i386: Avoid avoid rely on linker optimization to avoid relocation
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| Context |
Check |
Description |
| dj/TryBot-apply_patch |
success
|
Patch applied to master at the time it was sent
|
| dj/TryBot-32bit |
success
|
Build for i686
|
Commit Message
lld does not implement all the linker optimization to avoid the GOT
relocation as done by binutils (bfd/elf32-i386.c:elf_i386_convert_load_reloc).
The current 'movl main@GOT(%ebx), %eax' will then create a GOT
relocation when building with lld, which make static-pie status to
not being able to start the provided main function.
The change uses a __wrap_main local symbol, which in turn calls main
(similar as used by aarch64 and s390x).
Checked on i686-linux-gnu with binutils and lld.
---
sysdeps/i386/start.S | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
Comments
On Thu, Nov 17, 2022 at 4:43 AM Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>
> lld does not implement all the linker optimization to avoid the GOT
> relocation as done by binutils (bfd/elf32-i386.c:elf_i386_convert_load_reloc).
> The current 'movl main@GOT(%ebx), %eax' will then create a GOT
> relocation when building with lld, which make static-pie status to
> not being able to start the provided main function.
>
> The change uses a __wrap_main local symbol, which in turn calls main
> (similar as used by aarch64 and s390x).
>
> Checked on i686-linux-gnu with binutils and lld.
> ---
> sysdeps/i386/start.S | 13 +++++++++----
> 1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/sysdeps/i386/start.S b/sysdeps/i386/start.S
> index 4ec04bdfd7..d593c4de00 100644
> --- a/sysdeps/i386/start.S
> +++ b/sysdeps/i386/start.S
> @@ -98,11 +98,10 @@ ENTRY (_start)
> pushl main@GOT(%ebx)
> # else
> /* Avoid relocation in static PIE since _start is called before
> - 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"
> + it is relocated. This also avoid rely on linker optimization to
> + transform 'movl main@GOT(%ebx), %eax' to 'leal main@GOTOFF(%ebx)'
> if main is defined locally. */
> - movl main@GOT(%ebx), %eax
> + leal __wrap_main@GOTOFF(%ebx), %eax
> pushl %eax
> # endif
>
> @@ -130,6 +129,12 @@ ENTRY (_start)
> 1: movl (%esp), %ebx
> ret
> #endif
> +
> +#if defined PIC && !defined SHARED
> +__wrap_main:
> + _CET_ENDBR
> + jmp main
Shouldn't it be "jmp main@PLT"?
> +#endif
> END (_start)
>
> /* To fulfill the System V/i386 ABI we need this symbol. Yuck, it's so
> --
> 2.34.1
>
On 17/11/22 13:07, H.J. Lu wrote:
> On Thu, Nov 17, 2022 at 4:43 AM Adhemerval Zanella
> <adhemerval.zanella@linaro.org> wrote:
>>
>> lld does not implement all the linker optimization to avoid the GOT
>> relocation as done by binutils (bfd/elf32-i386.c:elf_i386_convert_load_reloc).
>> The current 'movl main@GOT(%ebx), %eax' will then create a GOT
>> relocation when building with lld, which make static-pie status to
>> not being able to start the provided main function.
>>
>> The change uses a __wrap_main local symbol, which in turn calls main
>> (similar as used by aarch64 and s390x).
>>
>> Checked on i686-linux-gnu with binutils and lld.
>> ---
>> sysdeps/i386/start.S | 13 +++++++++----
>> 1 file changed, 9 insertions(+), 4 deletions(-)
>>
>> diff --git a/sysdeps/i386/start.S b/sysdeps/i386/start.S
>> index 4ec04bdfd7..d593c4de00 100644
>> --- a/sysdeps/i386/start.S
>> +++ b/sysdeps/i386/start.S
>> @@ -98,11 +98,10 @@ ENTRY (_start)
>> pushl main@GOT(%ebx)
>> # else
>> /* Avoid relocation in static PIE since _start is called before
>> - 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"
>> + it is relocated. This also avoid rely on linker optimization to
>> + transform 'movl main@GOT(%ebx), %eax' to 'leal main@GOTOFF(%ebx)'
>> if main is defined locally. */
>> - movl main@GOT(%ebx), %eax
>> + leal __wrap_main@GOTOFF(%ebx), %eax
>> pushl %eax
>> # endif
>>
>> @@ -130,6 +129,12 @@ ENTRY (_start)
>> 1: movl (%esp), %ebx
>> ret
>> #endif
>> +
>> +#if defined PIC && !defined SHARED
>> +__wrap_main:
>> + _CET_ENDBR
>> + jmp main
>
> Shouldn't it be "jmp main@PLT"?
My understanding is for static build we can handle main as hidden, so there
is no need use a PLT relocation here.
On Thu, Nov 17, 2022 at 8:42 AM Adhemerval Zanella Netto
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> On 17/11/22 13:07, H.J. Lu wrote:
> > On Thu, Nov 17, 2022 at 4:43 AM Adhemerval Zanella
> > <adhemerval.zanella@linaro.org> wrote:
> >>
> >> lld does not implement all the linker optimization to avoid the GOT
> >> relocation as done by binutils (bfd/elf32-i386.c:elf_i386_convert_load_reloc).
