Re: [RFC - is this a bug?] powerpc/lib/sstep: Asking for some light on this, please. :)
"Gustavo A. R. Silva" writes:
> On 11/20/23 09:21, Naveen N Rao wrote:
>> On Mon, Nov 20, 2023 at 08:33:45AM -0600, Gustavo A. R. Silva wrote:
>>> On 11/20/23 08:25, Naveen N Rao wrote:
On Fri, Nov 17, 2023 at 12:36:01PM -0600, Gustavo A. R. Silva wrote:
> Hi all,
>
> I'm trying to fix the following -Wstringop-overflow warnings, and I'd like
> to get your feedback on this, please:
>
> In function 'do_byte_reverse',
> inlined from 'do_vec_store' at
> /home/gus/linux/arch/powerpc/lib/sstep.c:722:3,
> inlined from 'emulate_loadstore' at
> /home/gus/linux/arch/powerpc/lib/sstep.c:3510:9:
> arch/powerpc/lib/sstep.c:287:23: error: writing 8 bytes into a region of
> size 0 [-Werror=stringop-overflow=]
> 287 | up[3] = tmp;
> | ~~^
> arch/powerpc/lib/sstep.c: In function 'emulate_loadstore':
> arch/powerpc/lib/sstep.c:708:11: note: at offset [24, 39] into
> destination object 'u' of size 16
> 708 | } u;
> | ^
> In function 'do_byte_reverse',
> inlined from 'do_vec_store' at
> /home/gus/linux/arch/powerpc/lib/sstep.c:722:3,
> inlined from 'emulate_loadstore' at
> /home/gus/linux/arch/powerpc/lib/sstep.c:3510:9:
> arch/powerpc/lib/sstep.c:289:23: error: writing 8 bytes into a region of
> size 0 [-Werror=stringop-overflow=]
> 289 | up[2] = byterev_8(up[1]);
> | ~~^~
> arch/powerpc/lib/sstep.c: In function 'emulate_loadstore':
> arch/powerpc/lib/sstep.c:708:11: note: at offset 16 into destination
> object 'u' of size 16
> 708 | } u;
> | ^
> In function 'do_byte_reverse',
> inlined from 'do_vec_load' at
> /home/gus/linux/arch/powerpc/lib/sstep.c:691:3,
> inlined from 'emulate_loadstore' at
> /home/gus/linux/arch/powerpc/lib/sstep.c:3439:9:
> arch/powerpc/lib/sstep.c:287:23: error: writing 8 bytes into a region of
> size 0 [-Werror=stringop-overflow=]
> 287 | up[3] = tmp;
> | ~~^
> arch/powerpc/lib/sstep.c: In function 'emulate_loadstore':
> arch/powerpc/lib/sstep.c:681:11: note: at offset [24, 39] into
> destination object 'u' of size 16
> 681 | } u = {};
> | ^
> arch/powerpc/lib/sstep.c:681:11: note: at offset [24, 39] into
> destination object 'u' of size 16
> arch/powerpc/lib/sstep.c:681:11: note: at offset [24, 39] into
> destination object 'u' of size 16
>
> The origing of the issue seems to be the following calls to function
> `do_vec_store()`, when
> `size > 16`, or more precisely when `size == 32`
>
> arch/powerpc/lib/sstep.c:
> 3436 case LOAD_VMX:
> 3437 if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_VEC))
> 3438 return 0;
> 3439 err = do_vec_load(op->reg, ea, size, regs,
> cross_endian);
> 3440 break;
> ...
> 3507 case STORE_VMX:
> 3508 if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_VEC))
> 3509 return 0;
> 3510 err = do_vec_store(op->reg, ea, size, regs,
> cross_endian);
> 3511 break;
LOAD_VMX and STORE_VMX are set in analyse_instr() and size does not
exceed 16. So, the warning looks incorrect to me.
