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545e49f5ee
Consider test-case test.c:
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int main (void) {
void *p = malloc (10);
return 0;
}
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When compiled to a non-PIE exec:
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$ gcc -m32 test.c
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the call sequence looks like:
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8048447: 83 ec 0c sub $0xc,%esp
804844a: 6a 0a push $0xa
804844c: e8 bf fe ff ff call 8048310 <malloc@plt>
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which calls to:
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08048310 <malloc@plt>:
8048310: ff 25 0c a0 04 08 jmp *0x804a00c
8048316: 68 00 00 00 00 push $0x0
804831b: e9 e0 ff ff ff jmp 8048300 <.plt>
...
where the first insn at 0x8048310 initially jumps to the following address
0x8048316, read from the .got.plt @ 0x804a00c:
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804a000 0c9f0408 00000000 00000000 16830408 ................
804a010 26830408 &...
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Likewise, when compiled as a PIE:
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$ gcc -m32 -fPIE -pie test.c
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we have this call sequence (with %ebx setup to point to the .got.plt):
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0000055d <main>:
579: 83 ec 0c sub $0xc,%esp
57c: 6a 0a push $0xa
57e: 89 c3 mov %eax,%ebx
580: e8 6b fe ff ff call 3f0 <malloc@plt>
...
which calls to:
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000003f0 <malloc@plt>:
3f0: ff a3 0c 00 00 00 jmp *0xc(%ebx)
3f6: 68 00 00 00 00 push $0x0
3fb: e9 e0 ff ff ff jmp 3e0 <.plt>
...
where the insn at 0x3f0 initially jumps to following address 0x3f6, read from
the .got.plt at offset 0xc:
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2000 f41e0000 00000000 00000000 f6030000 ................
2010 06040000 ....
...
When instead doing an inferior call to malloc (with nosharedlib to force
malloc to resolve to malloc@plt rather than the functions in ld.so or libc.so)
with the non-PIE exec, we have the expected:
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$ gdb -q -batch a.out -ex start -ex nosharedlib -ex "p /x (void *)malloc (10)"
Temporary breakpoint 1 at 0x8048444
Temporary breakpoint 1, 0x08048444 in main ()
$1 = 0x804b160
...
But with the PIE exec, we run into:
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$ gdb -q -batch a.out -ex start -ex nosharedlib -ex "p /x (void *)malloc (10)"
Temporary breakpoint 1 at 0x56c
Temporary breakpoint 1, 0x5655556c in main ()
Program received signal SIGSEGV, Segmentation fault.
0x565553f0 in malloc@plt ()
...
The segfault happens because:
- the inferior call mechanism doesn't setup %ebx
- %ebx instead is 0
- the jump to "*0xc(%ebx)" reads from memory at 0xc
Fix this by setting up %ebx properly in i386_thiscall_push_dummy_call.
Fixes this failure with target board unix/-m32/-pie/-fPIE reported in
PR28467:
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FAIL: gdb.base/nodebug.exp: p/c (int) array_index("abcdef",2)
...
Tested on x86_64-linux, with target board unix/-m32 and unix/-m32/-fPIE/-pie.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28467
70 lines
2.2 KiB
C++
70 lines
2.2 KiB
C++
/* Support for GDB maintenance commands.
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Copyright (C) 2013-2021 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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#ifndef MAINT_H
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#define MAINT_H
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#include "gdbsupport/run-time-clock.h"
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#include <chrono>
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extern void set_per_command_time (int);
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extern void set_per_command_space (int);
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/* Records a run time and space usage to be used as a base for
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reporting elapsed time or change in space. */
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class scoped_command_stats
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{
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public:
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explicit scoped_command_stats (bool msg_type);
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~scoped_command_stats ();
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private:
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DISABLE_COPY_AND_ASSIGN (scoped_command_stats);
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/* Print the time, along with a string. */
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void print_time (const char *msg);
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/* Zero if the saved time is from the beginning of GDB execution.
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One if from the beginning of an individual command execution. */
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bool m_msg_type;
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/* Track whether the stat was enabled at the start of the command
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so that we can avoid printing anything if it gets turned on by
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the current command. */
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int m_time_enabled : 1;
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int m_space_enabled : 1;
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int m_symtab_enabled : 1;
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run_time_clock::time_point m_start_cpu_time;
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std::chrono::steady_clock::time_point m_start_wall_time;
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long m_start_space;
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/* Total number of symtabs (over all objfiles). */
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int m_start_nr_symtabs;
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/* A count of the compunits. */
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int m_start_nr_compunit_symtabs;
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/* Total number of blocks. */
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int m_start_nr_blocks;
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};
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extern obj_section *maint_obj_section_from_bfd_section (bfd *abfd,
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asection *asection,
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objfile *ofile);
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#endif /* MAINT_H */
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