| Message ID | 20220405173632.2663-1-h0tc0d3@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/amdgpu: Senseless code and unnecessary memset | expand |
On Tue, 05 Apr 2022, Christian König <christian.koenig@amd.com> wrote: > Am 05.04.22 um 19:36 schrieb Grigory Vasilyev: >> Using memset on local arrays before exiting the function is pointless. >> Compilator will remove this code. Also for local arrays is preferable to >> use {0} instead of memset. Mistakes are often made when working with >> memset. > > Well actually memset is preferred when working with structures which are > given to the hardware parser because {0} won't initialize paddings. Not that I'd know anything that's going on here... but it sure seems strange to me to be passing unpacked structures where the padding might matter to a "hardware parser". *shrug* BR, Jani. > > So please don't use {0} in any of the atom bios code. > > Regards, > Christian. > >> >> Signed-off-by: Grigory Vasilyev <h0tc0d3@gmail.com> >> --- >> drivers/gpu/drm/amd/amdgpu/atom.c | 8 +------- >> 1 file changed, 1 insertion(+), 7 deletions(-) >> >> diff --git a/drivers/gpu/drm/amd/amdgpu/atom.c b/drivers/gpu/drm/amd/amdgpu/atom.c >> index be9d61bcb8ae..537e48fbbe6b 100644 >> --- a/drivers/gpu/drm/amd/amdgpu/atom.c >> +++ b/drivers/gpu/drm/amd/amdgpu/atom.c >> @@ -1538,11 +1538,9 @@ struct atom_context *amdgpu_atom_parse(struct card_info *card, void *bios) >> int amdgpu_atom_asic_init(struct atom_context *ctx) >> { >> int hwi = CU16(ctx->data_table + ATOM_DATA_FWI_PTR); >> - uint32_t ps[16]; >> + uint32_t ps[16] = {0}; >> int ret; >> >> - memset(ps, 0, 64); >> - >> ps[0] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFSCLK_PTR)); >> ps[1] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFMCLK_PTR)); >> if (!ps[0] || !ps[1]) >> @@ -1551,10 +1549,6 @@ int amdgpu_atom_asic_init(struct atom_context *ctx) >> if (!CU16(ctx->cmd_table + 4 + 2 * ATOM_CMD_INIT)) >> return 1; >> ret = amdgpu_atom_execute_table(ctx, ATOM_CMD_INIT, ps); >> - if (ret) >> - return ret; >> - >> - memset(ps, 0, 64); >> >> return ret; >> } >
Am 06.04.22 um 16:26 schrieb Jani Nikula: > On Tue, 05 Apr 2022, Christian König <christian.koenig@amd.com> wrote: >> Am 05.04.22 um 19:36 schrieb Grigory Vasilyev: >>> Using memset on local arrays before exiting the function is pointless. >>> Compilator will remove this code. Also for local arrays is preferable to >>> use {0} instead of memset. Mistakes are often made when working with >>> memset. >> Well actually memset is preferred when working with structures which are >> given to the hardware parser because {0} won't initialize paddings. > Not that I'd know anything that's going on here... but it sure seems > strange to me to be passing unpacked structures where the padding might > matter to a "hardware parser". Well to me it is an absolute miracle why the heck compilers don't initialize paddings. We had so many ups moments over the years and I really don't see why it should be more optimal to do this. Anyway, the memset() is used intentionally here and I don't really want to change it. What we could do is removing the second superfluous memset and use sizeof() instead of hard coding the size. Regards, Christian. > > *shrug* > > > BR, > Jani. > > >> So please don't use {0} in any of the atom bios code. >> >> Regards, >> Christian. >> >>> Signed-off-by: Grigory Vasilyev <h0tc0d3@gmail.com> >>> --- >>> drivers/gpu/drm/amd/amdgpu/atom.c | 8 +------- >>> 1 file changed, 1 insertion(+), 7 deletions(-) >>> >>> diff --git a/drivers/gpu/drm/amd/amdgpu/atom.c b/drivers/gpu/drm/amd/amdgpu/atom.c >>> index be9d61bcb8ae..537e48fbbe6b 100644 >>> --- a/drivers/gpu/drm/amd/amdgpu/atom.c >>> +++ b/drivers/gpu/drm/amd/amdgpu/atom.c >>> @@ -1538,11 +1538,9 @@ struct atom_context *amdgpu_atom_parse(struct card_info *card, void *bios) >>> int amdgpu_atom_asic_init(struct atom_context *ctx) >>> { >>> int hwi = CU16(ctx->data_table + ATOM_DATA_FWI_PTR); >>> - uint32_t ps[16]; >>> + uint32_t ps[16] = {0}; >>> int ret; >>> >>> - memset(ps, 0, 64); >>> - >>> ps[0] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFSCLK_PTR)); >>> ps[1] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFMCLK_PTR)); >>> if (!ps[0] || !ps[1]) >>> @@ -1551,10 +1549,6 @@ int amdgpu_atom_asic_init(struct atom_context *ctx) >>> if (!CU16(ctx->cmd_table + 4 + 2 * ATOM_CMD_INIT)) >>> return 1; >>> ret = amdgpu_atom_execute_table(ctx, ATOM_CMD_INIT, ps); >>> - if (ret) >>> - return ret; >>> - >>> - memset(ps, 0, 64); >>> >>> return ret; >>> }
Christian König in fact the compiler will very often replace {0} with
a memset call. I don't see a problem using {0} for local arrays with
primitive types.
There should also be no problem with memory alignment. Because the
compiler understands it. Using sizeof is also not a good idea.