>>>
>>> Does that mean that this piece of code is never actually executed:
>>>
>>> 281 case 32: {
>>> 282 unsigned long *up = (unsigned long *)ptr;
>>> 283 unsigned long tmp;
>>> 284
>>> 285 tmp = byterev_8(up[0]);
>>> 286 up[0] = byterev_8(up[3]);
>>> 287 up[3] = tmp;
>>> 288 tmp = byterev_8(up[2]);
>>> 289 up[2] = byterev_8(up[1]);
>>> 290 up[1] = tmp;
>>> 291 break;
>>> 292 }
>>>
>>> or rather, under which conditions the above code is executed, if any?
>>
>> Please see git history to understand the commit that introduced that
>> code. You can do that by starting with a 'git blame' on the file. You'll
>> find that the commit that introduced the above hunk was af99da74333b
>> ("powerpc/sstep: Support VSX vector paired storage access
>> instructions").
>>
>> The above code path is hit via
>> do_vsx_load()->emulate_vsx_load()->do_byte_reverse()
>
> It seems there is another path (at least the one that triggers the
> -Wstringop-overflow warnings):
>
> emulate_step()->emulate_loadstore()->do_vec_load()->do_byte_reverse()
>
> emulate_step() {
> ...
> if (OP_IS_LOAD_STORE(type)) {
The type comes from the op, which is determined in analyse_instr()
> err =
Re: [RFC - is this a bug?] powerpc/lib/sstep: Asking for some light on this, please. :)
On 11/20/23 09:21, Naveen N Rao wrote:
On Mon, Nov 20, 2023 at 08:33:45AM -0600, Gustavo A. R. Silva wrote:
On 11/20/23 08:25, Naveen N Rao wrote:
On Fri, Nov 17, 2023 at 12:36:01PM -0600, Gustavo A. R. Silva wrote:
Hi all,
I'm trying to fix the following -Wstringop-overflow warnings, and I'd like
to get your feedback on this, please:
In function 'do_byte_reverse',
inlined from 'do_vec_store' at
/home/gus/linux/arch/powerpc/lib/sstep.c:722:3,
inlined from 'emulate_loadstore' at
/home/gus/linux/arch/powerpc/lib/sstep.c:3510:9:
arch/powerpc/lib/sstep.c:287:23: error: writing 8 bytes into a region of size 0
[-Werror=stringop-overflow=]
287 | up[3] = tmp;
| ~~^
arch/powerpc/lib/sstep.c: In function 'emulate_loadstore':
arch/powerpc/lib/sstep.c:708:11: note: at offset [24, 39] into destination
object 'u' of size 16
708 | } u;
| ^
In function 'do_byte_reverse',
inlined from 'do_vec_store' at
/home/gus/linux/arch/powerpc/lib/sstep.c:722:3,
inlined from 'emulate_loadstore' at
/home/gus/linux/arch/powerpc/lib/sstep.c:3510:9:
arch/powerpc/lib/sstep.c:289:23: error: writing 8 bytes into a region of size 0
[-Werror=stringop-overflow=]
289 | up[2] = byterev_8(up[1]);
| ~~^~
arch/powerpc/lib/sstep.c: In function 'emulate_loadstore':
arch/powerpc/lib/sstep.c:708:11: note: at offset 16 into destination object 'u'
of size 16
708 | } u;
| ^
In function 'do_byte_reverse',
inlined from 'do_vec_load' at
/home/gus/linux/arch/powerpc/lib/sstep.c:691:3,
inlined from 'emulate_loadstore' at
/home/gus/linux/arch/powerpc/lib/sstep.c:3439:9:
arch/powerpc/lib/sstep.c:287:23: error: writing 8 bytes into a region of size 0
[-Werror=stringop-overflow=]
287 | up[3] = tmp;
| ~~^
arch/powerpc/lib/sstep.c: In function 'emulate_loadstore':
arch/powerpc/lib/sstep.c:681:11: note: at offset [24, 39] into destination
object 'u' of size 16
681 | } u = {};
| ^
arch/powerpc/lib/sstep.c:681:11: note: at offset [24, 39] into destination
object 'u' of size 16
arch/powerpc/lib/sstep.c:681:11: note: at offset [24, 39] into destination
object 'u' of size 16
The origing of the issue seems to be the following calls to function
`do_vec_store()`, when
`size > 16`, or more precisely when `size == 32`
arch/powerpc/lib/sstep.c:
3436 case LOAD_VMX:
3437 if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_VEC))
3438 return 0;
3439 err = do_vec_load(op->reg, ea, size, regs, cross_endian);
3440 break;
...
