On aarch64-linux, I run into: ... (gdb) PASS: gdb.python/py-disasm.exp: global_disassembler=ReadMemoryGdbErrorDisassembler: python add_global_disassembler(ReadMemoryGdbErrorDisassembler) disassemble test^M Dump of assembler code for function test:^M 0x00000000004005e4 <+0>: nop^M terminate called after throwing an instance of 'gdbpy_err_fetch'^M ^M ^M Fatal signal: Aborted^M ----- Backtrace -----^M 0x55dc4f gdb_internal_backtrace_1^M /home/tdevries/gdb/src/gdb/bt-utils.c:122^M 0x55dd0f _Z22gdb_internal_backtracev^M /home/tdevries/gdb/src/gdb/bt-utils.c:168^M 0x739383 handle_fatal_signal^M /home/tdevries/gdb/src/gdb/event-top.c:964^M 0xffffbe4eb7cb ???^M 0xffffbda48500 ???^M 0xffffbda498a3 ???^M 0xffffbdc74173 ???^M 0xffffbdc71c9b ???^M 0xffffbdc71cff ???^M 0xffffbdc71fe3 ???^M 0x8f1f0f _ZN18gdbpy_disassembler16read_memory_funcEmPhjP16disassemble_info^M /home/tdevries/gdb/src/gdb/python/py-disasm.c:516^M 0xbd8753 print_insn_aarch64^M /home/tdevries/gdb/src/opcodes/aarch64-dis.c:3982^M ---------------------^M A fatal error internal to GDB has been detected, further^M debugging is not possible. GDB will now terminate.^M ^M This is a bug, please report it. For instructions, see:^M <https://www.gnu.org/software/gdb/bugs/>.^M ^M ERROR: GDB process no longer exists GDB process exited with wait status 20369 exp48 0 0 CHILDKILLED SIGABRT SIGABRT UNRESOLVED: gdb.python/py-disasm.exp: global_disassembler=ReadMemoryGdbErrorDisassembler: disassemble test ...
I tried to reproduce this using: ... $ ./build/gdb/gdb -q -batch -ex "set trace-commands on" -x outputs/gdb.python/py-disasm/gdb.in.1 ... but didn't manage because some disasm commands fail, so I tried to prefix all disasm commands using ignore-errors ( https://sourceware.org/pipermail/gdb-patches/2021-May/178990.html ), but found that that still stopped script execution. I was able to repair this by doing: ... diff --git a/gdb/disasm.c b/gdb/disasm.c index de44aac3263..b1ba119db9e 100644 --- a/gdb/disasm.c +++ b/gdb/disasm.c @@ -454,7 +454,7 @@ gdb_pretty_print_disassembler::pretty_print_insn (const struct disasm_insn *insn object destructor as the write itself might throw an exception if the pager kicks in, and the user selects quit. */ write_out_insn_buffer (); - throw ex; + throw; } if ((flags & (DISASSEMBLY_RAW_INSN | DISASSEMBLY_RAW_BYTES)) != 0) ... It's possible that the ignore-errors code should try harder to catch errors, but this change doesn't look wrong.
Minimal gdb.in to reproduce: ... file /home/tdevries/gdb/build/gdb/testsuite/outputs/gdb.python/py-disasm/py-disasm start source /home/tdevries/gdb/build/gdb/testsuite/outputs/gdb.python/py-disasm/py-disasm.py break 22 continue print/x $pc python current_pc = 0x4005e8 python remove_all_python_disassemblers() python add_global_disassembler(ReadMemoryGdbErrorDisassembler) disassemble test ...
