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(&u.b[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, regs,
cross_endian);
break;
#endif
#ifdef CONFIG_VSX
Is there something that I may be overlooking here? :)
Thanks!
--
Gustavo