3507 case STORE_VMX:
3508 if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_VEC))
3509 return 0;
3510 err = do_vec_store(op->reg, ea, size, regs, cross_endian);
3511 break;
LOAD_VMX and STORE_VMX are set in analyse_instr() and size does not
exceed 16. So, the warning looks incorrect to me.
Does that mean that this piece of code is never actually executed:
281 case 32: {
282 unsigned long *up = (unsigned long *)ptr;
283 unsigned long tmp;
284
285 tmp = byterev_8(up[0]);
286 up[0] = byterev_8(up[3]);
287 up[3] = tmp;
288 tmp = byterev_8(up[2]);
289 up[2] = byterev_8(up[1]);
290 up[1] = tmp;
291 break;
292 }
or rather, under which conditions the above code is executed, if any?
Please see git history to understand the commit that introduced that
code. You can do that by starting with a 'git blame' on the file. You'll
find that the commit that introduced the above hunk was af99da74333b
("powerpc/sstep: Support VSX vector paired storage access
instructions").
The above code path is hit via
do_vsx_load()->emulate_vsx_load()->do_byte_reverse()
It seems there is another path (at least the one that triggers the
-Wstringop-overflow warnings):
emulate_step()->emulate_loadstore()->do_vec_load()->do_byte_reverse()
emulate_step() {
...
if (OP_IS_LOAD_STORE(type)) {
err = emulate_loadstore(regs, );
if (err)
return 0;
goto instr_done;
}
...
}
> emulate_loadstore() {
...
#ifdef CONFIG_ALTIVEC
case LOAD_VMX:
if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_VEC))
return 0;
err = do_vec_load(op->reg, ea, size, regs, cross_endian); //
with size == 32
break;
#endif
...
#ifdef CONFIG_ALTIVEC
case STORE_VMX:
if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_VEC))
return 0;
err = do_vec_store(op->reg, ea, size,
Re: [RFC - is this a bug?] powerpc/lib/sstep: Asking for some light on this, please. :)
On Mon, Nov 20, 2023 at 08:33:45AM -0600, Gustavo A. R. Silva wrote:
>
>
> On 11/20/23 08:25, Naveen N Rao wrote:
> > On Fri, Nov 17, 2023 at 12:36:01PM -0600, Gustavo A. R. Silva wrote:
> > > Hi all,
> > >
> > > I'm trying to fix the following -Wstringop-overflow warnings, and I'd like
> > > to get your feedback on this, please:
> > >
> > > In function 'do_byte_reverse',
> > > inlined from 'do_vec_store' at
> > > /home/gus/linux/arch/powerpc/lib/sstep.c:722:3,
> > > inlined from 'emulate_loadstore' at
> > > /home/gus/linux/arch/powerpc/lib/sstep.c:3510:9:
> > > arch/powerpc/lib/sstep.c:287:23: error: writing 8 bytes into a region of
> > > size 0 [-Werror=stringop-overflow=]
> > >287 | up[3] = tmp;
> > >| ~~^
> > > arch/powerpc/lib/sstep.c: In function 'emulate_loadstore':
> > > arch/powerpc/lib/sstep.c:708:11: note: at offset [24, 39] into
> > > destination object 'u' of size 16
> > >708 | } u;
> > >| ^
> > > In function 'do_byte_reverse',
> > > inlined from 'do_vec_store' at