> >> The current 'movl main@GOT(%ebx), %eax' will then create a GOT
> >> relocation when building with lld, which make static-pie status to
> >> not being able to start the provided main function.
> >>
> >> The change uses a __wrap_main local symbol, which in turn calls main
> >> (similar as used by aarch64 and s390x).
> >>
> >> Checked on i686-linux-gnu with binutils and lld.
> >> ---
> >> sysdeps/i386/start.S | 13 +++++++++----
> >> 1 file changed, 9 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/sysdeps/i386/start.S b/sysdeps/i386/start.S
> >> index 4ec04bdfd7..d593c4de00 100644
> >> --- a/sysdeps/i386/start.S
> >> +++ b/sysdeps/i386/start.S
> >> @@ -98,11 +98,10 @@ ENTRY (_start)
> >> pushl main@GOT(%ebx)
> >> # else
> >> /* Avoid relocation in static PIE since _start is called before
> >> - 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"
> >> + it is relocated. This also avoid rely on linker optimization to
> >> + transform 'movl main@GOT(%ebx), %eax' to 'leal main@GOTOFF(%ebx)'
> >> if main is defined locally. */
> >> - movl main@GOT(%ebx), %eax
> >> + leal __wrap_main@GOTOFF(%ebx), %eax
> >> pushl %eax
> >> # endif
> >>
> >> @@ -130,6 +129,12 @@ ENTRY (_start)
> >> 1: movl (%esp), %ebx
> >> ret
> >> #endif
> >> +
> >> +#if defined PIC && !defined SHARED
> >> +__wrap_main:
> >> + _CET_ENDBR
> >> + jmp main
> >
> > Shouldn't it be "jmp main@PLT"?
>
> My understanding is for static build we can handle main as hidden, so there
> is no need use a PLT relocation here.
The original comments have
it is relocated. Don't use "leal main@GOTOFF(%ebx), %eax"
since main may be in a shared object. Linker will convert
If this is only used for static build, we can use "leal
main@GOTOFF(%ebx), %eax".
On 17/11/22 13:52, H.J. Lu wrote:
> On Thu, Nov 17, 2022 at 8:42 AM Adhemerval Zanella Netto
> <adhemerval.zanella@linaro.org> wrote:
>>
>>
>>
>> On 17/11/22 13:07, H.J. Lu wrote:
>>> On Thu, Nov 17, 2022 at 4:43 AM Adhemerval Zanella
>>> <adhemerval.zanella@linaro.org> wrote:
>>>>
>>>> lld does not implement all the linker optimization to avoid the GOT
>>>> relocation as done by binutils (bfd/elf32-i386.c:elf_i386_convert_load_reloc).
>>>> The current 'movl main@GOT(%ebx), %eax' will then create a GOT
>>>> relocation when building with lld, which make static-pie status to
>>>> not being able to start the provided main function.
>>>>
>>>> The change uses a __wrap_main local symbol, which in turn calls main
>>>> (similar as used by aarch64 and s390x).
>>>>
>>>> Checked on i686-linux-gnu with binutils and lld.
>>>> ---
>>>> sysdeps/i386/start.S | 13 +++++++++----
>>>> 1 file changed, 9 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/sysdeps/i386/start.S b/sysdeps/i386/start.S
>>>> index 4ec04bdfd7..d593c4de00 100644
>>>> --- a/sysdeps/i386/start.S
>>>> +++ b/sysdeps/i386/start.S
>>>> @@ -98,11 +98,10 @@ ENTRY (_start)
>>>> pushl main@GOT(%ebx)
>>>> # else
>>>> /* Avoid relocation in static PIE since _start is called before
>>>> - 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"
>>>> + it is relocated. This also avoid rely on linker optimization to
>>>> + transform 'movl main@GOT(%ebx), %eax' to 'leal main@GOTOFF(%ebx)'
>>>> if main is defined locally. */
>>>> - movl main@GOT(%ebx), %eax
>>>> + 955774751b71c4bc94029dd541ad9d34634ec995 __wrap_main@GOTOFF(%ebx), %eax
>>>> pushl %eax
>>>> # endif
>>>>
>>>> @@ -130,6 +129,12 @@ ENTRY (_start)
>>>> 1: movl (%esp), %ebx
>>>> ret
>>>> #endif
>>>> +
>>>> +#if defined PIC && !defined SHARED
>>>> +__wrap_main:
>>>> + _CET_ENDBR
>>>> + jmp main
>>>
>>> Shouldn't it be "jmp main@PLT"?
>>
>> My understanding is for static build we can handle main as hidden, so there
>> is no need use a PLT relocation here.
>
> The original comments have
>
> it is relocated. Don't use "leal main@GOTOFF(%ebx), %eax"
> since main may be in a shared object. Linker will convert
>
> If this is only used for static build, we can use "leal
> main@GOTOFF(%ebx), %eax".
