From: "H.J. Lu" <hjl.tools@gmail.com>
To: gnu-gabi@sourceware.org
Subject: Re: Specify how undefined weak symbol should be resolved in executable
Date: Fri, 01 Jan 2016 00:00:00 -0000 [thread overview]
Message-ID: <CAMe9rOri=tgoHD3RU5L0hgeh4vxWMmgZ8Wf1QOFgZjcJ7tqDpg@mail.gmail.com> (raw)
In-Reply-To: <CAMe9rOoJkeBS1_=DaEUY8Ts+=b7A=83_0wgVfCa3g+dd3me4wg@mail.gmail.com>
On Mon, Feb 22, 2016 at 9:45 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Mon, Feb 22, 2016 at 8:25 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> 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.
>
> We should extend GNU ABI 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.
>
I opened:
https://sourceware.org/bugzilla/show_bug.cgi?id=19704
--
H.J.
next prev parent reply other threads:[~2016-02-22 17:50 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-01 0:00 H.J. Lu
2016-01-01 0:00 ` H.J. Lu
2016-01-01 0:00 ` H.J. Lu [this message]
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 ` 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
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