> > > /home/gus/linux/arch/powerpc/lib/sstep.c:722:3,
> > > inlined from 'emulate_loadstore' at
> > > /home/gus/linux/arch/powerpc/lib/sstep.c:3510:9:
> > > arch/powerpc/lib/sstep.c:289:23: error: writing 8 bytes into a region of
> > > size 0 [-Werror=stringop-overflow=]
> > >289 | up[2] = byterev_8(up[1]);
> > >| ~~^~
> > > arch/powerpc/lib/sstep.c: In function 'emulate_loadstore':
> > > arch/powerpc/lib/sstep.c:708:11: note: at offset 16 into destination
> > > object 'u' of size 16
> > >708 | } u;
> > >| ^
> > > In function 'do_byte_reverse',
> > > inlined from 'do_vec_load' at
> > > /home/gus/linux/arch/powerpc/lib/sstep.c:691:3,
> > > inlined from 'emulate_loadstore' at
> > > /home/gus/linux/arch/powerpc/lib/sstep.c:3439:9:
> > > arch/powerpc/lib/sstep.c:287:23: error: writing 8 bytes into a region of
> > > size 0 [-Werror=stringop-overflow=]
> > >287 | up[3] = tmp;
> > >| ~~^
> > > arch/powerpc/lib/sstep.c: In function 'emulate_loadstore':
> > > arch/powerpc/lib/sstep.c:681:11: note: at offset [24, 39] into
> > > destination object 'u' of size 16
> > >681 | } u = {};
> > >| ^
> > > arch/powerpc/lib/sstep.c:681:11: note: at offset [24, 39] into
> > > destination object 'u' of size 16
> > > arch/powerpc/lib/sstep.c:681:11: note: at offset [24, 39] into
> > > destination object 'u' of size 16
> > >
> > > The origing of the issue seems to be the following calls to function
> > > `do_vec_store()`, when
> > > `size > 16`, or more precisely when `size == 32`
> > >
> > > arch/powerpc/lib/sstep.c:
> > > 3436 case LOAD_VMX:
> > > 3437 if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_VEC))
> > > 3438 return 0;
> > > 3439 err = do_vec_load(op->reg, ea, size, regs,
> > > cross_endian);
> > > 3440 break;
> > > ...
> > > 3507 case STORE_VMX:
> > > 3508 if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_VEC))
> > > 3509 return 0;
> > > 3510 err = do_vec_store(op->reg, ea, size, regs,
> > > cross_endian);
> > > 3511 break;
> >
> > LOAD_VMX and STORE_VMX are set in analyse_instr() and size does not
> > exceed 16. So, the warning looks incorrect to me.
>
> Does that mean that this piece of code is never actually executed:
>
> 281 case 32: {
> 282 unsigned long *up = (unsigned long *)ptr;
> 283 unsigned long tmp;
> 284
> 285 tmp = byterev_8(up[0]);
> 286 up[0] = byterev_8(up[3]);
> 287 up[3] = tmp;
> 288 tmp = byterev_8(up[2]);
> 289 up[2] = byterev_8(up[1]);
> 290 up[1] = tmp;
> 291 break;
> 292 }
>
> or rather, under which conditions the above code is executed, if any?
Please see git history to understand the commit that introduced that
code. You can do that by starting with a 'git blame' on the file. You'll
find that the commit that introduced the above hunk was af99da74333b
("powerpc/sstep: Support VSX vector paired storage access
instructions").
