[PATCH v3] gdb: call check_typedef at beginning of dwarf_expr_context::fetch_result
Simon Marchi
simon.marchi@efficios.com
Thu Aug 18 17:34:18 GMT 2022
On 8/18/22 12:51, Luis Machado wrote:
> On 8/18/22 17:16, Simon Marchi via Gdb-patches wrote:
>> On 7/28/22 11:33, Simon Marchi wrote:
>>> From: Simon Marchi <simon.marchi@polymtl.ca>
>>>
>>> New in this version:
>>>
>>> - add architecture check in test
>>> - add aarch64 version of the .S
>>>
>>> Bug 29374 shows this crash:
>>>
>>> $ ./gdb -nx --data-directory=data-directory -q -batch -ex "catch throw" -ex r -ex bt a.out
>>> ...
>>> /home/simark/src/binutils-gdb/gdb/../gdbsupport/array-view.h:217: internal-error: copy: Assertion `dest.size () == src.size ()' failed.
>>>
>>> The backtrace is:
>>>
>>> #0 internal_error (file=0x5555606504c0 "/home/simark/src/binutils-gdb/gdb/../gdbsupport/array-view.h", line=217, fmt=0x55556064b700 "%s: Assertion `%s' failed.") at /home/simark/src/binutils-gdb/gdbsupport/errors.cc:51
>>> #1 0x000055555d41c0bb in gdb::copy<unsigned char const, unsigned char> (src=..., dest=...) at /home/simark/src/binutils-gdb/gdb/../gdbsupport/array-view.h:217
>>> #2 0x000055555deef28c in dwarf_expr_context::fetch_result (this=0x7fffffffb830, type=0x621007a86830, subobj_type=0x621007a86830, subobj_offset=0, as_lval=false) at /home/simark/src/binutils-gdb/gdb/dwarf2/expr.c:1040
>>> #3 0x000055555def0015 in dwarf_expr_context::evaluate (this=0x7fffffffb830, addr=0x62f00004313e "0", len=1, as_lval=false, per_cu=0x60b000069550, frame=0x621007c9e910, addr_info=0x0, type=0x621007a86830, subobj_type=0x621007a86830, subobj_offset=0) at /home/simark/src/binutils-gdb/gdb/dwarf2/expr.c:1091
>>> #4 0x000055555e084327 in dwarf2_evaluate_loc_desc_full (type=0x621007a86830, frame=0x621007c9e910, data=0x62f00004313e "0", size=1, per_cu=0x60b000069550, per_objfile=0x613000006080, subobj_type=0x621007a86830, subobj_byte_offset=0, as_lval=false) at /home/simark/src/binutils-gdb/gdb/dwarf2/loc.c:1485
>>> #5 0x000055555e0849e2 in dwarf2_evaluate_loc_desc (type=0x621007a86830, frame=0x621007c9e910, data=0x62f00004313e "0", size=1, per_cu=0x60b000069550, per_objfile=0x613000006080, as_lval=false) at /home/simark/src/binutils-gdb/gdb/dwarf2/loc.c:1529
>>> #6 0x000055555e0828c6 in dwarf_entry_parameter_to_value (parameter=0x621007a96e58, deref_size=0x0, type=0x621007a86830, caller_frame=0x621007c9e910, per_cu=0x60b000069550, per_objfile=0x613000006080) at /home/simark/src/binutils-gdb/gdb/dwarf2/loc.c:1235
>>> #7 0x000055555e082f55 in value_of_dwarf_reg_entry (type=0x621007a86890, frame=0x621007acc510, kind=CALL_SITE_PARAMETER_DWARF_REG, kind_u=...) at /home/simark/src/binutils-gdb/gdb/dwarf2/loc.c:1332
>>> #8 0x000055555e083449 in value_of_dwarf_block_entry (type=0x621007a86890, frame=0x621007acc510, block=0x61e000033568 "T\004\205\001\240\004\004\243\001T\237\004\240\004\261\004\001T\004\261\004\304\005\004\243\001T\237\004\304\005\310\005\001T\004\310\005\311\005\004\243\001T\237", block_len=1) at /home/simark/src/binutils-gdb/gdb/dwarf2/loc.c:1365
>>> #9 0x000055555e094d40 in loclist_read_variable_at_entry (symbol=0x621007a99bd0, frame=0x621007acc510) at /home/simark/src/binutils-gdb/gdb/dwarf2/loc.c:3889
>>> #10 0x000055555f5192e0 in read_frame_arg (fp_opts=..., sym=0x621007a99bd0, frame=0x621007acc510, argp=0x7fffffffbf20, entryargp=0x7fffffffbf60) at /home/simark/src/binutils-gdb/gdb/stack.c:559
>>> #11 0x000055555f51c352 in print_frame_args (fp_opts=..., func=0x621007a99ad0, frame=0x621007acc510, num=-1, stream=0x6030000bad90) at /home/simark/src/binutils-gdb/gdb/stack.c:887
>>> #12 0x000055555f521919 in print_frame (fp_opts=..., frame=0x621007acc510, print_level=1, print_what=LOCATION, print_args=1, sal=...) at /home/simark/src/binutils-gdb/gdb/stack.c:1390
