https://sourceware.org/bugzilla/show_bug.cgi?id=26163
Bug ID: 26163
Summary: Combination of LTO and -Wl,--defsym causes symbol to
be resolved as NULL
Product: binutils
Version: 2.34
Status: NEW
Severity: normal
Priority: P2
Component: ld
Assignee: unassigned at sourceware dot org
Reporter: cbaylis at gcc dot gnu.org
Target Milestone: ---
Originally reported to GCC bugzilla
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95846
The following program demonstrates this problem:
==============< test1.c >==================
#include <stdio.h>
void f(void);
void g(void);
void f(void)
{
printf("in f()\n");
g();
printf("back in f()\n");
}
==============< test2.c >==================
#include <stdio.h>
void f(void);
void real_g(void)
{
printf("in real_g()\n");
}
int main()
{
real_g();
f();
}
============== end ==================
$ gcc -Os -c test1.c
$ gcc -O2 -flto -c test2.c
$ gcc -O2 test1.o test2.o -o test -Wl,--defsym,g=real_g
$ ./test
in real_g()
in f()
Segmentation fault (core dumped)
The segfault is caused because there is no real_g symbol and g has been
resolved to NULL.
0000000000401146 <f>:
401146: 50 push %rax
401147: bf 15 20 40 00 mov $0x402015,%edi
40114c: e8 df fe ff ff callq 401030 <puts@plt>
401151: e8 aa ee bf ff callq 0 <g> <---------------- oops!
401156: bf 10 20 40 00 mov $0x402010,%edi
40115b: 5a pop %rdx
40115c: e9 cf fe ff ff jmpq 401030 <puts@plt>
401161: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1)
401168: 00 00 00
40116b: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
Seen on Fedora 32 (gcc 10.1.1, binutils 2.34) and Ubuntu 18.04 (gcc 7.5.0,
binutils 2.30)
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