The above code path is hit via
do_vsx_load()->emulate_vsx_load()->do_byte_reverse()
- Naveen
Re: [RFC - is this a bug?] powerpc/lib/sstep: Asking for some light on this, please. :)
On 11/20/23 08:25, Naveen N Rao wrote:
On Fri, Nov 17, 2023 at 12:36:01PM -0600, Gustavo A. R. Silva wrote:
Hi all,
I'm trying to fix the following -Wstringop-overflow warnings, and I'd like
to get your feedback on this, please:
In function 'do_byte_reverse',
inlined from 'do_vec_store' at
/home/gus/linux/arch/powerpc/lib/sstep.c:722:3,
inlined from 'emulate_loadstore' at
/home/gus/linux/arch/powerpc/lib/sstep.c:3510:9:
arch/powerpc/lib/sstep.c:287:23: error: writing 8 bytes into a region of size 0
[-Werror=stringop-overflow=]
287 | up[3] = tmp;
| ~~^
arch/powerpc/lib/sstep.c: In function 'emulate_loadstore':
arch/powerpc/lib/sstep.c:708:11: note: at offset [24, 39] into destination
object 'u' of size 16
708 | } u;
| ^
In function 'do_byte_reverse',
inlined from 'do_vec_store' at
/home/gus/linux/arch/powerpc/lib/sstep.c:722:3,
inlined from 'emulate_loadstore' at
/home/gus/linux/arch/powerpc/lib/sstep.c:3510:9:
arch/powerpc/lib/sstep.c:289:23: error: writing 8 bytes into a region of size 0
[-Werror=stringop-overflow=]
289 | up[2] = byterev_8(up[1]);
| ~~^~
arch/powerpc/lib/sstep.c: In function 'emulate_loadstore':
arch/powerpc/lib/sstep.c:708:11: note: at offset 16 into destination object 'u'
of size 16
708 | } u;
| ^
In function 'do_byte_reverse',
inlined from 'do_vec_load' at
/home/gus/linux/arch/powerpc/lib/sstep.c:691:3,
inlined from 'emulate_loadstore' at
/home/gus/linux/arch/powerpc/lib/sstep.c:3439:9:
arch/powerpc/lib/sstep.c:287:23: error: writing 8 bytes into a region of size 0
[-Werror=stringop-overflow=]
287 | up[3] = tmp;
| ~~^
arch/powerpc/lib/sstep.c: In function 'emulate_loadstore':
arch/powerpc/lib/sstep.c:681:11: note: at offset [24, 39] into destination
object 'u' of size 16
681 | } u = {};
| ^
arch/powerpc/lib/sstep.c:681:11: note: at offset [24, 39] into destination
object 'u' of size 16
arch/powerpc/lib/sstep.c:681:11: note: at offset [24, 39] into destination
object 'u' of size 16
The origing of the issue seems to be the following calls to function
`do_vec_store()`, when
`size > 16`, or more precisely when `size == 32`
arch/powerpc/lib/sstep.c:
3436 case LOAD_VMX:
3437 if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_VEC))
3438 return 0;
3439 err = do_vec_load(op->reg, ea, size, regs, cross_endian);
3440 break;
...
3507 case STORE_VMX:
3508 if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_VEC))
3509 return 0;
3510 err = do_vec_store(op->reg, ea, size, regs, cross_endian);
3511 break;
LOAD_VMX and STORE_VMX are set in analyse_instr() and size does not
exceed 16. So, the warning looks incorrect to me.
Does that mean that this piece of code is never actually executed:
281 case 32: {
282 unsigned long *up = (unsigned long *)ptr;
283 unsigned long tmp;
284
285 tmp = byterev_8(up[0]);
286 up[0] = byterev_8(up[3]);
287 up[3] = tmp;
288 tmp = byterev_8(up[2]);
289 up[2] = byterev_8(up[1]);
290 up[1] = tmp;
291 break;
292 }
or rather, under which conditions the above code is executed, if any?
Thanks!