More often everyone also makes mistakes with sizeof. It's best to
leave it as is, and there's no errors.
Indeed, when using structures and {0}, errors may occur, but I am not
aware of errors when using primitive types. I also looked at the
amdgpu code and {0} is used in many places.
Also from experience malloc+memset is the most dangerous chain, can
silently damage memory, causing a bunch of subtle problems, and it is
better to replace them with more safe calloc.
Such a problem, for example, was recently found by me in fontconfig
and it crashed intel quartus. Therefore, where possible, I try to
avoid memset.
Regards, Grigory.
ср, 6 апр. 2022 г. в 17:43, Christian König <christian.koenig@amd.com>:
>
> Am 06.04.22 um 16:26 schrieb Jani Nikula:
> > On Tue, 05 Apr 2022, Christian König <christian.koenig@amd.com> wrote:
> >> Am 05.04.22 um 19:36 schrieb Grigory Vasilyev:
> >>> Using memset on local arrays before exiting the function is pointless.
> >>> Compilator will remove this code. Also for local arrays is preferable to
> >>> use {0} instead of memset. Mistakes are often made when working with
> >>> memset.
> >> Well actually memset is preferred when working with structures which are
> >> given to the hardware parser because {0} won't initialize paddings.
> > Not that I'd know anything that's going on here... but it sure seems
> > strange to me to be passing unpacked structures where the padding might
> > matter to a "hardware parser".
>
> Well to me it is an absolute miracle why the heck compilers don't
> initialize paddings.
>
> We had so many ups moments over the years and I really don't see why it
> should be more optimal to do this.
>
> Anyway, the memset() is used intentionally here and I don't really want
> to change it. What we could do is removing the second superfluous memset
> and use sizeof() instead of hard coding the size.
>
> Regards,
> Christian.
>
> >
> > *shrug*
> >
> >
> > BR,
> > Jani.
> >
> >
> >> So please don't use {0} in any of the atom bios code.
> >>
> >> Regards,
> >> Christian.
> >>
> >>> Signed-off-by: Grigory Vasilyev <h0tc0d3@gmail.com>
> >>> ---
> >>> drivers/gpu/drm/amd/amdgpu/atom.c | 8 +-------
> >>> 1 file changed, 1 insertion(+), 7 deletions(-)
> >>>
> >>> diff --git a/drivers/gpu/drm/amd/amdgpu/atom.c b/drivers/gpu/drm/amd/amdgpu/atom.c
> >>> index be9d61bcb8ae..537e48fbbe6b 100644
> >>> --- a/drivers/gpu/drm/amd/amdgpu/atom.c
> >>> +++ b/drivers/gpu/drm/amd/amdgpu/atom.c
> >>> @@ -1538,11 +1538,9 @@ struct atom_context *amdgpu_atom_parse(struct card_info *card, void *bios)
> >>> int amdgpu_atom_asic_init(struct atom_context *ctx)
> >>> {
> >>> int hwi = CU16(ctx->data_table + ATOM_DATA_FWI_PTR);
> >>> - uint32_t ps[16];
> >>> + uint32_t ps[16] = {0};
> >>> int ret;
> >>>
> >>> - memset(ps, 0, 64);
> >>> -
> >>> ps[0] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFSCLK_PTR));
> >>> ps[1] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFMCLK_PTR));
> >>> if (!ps[0] || !ps[1])
> >>> @@ -1551,10 +1549,6 @@ int amdgpu_atom_asic_init(struct atom_context *ctx)
> >>> if (!CU16(ctx->cmd_table + 4 + 2 * ATOM_CMD_INIT))
> >>> return 1;
> >>> ret = amdgpu_atom_execute_table(ctx, ATOM_CMD_INIT, ps);
> >>> - if (ret)
> >>> - return ret;
> >>> -
> >>> - memset(ps, 0, 64);
> >>>
> >>> return ret;
> >>> }
>
diff --git a/drivers/gpu/drm/amd/amdgpu/atom.c b/drivers/gpu/drm/amd/amdgpu/atom.c index be9d61bcb8ae..537e48fbbe6b 100644 --- a/drivers/gpu/drm/amd/amdgpu/atom.c +++ b/drivers/gpu/drm/amd/amdgpu/atom.c @@ -1538,11 +1538,9 @@ struct atom_context *amdgpu_atom_parse(struct card_info *card, void *bios) int amdgpu_atom_asic_init(struct atom_context *ctx) { int hwi = CU16(ctx->data_table + ATOM_DATA_FWI_PTR); - uint32_t ps[16]; + uint32_t ps[16] = {0}; int ret; - memset(ps, 0, 64); - ps[0] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFSCLK_PTR)); ps[1] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFMCLK_PTR)); if (!ps[0] || !ps[1]) @@ -1551,10 +1549,6 @@ int amdgpu_atom_asic_init(struct atom_context *ctx) if (!CU16(ctx->cmd_table + 4 + 2 * ATOM_CMD_INIT)) return 1; ret = amdgpu_atom_execute_table(ctx, ATOM_CMD_INIT, ps); - if (ret) - return ret; - - memset(ps, 0, 64); return ret; }
Using memset on local arrays before exiting the function is pointless. Compilator will remove this code. Also for local arrays is preferable to use {0} instead of memset. Mistakes are often made when working with memset. Signed-off-by: Grigory Vasilyev <h0tc0d3@gmail.com> --- drivers/gpu/drm/amd/amdgpu/atom.c | 8 +------- 1 file changed, 1 insertion(+), 7 deletions(-)