[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(&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
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
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 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 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, &op); 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, siz
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 = emul