>
It does not work with binutils (and that's why you installed 955774751b71c4):
$ make test t=elf/tst-main1
[...]
csu/crt1.o(.text+0x1e): unresolvable R_386_GOTOFF relocation against symbol `main'
collect2: error: ld returned 1 exit status
The start.o (PIC and !SHARED) is used for crt1.o. With 'main' requirement, leal
does work for building tst-main1, so maybe one option could to add a .global main
to pull the symbol.
On Thu, Nov 17, 2022 at 9:28 AM Adhemerval Zanella Netto
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> On 17/11/22 13:52, H.J. Lu wrote:
> > On Thu, Nov 17, 2022 at 8:42 AM Adhemerval Zanella Netto
> > <adhemerval.zanella@linaro.org> wrote:
> >>
> >>
> >>
> >> On 17/11/22 13:07, H.J. Lu wrote:
> >>> On Thu, Nov 17, 2022 at 4:43 AM Adhemerval Zanella
> >>> <adhemerval.zanella@linaro.org> wrote:
> >>>>
> >>>> lld does not implement all the linker optimization to avoid the GOT
> >>>> relocation as done by binutils (bfd/elf32-i386.c:elf_i386_convert_load_reloc).
> >>>> The current 'movl main@GOT(%ebx), %eax' will then create a GOT
> >>>> relocation when building with lld, which make static-pie status to
> >>>> not being able to start the provided main function.
> >>>>
> >>>> The change uses a __wrap_main local symbol, which in turn calls main
> >>>> (similar as used by aarch64 and s390x).
> >>>>
> >>>> Checked on i686-linux-gnu with binutils and lld.
> >>>> ---
> >>>> sysdeps/i386/start.S | 13 +++++++++----
> >>>> 1 file changed, 9 insertions(+), 4 deletions(-)
> >>>>
> >>>> diff --git a/sysdeps/i386/start.S b/sysdeps/i386/start.S
> >>>> index 4ec04bdfd7..d593c4de00 100644
> >>>> --- a/sysdeps/i386/start.S
> >>>> +++ b/sysdeps/i386/start.S
> >>>> @@ -98,11 +98,10 @@ ENTRY (_start)
> >>>> pushl main@GOT(%ebx)
> >>>> # else
> >>>> /* Avoid relocation in static PIE since _start is called before
> >>>> - 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"
> >>>> + it is relocated. This also avoid rely on linker optimization to
> >>>> + transform 'movl main@GOT(%ebx), %eax' to 'leal main@GOTOFF(%ebx)'
> >>>> if main is defined locally. */
> >>>> - movl main@GOT(%ebx), %eax
> >>>> + 955774751b71c4bc94029dd541ad9d34634ec995 __wrap_main@GOTOFF(%ebx), %eax
> >>>> pushl %eax
> >>>> # endif
> >>>>
> >>>> @@ -130,6 +129,12 @@ ENTRY (_start)
> >>>> 1: movl (%esp), %ebx
> >>>> ret
> >>>> #endif
> >>>> +
> >>>> +#if defined PIC && !defined SHARED
> >>>> +__wrap_main:
> >>>> + _CET_ENDBR
> >>>> + jmp main
> >>>
> >>> Shouldn't it be "jmp main@PLT"?
> >>
> >> My understanding is for static build we can handle main as hidden, so there
> >> is no need use a PLT relocation here.
> >
> > The original comments have
> >
> > it is relocated. Don't use "leal main@GOTOFF(%ebx), %eax"
> > since main may be in a shared object. Linker will convert
> >
> > If this is only used for static build, we can use "leal
> > main@GOTOFF(%ebx), %eax".
> >
>
> It does not work with binutils (and that's why you installed 955774751b71c4):
>
> $ make test t=elf/tst-main1
> [...]
> csu/crt1.o(.text+0x1e): unresolvable R_386_GOTOFF relocation against symbol `main'
> collect2: error: ld returned 1 exit status
>
> The start.o (PIC and !SHARED) is used for crt1.o. With 'main' requirement, leal
> does work for building tst-main1, so maybe one option could to add a .global main
> to pull the symbol.
That is because it is also used for dynamic executables. I think PLT
should be used.
On Nov 17 2022, Adhemerval Zanella via Libc-alpha wrote:
> + it is relocated. This also avoid rely on linker optimization to
avoids relying
@@ -98,11 +98,10 @@ ENTRY (_start)
pushl main@GOT(%ebx)
# else
/* Avoid relocation in static PIE since _start is called before
- 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"
+ it is relocated. This also avoid rely on linker optimization to
+ transform 'movl main@GOT(%ebx), %eax' to 'leal main@GOTOFF(%ebx)'
if main is defined locally. */
- movl main@GOT(%ebx), %eax
+ leal __wrap_main@GOTOFF(%ebx), %eax
pushl %eax
# endif
@@ -130,6 +129,12 @@ ENTRY (_start)
1: movl (%esp), %ebx
ret
#endif
+
+#if defined PIC && !defined SHARED
+__wrap_main:
+ _CET_ENDBR
+ jmp main
+#endif
END (_start)
/* To fulfill the System V/i386 ABI we need this symbol. Yuck, it's so