Well, this is weird. I apply this patch: ... diff --git a/gdb/python/py-disasm.c b/gdb/python/py-disasm.c index c37452fcf72..8d684a98eb9 100644 --- a/gdb/python/py-disasm.c +++ b/gdb/python/py-disasm.c @@ -294,12 +294,12 @@ disasmpy_builtin_disassemble (PyObject *self, PyObject *args, PyObject *kw) length = gdbarch_print_insn (disasm_info->gdbarch, disasm_info->address, disassembler.disasm_info ()); } - catch (gdbpy_err_fetch &pyerr) + catch (...) { /* Reinstall the Python exception held in PYERR. This clears to pointers held in PYERR, hence the need to catch as a non-const reference. */ - pyerr.restore (); + //pyerr.restore (); return nullptr; } ... and do a catch throw, and a bt to see the callstack at the point of the throw: ... (gdb) bt #0 0x0000fffff7782f9c in __cxa_throw () from /usr/lib64/libstdc++.so.6 #1 0x00000000008f1e1c in gdbpy_disassembler::read_memory_func (memaddr=4195816, buff=0xffffffffd1d8 "\370\353d", len=4, info=0xffffffffd350) at /home/tdevries/gdb/src/gdb/python/py-disasm.c:516 #2 0x0000000000bd8660 in print_insn_aarch64 (pc=4195816, info=0xffffffffd350) at /home/tdevries/gdb/src/opcodes/aarch64-dis.c:3982 #3 0x00000000004a8ad8 in default_print_insn (memaddr=4195816, info=0xffffffffd350) at /home/tdevries/gdb/src/gdb/arch-utils.c:1033 #4 0x0000000000429b5c in aarch64_gdb_print_insn (memaddr=4195816, info=0xffffffffd350) at /home/tdevries/gdb/src/gdb/aarch64-tdep.c:2235 #5 0x00000000004b36a8 in gdbarch_print_insn (gdbarch=0x165d810, vma=4195816, info=0xffffffffd350) at /home/tdevries/gdb/src/gdb/gdbarch.c:3351 #6 0x00000000008f163c in disasmpy_builtin_disassemble ( self=<module at remote 0xfffff40678b8>, args=(<MyInfo at remote 0xffffdec57048>,), kw=0x0) at /home/tdevries/gdb/src/gdb/python/py-disasm.c:294 ... It looks clear that the exception thrown should be caught by the catch clause in disasmpy_builtin_disassemble, but it doesn't. Maybe -fexceptions missing on the opcodes file or some such.
(In reply to Tom de Vries from comment #3) > Maybe -fexceptions missing on the opcodes file or some such. Yep, this patch is sufficient to make the test-case pass on aarch64: ... diff --git a/opcodes/Makefile.in b/opcodes/Makefile.in index fe4539d6097..03efe198461 100644 --- a/opcodes/Makefile.in +++ b/opcodes/Makefile.in @@ -206,11 +206,11 @@ depcomp = $(SHELL) $(top_srcdir)/../depcomp am__depfiles_maybe = depfiles am__mv = mv -f COMPILE = $(CC) $(DEFS) $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) \ - $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS) + $(CPPFLAGS) $(AM_CFLAGS) $(CFLAGS) -fexceptions LTCOMPILE = $(LIBTOOL) $(AM_V_lt) --tag=CC $(AM_LIBTOOLFLAGS) \ $(LIBTOOLFLAGS) --mode=compile $(CC) $(DEFS) \ $(DEFAULT_INCLUDES) $(INCLUDES) $(AM_CPPFLAGS) $(CPPFLAGS) \ - $(AM_CFLAGS) $(CFLAGS) + $(AM_CFLAGS) $(CFLAGS) -fexceptions AM_V_CC = $(am__v_CC_@AM_V@) am__v_CC_ = $(am__v_CC_@AM_DEFAULT_V@) am__v_CC_0 = @echo " CC " $@; ...
Created attachment 14411 [details] Possible patch for this problem Here's my proposal for fixing this issue. This patch avoids the throw/catch over libopcode. I've tested this on aarch64 and it seems to fix the issue. I'm still running the full testsuite.
(In reply to Andrew Burgess from comment #5) > Created attachment 14411 [details] > Possible patch for this problem > > Here's my proposal for fixing this issue. This patch avoids the throw/catch > over libopcode. I've tested this on aarch64 and it seems to fix the issue. > I'm still running the full testsuite. Thanks. I'll submit the patch from comment 1.
(In reply to Tom de Vries from comment #6) > (In reply to Andrew Burgess from comment #5) > > Created attachment 14411 [details] > > Possible patch for this problem > > > > Here's my proposal for fixing this issue. This patch avoids the throw/catch > > over libopcode. I've tested this on aarch64 and it seems to fix the issue. > > I'm still running the full testsuite. > > Thanks. > > I'll submit the patch from comment 1. https://sourceware.org/pipermail/gdb-patches/2022-October/193067.html
And I posted my part here: https://sourceware.org/pipermail/gdb-patches/2022-October/193079.html
Andrew requested that this be included in the GDB 13 release, and it seems like a good idea, so marking the Target Milestone to 13.1.
Thanks for addressing this.
