i386: Use "movl main@GOT(%ebx), %eax" in start.S
Commit Message
Don't use "leal main@GOTOFF(%ebx), %eax" since main may be in a
shared object. Linker will convert "movl main@GOT(%ebx), %eax"
to "leal main@GOTOFF(%ebx), %eax" if main is defined locally.
Any comments?
H.J.
---
* sysdeps/i386/start.S: Replace "leal main@GOT(%ebx), %eax" with
"movl main@GOTOFF(%ebx), %eax".
---
sysdeps/i386/start.S | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
Comments
* H. J. Lu:
> Don't use "leal main@GOTOFF(%ebx), %eax" since main may be in a
> shared object. Linker will convert "movl main@GOT(%ebx), %eax"
> to "leal main@GOTOFF(%ebx), %eax" if main is defined locally.
>
> Any comments?
Would it be worthwhile to add a test for this which is not
architecture-specific?
On 10/3/17, Florian Weimer <fw@deneb.enyo.de> wrote:
> * H. J. Lu:
>
>> Don't use "leal main@GOTOFF(%ebx), %eax" since main may be in a
>> shared object. Linker will convert "movl main@GOT(%ebx), %eax"
>> to "leal main@GOTOFF(%ebx), %eax" if main is defined locally.
>>
>> Any comments?
>
> Would it be worthwhile to add a test for this which is not
> architecture-specific?
>
Yes, a patch is here:
https://sourceware.org/ml/libc-alpha/2017-10/msg00104.html
On 10/3/17, H.J. Lu <hjl.tools@gmail.com> wrote:
> On 10/3/17, Florian Weimer <fw@deneb.enyo.de> wrote:
>> * H. J. Lu:
>>
>>> Don't use "leal main@GOTOFF(%ebx), %eax" since main may be in a
>>> shared object. Linker will convert "movl main@GOT(%ebx), %eax"
>>> to "leal main@GOTOFF(%ebx), %eax" if main is defined locally.
>>>
>>> Any comments?
>>
>> Would it be worthwhile to add a test for this which is not
>> architecture-specific?
>>
>
> Yes, a patch is here:
>
> https://sourceware.org/ml/libc-alpha/2017-10/msg00104.html
>
>
I am checking it in.
@@ -99,8 +99,11 @@ _start:
pushl main@GOT(%ebx)
# else
/* Avoid relocation in static PIE since _start is called before
- it is relocated. */
- leal main@GOTOFF(%ebx), %eax
+ it is relocated. Don't use "leal main@GOTOFF(%ebx), %eax"
+ since main may be in a shared object. Linker will convert
+ "movl main@GOT(%ebx), %eax" to "leal main@GOTOFF(%ebx), %eax"
+ if main is defined locally. */
+ movl main@GOT(%ebx), %eax
pushl %eax
# endif