>>> #13 0x000055555f51f22e in print_frame_info (fp_opts=..., frame=0x621007acc510, print_level=1, print_what=LOCATION, print_args=1, set_current_sal=0) at /home/simark/src/binutils-gdb/gdb/stack.c:1116
>>> #14 0x000055555f526c6d in backtrace_command_1 (fp_opts=..., bt_opts=..., count_exp=0x0, from_tty=0) at /home/simark/src/binutils-gdb/gdb/stack.c:2079
>>> #15 0x000055555f527ae5 in backtrace_command (arg=0x0, from_tty=0) at /home/simark/src/binutils-gdb/gdb/stack.c:2198
>>>
>>> The problem is that the type that gets passed down to
>>> dwarf_expr_context::fetch_result (the type of a variable of which we're
>>> trying to read the entry value) is a typedef whose size has never been
>>> computed yet (check_typedef has never been called on it). As we get in
>>> the DWARF_VALUE_STACK case (line 1028 of dwarf2/expr.c), the `len`
>>> variable is therefore set to 0, instead of the actual type length. We
>>> then call allocate_value on subobj_type, which does call check_typedef,
>>> so the length of the typedef gets filled in at that point. We end up
>>> passing to the copy function a source array view of length 0 and a
>>> target array view of length 4, and the assertion fails.
>>>
>>> Fix this by calling check_typedef on both type and subobj_type at the
>>> beginning of fetch_result.
>>>
>>> I tried writing a test for this using the DWARF assembler, but I haven't
>>> succeeded. It's possible that we need to get into this specific code
>>> path (value_of_dwarf_reg_entry and all) to manage to get to
>>> dwarf_expr_context::fetch_result with a typedef type that has never been
>>> resolved. In all my attempts, the typedef would always be resolved
>>> already, so the bug wouldn't show up.
>>>
>>> As a fallback, I made a gdb.dwarf2 test with compiler-generated .S
>>> files. I don't particularly like those, but I think it's better than no
>>> test. The .cpp source code is the smallest reproducer I am able to make
>>> from the reproducer given in the bug (thanks to Pedro for suggestions on
>>> how to minimize it further than I had). Since I tested on both amd64
>>> and aarch64, I added versions of the test for these two architectures.
>>>
>>> Change-Id: I182733ad08e34df40d8bcc47af72c482fabf4900
>>> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29374
>>> ---
>>> gdb/dwarf2/expr.c | 5 +
>>> .../gdb.dwarf2/entry-value-typedef-aarch64.S | 12885 +++++++++++++
>>> .../gdb.dwarf2/entry-value-typedef-amd64.S | 15545 ++++++++++++++++
>>> .../gdb.dwarf2/entry-value-typedef.cpp | 36 +
>>> .../gdb.dwarf2/entry-value-typedef.exp | 45 +
>>> 5 files changed, 28516 insertions(+)
>>> create mode 100644 gdb/testsuite/gdb.dwarf2/entry-value-typedef-aarch64.S
>>> create mode 100644 gdb/testsuite/gdb.dwarf2/entry-value-typedef-amd64.S
>>> create mode 100644 gdb/testsuite/gdb.dwarf2/entry-value-typedef.cpp
>>> create mode 100644 gdb/testsuite/gdb.dwarf2/entry-value-typedef.exp
>>
>> I pushed this patch.
>>
>> Simon
>
> It seems newer compilers on aarch64 (g++ 9.4.0 or 11.2.0) don't like this test. They complain with:
>
> gdb compile failed, /usr/bin/ld: /tmp/cc0vjoZT.o: relocation R_AARCH64_ADR_PREL_PG_HI21 against symbol `_ZNSsD1Ev@@GLIBCXX_3.4' which may bin
> d externally can not be used when making a shared object; recompile with -fPIC
> /usr/bin/ld: /tmp/cc0vjoZT.o(.text+0x38): unresolvable R_AARCH64_ADR_PREL_PG_HI21 relocation against symbol `_ZNSsD1Ev@@GLIBCXX_3.4'
> /usr/bin/ld: final link failed: bad value
>
> So the test doesn't run properly.
Is is that the old compiler I used (g++ 4.8 on Ubuntu 14.04, on the
compile farm) generated non-position-independent code, but the linker
of the newer toolchains try to build a position-independent executable?
If so, we can re-generate the assembly files with -fPIE, and it should
work, right? I'll give this a try, I have access to an AArch64 machine
with Debian 11 & g++ 10.2.1.
Simon
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