--
Gustavo
Re: [RFC - is this a bug?] powerpc/lib/sstep: Asking for some light on this, please. :)
On Fri, Nov 17, 2023 at 12:36:01PM -0600, Gustavo A. R. Silva wrote:
> Hi all,
>
> I'm trying to fix the following -Wstringop-overflow warnings, and I'd like
> to get your feedback on this, please:
>
> In function 'do_byte_reverse',
> inlined from 'do_vec_store' at
> /home/gus/linux/arch/powerpc/lib/sstep.c:722:3,
> inlined from 'emulate_loadstore' at
> /home/gus/linux/arch/powerpc/lib/sstep.c:3510:9:
> arch/powerpc/lib/sstep.c:287:23: error: writing 8 bytes into a region of size
> 0 [-Werror=stringop-overflow=]
> 287 | up[3] = tmp;
> | ~~^
> arch/powerpc/lib/sstep.c: In function 'emulate_loadstore':
> arch/powerpc/lib/sstep.c:708:11: note: at offset [24, 39] into destination
> object 'u' of size 16
> 708 | } u;
> | ^
> In function 'do_byte_reverse',
> inlined from 'do_vec_store' at
> /home/gus/linux/arch/powerpc/lib/sstep.c:722:3,
> inlined from 'emulate_loadstore' at
> /home/gus/linux/arch/powerpc/lib/sstep.c:3510:9:
> arch/powerpc/lib/sstep.c:289:23: error: writing 8 bytes into a region of size
> 0 [-Werror=stringop-overflow=]
> 289 | up[2] = byterev_8(up[1]);
> | ~~^~
> arch/powerpc/lib/sstep.c: In function 'emulate_loadstore':
> arch/powerpc/lib/sstep.c:708:11: note: at offset 16 into destination object
> 'u' of size 16
> 708 | } u;
> | ^
> In function 'do_byte_reverse',
> inlined from 'do_vec_load' at
> /home/gus/linux/arch/powerpc/lib/sstep.c:691:3,
> inlined from 'emulate_loadstore' at
> /home/gus/linux/arch/powerpc/lib/sstep.c:3439:9:
> arch/powerpc/lib/sstep.c:287:23: error: writing 8 bytes into a region of size
> 0 [-Werror=stringop-overflow=]
> 287 | up[3] = tmp;
> | ~~^
> arch/powerpc/lib/sstep.c: In function 'emulate_loadstore':
> arch/powerpc/lib/sstep.c:681:11: note: at offset [24, 39] into destination
> object 'u' of size 16
> 681 | } u = {};
> | ^
> arch/powerpc/lib/sstep.c:681:11: note: at offset [24, 39] into destination
> object 'u' of size 16
> arch/powerpc/lib/sstep.c:681:11: note: at offset [24, 39] into destination
> object 'u' of size 16
>
> The origing of the issue seems to be the following calls to function
> `do_vec_store()`, when
> `size > 16`, or more precisely when `size == 32`
>
> arch/powerpc/lib/sstep.c:
> 3436 case LOAD_VMX:
> 3437 if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_VEC))
> 3438 return 0;
> 3439 err = do_vec_load(op->reg, ea, size, regs, cross_endian);
> 3440 break;
> ...
> 3507 case STORE_VMX:
> 3508 if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_VEC))
> 3509 return 0;
> 3510 err = do_vec_store(op->reg, ea, size, regs,
> cross_endian);
> 3511 break;
LOAD_VMX and STORE_VMX are set in analyse_instr() and size does not
exceed 16. So, the warning looks incorrect to me.
