PR gdb/26828 * dwarf2/read.c (dwarf2_queue_guard) <dwarf2_queue_guard>: Instantiate queue. (~dwarf2_queue_guard): Clear queue. (queue_comp_unit): Assert that queue is instantiated. (process_queue): Adjust. * dwarf2/read.h (struct dwarf2_per_bfd) <queue>: Make optional. Change-Id: I8fe3d77845bb4ad3d309eac906acebe79d9f0a9d
This is hopefully fixed now.
The first call returns "frame" and "variables" information. The second call returns just the "variables". The third call segfaults in "follow_die_offset" (dwarf2/read.c:22950). The segfaulting line reads: target_cu->ancestor = cu; target_cu is apparently 0. I can reproduce the issue with current master (e1f57067b162cba9f39e087726c7a2f2cfaae96f) too. http://pitesti.online/ With GDB 9.1 the third (and subsequent) calls don't seem to segfault.
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ssibly similar to 23220 however on 64-bit recent Debian sid with trivial code I see : http://www-look-4.com/ mimas$ mimas$ uname -a http://www.compilatori.com/ Linux mimas 5.10.0-6-sparc64 #1 Debian 5.10.28-1 (2021-04-09) sparc64 GNU/Linux mimas$ http://www.wearelondonmade.com/ mimas$ mimas$ /usr/bin/gcc --version gcc (Debian 10.2.1-6) 10.2.1 20210110 http://www.jopspeech.com/ Copyright (C) 2020 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. http://joerg.li/ mimas$ mimas$ http://connstr.net/ mimas$ cat -n foo.c 1 2 #include <stdio.h> 3 #include <stdlib.h> 4 http://embermanchester.uk/ 5 int main(int argc, char **argv) 6 { 7 int a = 1; 8 http://www.slipstone.co.uk/ 9 printf("a = %i\n", a); 10 11 printf("&a = %p\n", &a); 12 13 return EXIT_SUCCESS; 14 http://www.logoarts.co.uk/ 15 } 16 mimas$ mimas$ http://www.acpirateradio.co.uk/ mimas$ /usr/bin/gcc -std=iso9899:1999 -pedantic -pedantic-errors -fno-builtin -g -m64 -O0 -mno-app-regs -mcpu=ultrasparc -mmemory-model=tso -o foo foo.c https://waytowhatsnext.com/ mimas$ debugging a core file with "-i=mi" and repeatedly running e.g. "-stack-list-variables --thread 1 --frame 0 --simple-values" results in a segmentation fault. https://www.webb-dev.co.uk/ The first call returns "frame" and "variables" information. The second call returns just the "variables". The third call segfaults in "follow_die_offset" (dwarf http://www.iu-bloomington.com/ The first call returns "frame" and "variables" information. The second call returns just the "variables". The third call segfaults in "follow_die_offset" (dwarf2/read.c:22950). The segfaulting line reads: target_cu->ancestor = cu; https://komiya-dental.com/ target_cu is apparent
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May I suggest removing the spam instead of hiding it? Hidden messages still give incentive. At a minimum, from the SEO perspective.
/home/simark/src/binutils-gdb/gdb/dwarf2/read.c:9100: internal-error: int maybe_queue_comp_unit(dwarf2_cu*, dwarf2_per_cu_data*, dwarf2_per_objfile*, language): Assertion `per_objfile->get_cu (per_cu) != nullptr' failed. https://www.crownfamilydentistry.com/ gdb/ChangeLog: PR gdb/26828 * dwarf2/read.c (maybe_queue_comp_unit): Add assertion. Change-Id: I4e51bd7bd58773f9fadf480179cbc4bae61508fe
$ ../gdb -nx --data-directory=../data-directory (gdb) set osabi GNU/Linux http://www.compilatori.com/category/technology/ (gdb) set sysroot /home/simark/build/binutils-gdb/gdb/repo (gdb) file Foo http://www.acpirateradio.co.uk/category/technology/ Reading symbols from Foo... (gdb) core-file Foo-core warning: Can't open file /media/mmcblk0p1/install/usr/bin/Foo during file-backed mapping note processing http://www.logoarts.co.uk/category/technology/ warning: Can't open file /lib/libm-2.21.so during file-backed mapping note processing warning: Can't open file /lib/libpthread-2.21.so during file-backed mapping note processing http://www.slipstone.co.uk/category/technology/ warning: Can't open file /lib/libgcc_s.so.1 during file-backed mapping note processing warning: Can't open file /media/mmcblk0p1/install/usr/lib/libstdc++.so.6 during file-backed mapping note processing http://embermanchester.uk/category/technology/ warning: Can't open file /lib/libc-2.21.so during file-backed mapping note processing warning: Can't open file /lib/ld-2.21.so during file-backed mapping note processing http://connstr.net/category/technology/ [New LWP 29367] [New LWP 29368] http://joerg.li/category/technology/ warning: Could not load shared library symbols for 5 libraries, e.g. /lib/libc.so.6. Use the "info sharedlibrary" command to see the complete listing. http://www.jopspeech.com/category/technology/ Do you need "set solib-search-path" or "set sysroot"? warning: Unable to find libthread_db matching inferior's thread library, thread debugging will not be available. http://www.wearelondonmade.com/category/technology/ warning: Unable to find libthread_db matching inferior's thread library, thread debugging will not be available. https://waytowhatsnext.com/category/shopping/ Core was generated by `./Foo'. Program terminated with signal SIGABRT, Aborted. http://www.iu-bloomington.com/category/shopping/ #0 0xb6c3809c in pthread_cond_wait () from /home/simark/build/binutils-gdb/gdb/repo/lib/libpthread.so.0 https://komiya-dental.com/category/shopping/ [Current thread is 1 (LWP 29367)] (gdb) bt http://www-look-4.com/category/technology/ /home/simark/src/binutils-gdb/gdb/arm-tdep.c:1551:30: runtime error: shift exponent 32 is too large for 32-bit type 'unsigned int' https://www.webb-dev.co.uk/category/shopping/
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