53e8a631a0
https://sourceware.org/ml/gdb-patches/2014-05/msg00737.html Currently a MEMORY_ERROR raised during unwinding a frame will cause the unwind to stop with an error message, for example: (gdb) bt #0 breakpt () at amd64-invalid-stack-middle.c:27 #1 0x00000000004008f0 in func5 () at amd64-invalid-stack-middle.c:32 #2 0x0000000000400900 in func4 () at amd64-invalid-stack-middle.c:38 #3 0x0000000000400910 in func3 () at amd64-invalid-stack-middle.c:44 #4 0x0000000000400928 in func2 () at amd64-invalid-stack-middle.c:50 Cannot access memory at address 0x2aaaaaab0000 However, frame #4 is marked as being the end of the stack unwind, so a subsequent request for the backtrace looses the error message, such as: (gdb) bt #0 breakpt () at amd64-invalid-stack-middle.c:27 #1 0x00000000004008f0 in func5 () at amd64-invalid-stack-middle.c:32 #2 0x0000000000400900 in func4 () at amd64-invalid-stack-middle.c:38 #3 0x0000000000400910 in func3 () at amd64-invalid-stack-middle.c:44 #4 0x0000000000400928 in func2 () at amd64-invalid-stack-middle.c:50 When fetching the backtrace, or requesting the stack depth using the MI interface the situation is even worse, the first time a request is made we encounter the memory error and so the MI returns an error instead of the correct result, for example: (gdb) -stack-info-depth ^error,msg="Cannot access memory at address 0x2aaaaaab0000" Or, (gdb) -stack-list-frames ^error,msg="Cannot access memory at address 0x2aaaaaab0000" However, once one of these commands has been used gdb has, internally, walked the stack and figured that out that frame #4 is the bottom of the stack, so the second time an MI command is tried you'll get the "expected" result: (gdb) -stack-info-depth ^done,depth="5" Or, (gdb) -stack-list-frames ^done,stack=[frame={level="0", .. snip lots .. }] After this patch the MEMORY_ERROR encountered during the frame unwind is attached to frame #4 as the stop reason, and is displayed in the CLI each time the backtrace is requested. In the MI, catching the error means that the "expected" result is returned the first time the MI command is issued. So, from the CLI the results of the backtrace will be: (gdb) bt #0 breakpt () at amd64-invalid-stack-middle.c:27 #1 0x00000000004008f0 in func5 () at amd64-invalid-stack-middle.c:32 #2 0x0000000000400900 in func4 () at amd64-invalid-stack-middle.c:38 #3 0x0000000000400910 in func3 () at amd64-invalid-stack-middle.c:44 #4 0x0000000000400928 in func2 () at amd64-invalid-stack-middle.c:50 Backtrace stopped: Cannot access memory at address 0x2aaaaaab0000 Each and every time that the backtrace is requested, while the MI output will similarly be consistently: (gdb) -stack-info-depth ^done,depth="5" Or, (gdb) -stack-list-frames ^done,stack=[frame={level="0", .. snip lots .. }] gdb/ChangeLog: * frame.c (struct frame_info): Add stop_string field. (get_prev_frame_always_1): Renamed from get_prev_frame_always. (get_prev_frame_always): Old content moved into get_prev_frame_always_1. Call get_prev_frame_always_1 inside TRY_CATCH, handle MEMORY_ERROR exceptions. (frame_stop_reason_string): New function definition. * frame.h (unwind_stop_reason_to_string): Extend comment to mention frame_stop_reason_string. (frame_stop_reason_string): New function declaration. * stack.c (frame_info): Switch to frame_stop_reason_string. (backtrace_command_1): Switch to frame_stop_reason_string. * unwind_stop_reason.def: Add UNWIND_MEMORY_ERROR. (LAST_ENTRY): Changed to UNWIND_MEMORY_ERROR. * guile/lib/gdb.scm: Add FRAME_UNWIND_MEMORY_ERROR to export list. gdb/doc/ChangeLog: * guile.texi (Frames In Guile): Mention FRAME_UNWIND_MEMORY_ERROR. * python.texi (Frames In Python): Mention gdb.FRAME_UNWIND_MEMORY_ERROR. gdb/testsuite/ChangeLog: * gdb.arch/amd64-invalid-stack-middle.exp: Update expected results. * gdb.arch/amd64-invalid-stack-top.exp: Likewise.
80 lines
3 KiB
Text
80 lines
3 KiB
Text
# Copyright (C) 2014 Free Software Foundation, Inc.
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#
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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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#
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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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#
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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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# In this test we're looking at how gdb handles backtraces and
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# investigating the stack depth when confronted with an "invalid" stack,
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# that is a stack where the first few frames are normal, and then there's a
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# frame where the stack in unreadable.
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#
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# One interesting bug that has been observed is that gdb will sometime
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# exhibit different behaviour the first time a stack command is run
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# compared to the second (and later) times a command is run. This is
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# because the first time a command is run gdb actually tries to figure out
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# the answer, while the second (and later) times gdb relies on the answer
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# cached from the first time. As a result in this test each command is
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# run twice, and we restart gdb before testing each different command to
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# ensure that nothing is being cached.
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set opts {}
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standard_testfile .c
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if { ![istarget x86_64-*-* ] || ![is_lp64_target] } {
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verbose "Skipping ${testfile}."
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return
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}
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if { [prepare_for_testing ${testfile}.exp ${testfile} ${srcfile} $opts] } {
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return -1
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}
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if ![runto breakpt] {
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return -1
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}
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# Use 'bt no-filters' here as the python filters will raise their own
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# error during initialisation, the no-filters case is simpler.
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gdb_test "bt no-filters" "^bt no-filters\r\n#0 +$hex in func2 \\(\\)\r\nBacktrace stopped: Cannot access memory at address 0x\[0-9a-f\]+" \
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"first backtrace, with error message"
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gdb_test "bt no-filters" "^bt no-filters\r\n#0 +$hex in func2 \\(\\)\r\nBacktrace stopped: Cannot access memory at address 0x\[0-9a-f\]+" \
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"second backtrace, with error message"
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clean_restart ${binfile}
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if ![runto breakpt] {
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return -1
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}
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gdb_test "interpreter-exec mi \"-stack-info-depth\"" \
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"\\^done,depth=\"1\"" \
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"check mi -stack-info-depth command, first time"
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gdb_test "interpreter-exec mi \"-stack-info-depth\"" \
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"\\^done,depth=\"1\"" \
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"check mi -stack-info-depth command, second time"
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clean_restart ${binfile}
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if ![runto breakpt] {
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return -1
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}
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gdb_test "interpreter-exec mi \"-stack-list-frames\"" \
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"\\^done,stack=\\\[frame=\{level=\"0\",addr=\"$hex\",func=\"func2\"\}\\\]" \
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"check mi -stack-list-frames command, first time"
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gdb_test "interpreter-exec mi \"-stack-list-frames\"" \
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"\\^done,stack=\\\[frame=\{level=\"0\",addr=\"$hex\",func=\"func2\"\}\\\]" \
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"check mi -stack-list-frames command, second time"
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