- Naveen
[RFC - is this a bug?] powerpc/lib/sstep: Asking for some light on this, please. :)
Hi all,
I'm trying to fix the following -Wstringop-overflow warnings, and I'd like
to get your feedback on this, please:
In function 'do_byte_reverse',
inlined from 'do_vec_store' at
/home/gus/linux/arch/powerpc/lib/sstep.c:722:3,
inlined from 'emulate_loadstore' at
/home/gus/linux/arch/powerpc/lib/sstep.c:3510:9:
arch/powerpc/lib/sstep.c:287:23: error: writing 8 bytes into a region of size 0
[-Werror=stringop-overflow=]
287 | up[3] = tmp;
| ~~^
arch/powerpc/lib/sstep.c: In function 'emulate_loadstore':
arch/powerpc/lib/sstep.c:708:11: note: at offset [24, 39] into destination
object 'u' of size 16
708 | } u;
| ^
In function 'do_byte_reverse',
inlined from 'do_vec_store' at
/home/gus/linux/arch/powerpc/lib/sstep.c:722:3,
inlined from 'emulate_loadstore' at
/home/gus/linux/arch/powerpc/lib/sstep.c:3510:9:
arch/powerpc/lib/sstep.c:289:23: error: writing 8 bytes into a region of size 0
[-Werror=stringop-overflow=]
289 | up[2] = byterev_8(up[1]);
| ~~^~
arch/powerpc/lib/sstep.c: In function 'emulate_loadstore':
arch/powerpc/lib/sstep.c:708:11: note: at offset 16 into destination object 'u'
of size 16
708 | } u;
| ^
In function 'do_byte_reverse',
inlined from 'do_vec_load' at
/home/gus/linux/arch/powerpc/lib/sstep.c:691:3,
inlined from 'emulate_loadstore' at
/home/gus/linux/arch/powerpc/lib/sstep.c:3439:9:
arch/powerpc/lib/sstep.c:287:23: error: writing 8 bytes into a region of size 0
[-Werror=stringop-overflow=]
287 | up[3] = tmp;
| ~~^
arch/powerpc/lib/sstep.c: In function 'emulate_loadstore':
arch/powerpc/lib/sstep.c:681:11: note: at offset [24, 39] into destination
object 'u' of size 16
681 | } u = {};
| ^
arch/powerpc/lib/sstep.c:681:11: note: at offset [24, 39] into destination
object 'u' of size 16
arch/powerpc/lib/sstep.c:681:11: note: at offset [24, 39] into destination
object 'u' of size 16
The origing of the issue seems to be the following calls to function
`do_vec_store()`, when
`size > 16`, or more precisely when `size == 32`
arch/powerpc/lib/sstep.c:
3436 case LOAD_VMX:
3437 if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_VEC))
3438 return 0;
3439 err = do_vec_load(op->reg, ea, size, regs, cross_endian);
3440 break;
...
3507 case STORE_VMX:
3508 if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_VEC))
3509 return 0;
3510 err = do_vec_store(op->reg, ea, size, regs, cross_endian);
3511 break;
Inside `do_vec_store()`, we have that the size of `union u` is 16 bytes:
702 int size, struct pt_regs *regs,
703 bool cross_endian)
704 {
705 union {
706 __vector128 v;
707 u8 b[sizeof(__vector128)];
708 } u;
and then function `do_byte_reverse()` is called
721 if (unlikely(cross_endian))
722 do_byte_reverse([ea & 0xf], size);
and if `size == 32`, the following piece of code tries to access
`ptr` outside of its boundaries:
260 static nokprobe_inline void do_byte_reverse(void *ptr, int nb)
261 {
262 switch (nb) {
...
281 case 32: {
282 unsigned long *up = (unsigned long *)ptr;
283 unsigned long tmp;
284
285 tmp = byterev_8(up[0]);
286 up[0] = byterev_8(up[3]);
287 up[3] = tmp;
288 tmp = byterev_8(up[2]);
289 up[2] = byterev_8(up[1]);
290 up[1] = tmp;
291 break;
292 }
The following patch is merely a test to illustrate how the value in `size`
initially appears
to influence the warnings:
diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
index a4ab8625061a..86786957b736 100644
--- a/arch/powerpc/lib/sstep.c
+++ b/arch/powerpc/lib/sstep.c
@@ -3436,7 +3436,7 @@ int emulate_loadstore(struct pt_regs *regs, struct
instruction_op *op)
case LOAD_VMX:
if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_VEC))
return 0;
- err = do_vec_load(op->reg, ea, size, regs, cross_endian);
+ err = do_vec_load(op->reg, ea, (size > 16) ? 16 : size, regs,
cross_endian);
break;
#endif
#ifdef CONFIG_VSX
@@ -3507,7 +3507,7 @@ int emulate_loadstore(struct pt_regs *regs, struct
instruction_op *op)
case STORE_VMX:
if (!(regs->msr & MSR_PR) && !(regs->msr & MSR_VEC))
return 0;
- err = do_vec_store(op->reg, ea, size, regs, cross_endian);
+ err = do_vec_store(op->reg, ea, (size > 16) ? 16 : size,
