From: "H.J. Lu" <hjl.tools@gmail.com>
To: gnu-gabi@sourceware.org
Subject: Specify how undefined weak symbol should be resolved in executable
Date: Fri, 01 Jan 2016 00:00:00 -0000 [thread overview]
Message-ID: <CAMe9rOqQ-RUhBo3NATttc1VEGhtx4D0Z9aRWfw5APfDVuBPqWQ@mail.gmail.com> (raw)
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.
I raised the issue at gABI:
https://groups.google.com/d/msg/generic-abi/Ckq19PfLxyk/eCbXPofkAQAJ
But if gABI change is incompatible with other OSes, we need to
specify it in GNU ABI.
--
H.J.
next reply other threads:[~2016-02-22 16:25 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-01 0:00 H.J. Lu [this message]
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Michael Matz
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Michael Matz
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Alan Modra
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Michael Matz
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Michael Matz
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Alan Modra
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Alan Modra
2016-01-01 0:00 ` Carlos O'Donell
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Michael Matz
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Michael Matz
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Michael Matz
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Michael Matz
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` Michael Matz
2016-01-01 0:00 ` Szabolcs Nagy
2016-01-01 0:00 ` Michael Matz
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` H.J. Lu
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