The master branch has been updated by Andrew Burgess <aburgess@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=65639fcc54226c0621d4312efac702c92ddde324 commit 65639fcc54226c0621d4312efac702c92ddde324 Author: Andrew Burgess <aburgess@redhat.com> Date: Fri Oct 21 16:20:58 2022 +0100 gdb/python: avoid throwing an exception over libopcodes code Bug gdb/29712 identifies a problem with the Python disassembler API. In some cases GDB will try to throw an exception through the libopcodes disassembler code, however, not all targets include exception unwind information when compiling C code, for targets that don't include this information GDB will terminate when trying to pass the exception through libopcodes. To explain what GDB is trying to do, consider the following trivial use of the Python disassembler API: class ExampleDisassembler(gdb.disassembler.Disassembler): class MyInfo(gdb.disassembler.DisassembleInfo): def __init__(self, info): super().__init__(info) def read_memory(self, length, offset): return super().read_memory(length, offset) def __init__(self): super().__init__("ExampleDisassembler") def __call__(self, info): info = self.MyInfo(info) return gdb.disassembler.builtin_disassemble(info) This disassembler doesn't add any value, it defers back to GDB to do all the actual work, but it serves to allow us to discuss the problem. The problem occurs when a Python exception is raised by the MyInfo.read_memory method. The MyInfo.read_memory method is called from the C++ function gdbpy_disassembler::read_memory_func. The C++ stack at the point this function is called looks like this: #0 gdbpy_disassembler::read_memory_func (memaddr=4198805, buff=0x7fff9ab9d2a8 "\220Ó¹\232\377\177", len=1, info=0x7fff9ab9d558) at ../../src/gdb/python/py-disasm.c:510 #1 0x000000000104ba06 in fetch_data (info=0x7fff9ab9d558, addr=0x7fff9ab9d2a9 "Ó¹\232\377\177") at ../../src/opcodes/i386-dis.c:305 #2 0x000000000104badb in ckprefix (ins=0x7fff9ab9d100) at ../../src/opcodes/i386-dis.c:8571 #3 0x000000000104e28e in print_insn (pc=4198805, info=0x7fff9ab9d558, intel_syntax=-1) at ../../src/opcodes/i386-dis.c:9548 #4 0x000000000104f4d4 in print_insn_i386 (pc=4198805, info=0x7fff9ab9d558) at ../../src/opcodes/i386-dis.c:9949 #5 0x00000000004fa7ea in default_print_insn (memaddr=4198805, info=0x7fff9ab9d558) at ../../src/gdb/arch-utils.c:1033 #6 0x000000000094fe5e in i386_print_insn (pc=4198805, info=0x7fff9ab9d558) at ../../src/gdb/i386-tdep.c:4072 #7 0x0000000000503d49 in gdbarch_print_insn (gdbarch=0x5335560, vma=4198805, info=0x7fff9ab9d558) at ../../src/gdb/gdbarch.c:3351 #8 0x0000000000bcc8c6 in disasmpy_builtin_disassemble (self=0x7f2ab07f54d0, args=0x7f2ab0789790, kw=0x0) at ../../src/gdb/python/py-disasm.c:324 ### ... snip lots of frames as we pass through Python itself ... #22 0x0000000000bcd860 in gdbpy_print_insn (gdbarch=0x5335560, memaddr=0x401195, info=0x7fff9ab9e3c8) at ../../src/gdb/python/py-disasm.c:783 #23 0x00000000008995a5 in ext_lang_print_insn (gdbarch=0x5335560, address=0x401195, info=0x7fff9ab9e3c8) at ../../src/gdb/extension.c:939 #24 0x0000000000741aaa in gdb_print_insn_1 (gdbarch=0x5335560, vma=0x401195, info=0x7fff9ab9e3c8) at ../../src/gdb/disasm.c:1078 #25 0x0000000000741bab in gdb_disassembler::print_insn (this=0x7fff9ab9e3c0, memaddr=0x401195, branch_delay_insns=0x0) at ../../src/gdb/disasm.c:1101 So gdbpy_disassembler::read_memory_func is called from the libopcodes disassembler to read memory, this C++ function then calls into user supplied Python code to do the work. If the user supplied Python code raises an gdb.MemoryError exception indicating the memory read failed, this is fine. The C++ code converts this exception back into a return value that libopcodes can understand, and returns to libopcodes. However, if the user supplied Python code raises some other exception, what we want is for this exception to propagate through GDB and appear as if raised by the call to gdb.disassembler.builtin_disassemble. To achieve this, when gdbpy_disassembler::read_memory_func spots an unknown Python exception, we must pass the information about this exception from frame #0 to frame #8 in the above backtrace. Frame #8 is the C++ implementation of gdb.disassembler.builtin_disassemble, and so it is this function that we want to re-raise the unknown Python exception, so the user can, if they want, catch the exception in their code. The previous mechanism by which the exception was passed was to pack the details of the Python exception into a C++ exception, then throw the exception from frame #0, and catch the exception in frame #8, unpack the details of the Python exception, and