6aa4f97c2b
This commit adds a new maintenance feature, the ability to print a (limited) backtrace if GDB dies due to a fatal signal. The backtrace is produced using the backtrace and backtrace_symbols_fd functions which are declared in the execinfo.h header, and both of which are async signal safe. A configure check has been added to check for these features, if they are not available then the new code is not compiled into GDB and the backtrace will not be printed. The motivation for this new feature is to aid in debugging GDB in situations where GDB has crashed at a users site, but the user is reluctant to share core files, possibly due to concerns about what might be in the memory image within the core file. Such a user might be happy to share a simple backtrace that was written to stderr. The production of the backtrace is on by default, but can switched off using the new commands: maintenance set backtrace-on-fatal-signal on|off maintenance show backtrace-on-fatal-signal Right now, I have hooked this feature in to GDB's existing handling of SIGSEGV only, but this will be extended to more signals in a later commit. One additional change I have made in this commit is that, when we decide GDB should terminate due to the fatal signal, we now raise the same fatal signal rather than raising SIGABRT. Currently, this is only effecting our handling of SIGSEGV. So, previously, if GDB hit a SEGV then we would terminate GDB with a SIGABRT. After this commit we will terminate GDB with a SIGSEGV. This feels like an improvement to me, we should still get a core dump, but in many shells, the user will see a more specific message once GDB exits, in bash for example "Segmentation fault" rather than "Aborted". Finally then, here is an example of the output a user would see if GDB should hit an internal SIGSEGV: Fatal signal: Segmentation fault ----- Backtrace ----- ./gdb/gdb[0x8078e6] ./gdb/gdb[0x807b20] /lib64/libpthread.so.0(+0x14b20)[0x7f6648c92b20] /lib64/libc.so.6(__poll+0x4f)[0x7f66484d3a5f] ./gdb/gdb[0x1540f4c] ./gdb/gdb[0x154034a] ./gdb/gdb[0x9b002d] ./gdb/gdb[0x9b014d] ./gdb/gdb[0x9b1aa6] ./gdb/gdb[0x9b1b0c] ./gdb/gdb[0x41756d] /lib64/libc.so.6(__libc_start_main+0xf3)[0x7f66484041a3] ./gdb/gdb[0x41746e] --------------------- A fatal error internal to GDB has been detected, further debugging is not possible. GDB will now terminate. This is a bug, please report it. For instructions, see: <https://www.gnu.org/software/gdb/bugs/>. Segmentation fault (core dumped) It is disappointing that backtrace_symbols_fd does not actually map the addresses back to symbols, this appears, in part, to be due to GDB not being built with -rdynamic as the manual page for backtrace_symbols_fd suggests, however, even when I do add -rdynamic to the build of GDB I only see symbols for some addresses. We could potentially look at alternative libraries to provide the backtrace (e.g. libunwind) however, the solution presented here, which is available as part of glibc is probably a good baseline from which we might improve things in future.
22 lines
759 B
C
22 lines
759 B
C
/* Copyright 2021 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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int
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main (void)
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{
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return 0;
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}
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