https://sourceware.org/bugzilla/show_bug.cgi?id=19704
Bug ID: 19704
Summary: Missing dynamic relocation against undefined weak
symbol
Product: binutils
Version: 2.27 (HEAD)
Status: NEW
Severity: normal
Priority: P2
Component: ld
Assignee: unassigned at sourceware dot org
Reporter: hjl.tools at gmail dot com
Target Milestone: ---
Currently when building executable, undefined weak symbol is resolved
differently, depending on if the relocatable input is compiled with PIC or
not:
hjl@gnu-tools-1 weak-1]$ cat x.c
extern void __attribute__ ((weak)) fun (void);
int main (void)
{
if (&fun != 0)
fun ();
return 0;
}
[hjl@gnu-tools-1 weak-1]$ make
gcc -B./ -O2 -o x x.c
gcc -B./ -O2 -o y x.c -fPIC
readelf -r x
Relocation section '.rela.dyn' at offset 0x328 contains 1 entries:
Offset Info Type Sym. Value Sym. Name +
Addend
000000600870 000200000006 R_X86_64_GLOB_DAT 0000000000000000 __gmon_start__ +
0
Relocation section '.rela.plt' at offset 0x340 contains 1 entries:
Offset Info Type Sym. Value Sym. Name +
Addend
000000600890 000100000007 R_X86_64_JUMP_SLO 0000000000000000
__libc_start_main@GLIBC_2.2.5 + 0
There is no dynamic relocation against fun, whose value is
resolved to zero at link-time.
readelf -r y
Relocation section '.rela.dyn' at offset 0x348 contains 2 entries:
Offset Info Type Sym. Value Sym. Name +
Addend
0000006008a0 000100000006 R_X86_64_GLOB_DAT 0000000000000000 fun + 0
0000006008a8 000300000006 R_X86_64_GLOB_DAT 0000000000000000 __gmon_start__ +
0
Relocation section '.rela.plt' at offset 0x378 contains 1 entries:
Offset Info Type Sym. Value Sym. Name +
Addend
0000006008c8 000200000007 R_X86_64_JUMP_SLO 0000000000000000
__libc_start_main@GLIBC_2.2.5 + 0
[hjl@gnu-tools-1 weak-1]$
There is dynamic relocation against fun, whose value is resolved
at runt-time. We should make it consistent, regardless if input
relocatable file is compiled with PIC or not. GNU ABI should be
extended to:
When creating executable, if dynamic relocation is available at
run-time, the link editor should generate dynamic relocations
against unresolved weak symbols so that their values will be
resolved at run-time.
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