re-raise it. However, this relies on the exception passing through frames #1 to #7, some of which are in libopcodes, which is C code, and so, might not be compiled with exception support. This commit proposes an alternative solution that does not rely on throwing a C++ exception. When we spot an unhandled Python exception in frame #0, we will store the details of this exception within the gdbpy_disassembler object currently in use. Then we return to libopcodes a value indicating that the memory_read failed. libopcodes will now continue to disassemble as though that memory read failed (with one special case described below), then, when we eventually return to disasmpy_builtin_disassemble we check to see if there is an exception stored in the gdbpy_disassembler object. If there is then this exception can immediately be installed, and then we return back to Python, when the user will be able to catch the exception. There is one extra change in gdbpy_disassembler::read_memory_func. After the first call that results in an exception being stored on the gdbpy_disassembler object, any future calls to the ::read_memory_func function will immediately return as if the read failed. This avoids any additional calls into user supplied Python code. My thinking here is that should the first call fail with some unknown error, GDB should not keep trying with any additional calls. This maintains the illusion that the exception raised from MyInfo.read_memory is immediately raised by gdb.disassembler.builtin_disassemble. I have no tests for this change though - to trigger this issue would rely on a libopcodes disassembler that will try to read further memory even after the first failed read. I'm not aware of any such disassembler that currently does this, but that doesn't mean such a disassembler couldn't exist in the future. With this change in place the gdb.python/py-disasm.exp test should now pass on AArch64. Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29712 Approved-By: Simon Marchi <simon.marchi@efficios.com>
The master branch has been updated by Andrew Burgess <aburgess@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=8eb7d135e32ad6b7cdcfeffe486b195058206cdb commit 8eb7d135e32ad6b7cdcfeffe486b195058206cdb Author: Andrew Burgess <aburgess@redhat.com> Date: Mon Oct 24 18:35:41 2022 +0100 gdb/disasm: mark functions passed to the disassembler noexcept While working on another patch, Simon pointed out that GDB could be improved by marking the functions passed to the disassembler as noexcept. https://sourceware.org/pipermail/gdb-patches/2022-October/193084.html The reason this is important is the on some hosts, libopcodes, being C code, will not be compiled with support for handling exceptions. As such, an attempt to throw an exception over libopcodes code will cause GDB to terminate. See bug gdb/29712 for an example of when this happened. In this commit all the functions that are passed to the disassembler, and which might be used as callbacks by libopcodes are marked noexcept. Ideally, I would have liked to change these typedefs: using read_memory_ftype = decltype (disassemble_info::read_memory_func); using memory_error_ftype = decltype (disassemble_info::memory_error_func); using print_address_ftype = decltype (disassemble_info::print_address_func); using fprintf_ftype = decltype (disassemble_info::fprintf_func); using fprintf_styled_ftype = decltype (disassemble_info::fprintf_styled_func); which are declared in disasm.h, as including the noexcept keyword. However, when I tried this, I ran into this warning/error: In file included from ../../src/gdb/disasm.c:25: ../../src/gdb/disasm.h: In constructor âgdb_printing_disassembler::gdb_printing_disassembler(gdbarch*, ui_file*, gdb_disassemble_info::read_memory_ftype, gdb_disassemble_info::memory_error_ftype, gdb_disassemble_info::print_address_ftype)â: ../../src/gdb/disasm.h:116:3: error: mangled name for âgdb_printing_disassembler::gdb_printing_disassembler(gdbarch*, ui_file*, gdb_disassemble_info::read_memory_ftype, gdb_disassemble_info::memory_error_ftype, gdb_disassemble_info::print_address_ftype)â will change in C++17 because the exception specification is part of a function type [-Werror=noexcept-type] 116 | gdb_printing_disassembler (struct gdbarch *gdbarch, | ^~~~~~~~~~~~~~~~~~~~~~~~~ So I've left that change out. This does mean that if somebody adds a new use of the disassembler classes in the future, and forgets to mark the callbacks as noexcept, this will compile fine. We'll just have to manually check for that during review.
Is this fixed now?
Thanks Tom. Yes this is fixed, I just forgot to close the bug.