| Message ID | 52952170-f1a9-89a0-e307-f974ce2b7977@fu-berlin.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [PATCH:,1/1] sh4: avoid spurious gcc warning | expand |
Hi-- It's just sh: AFAICT. The patch fixes the build error for me on sh2, using gcc 12.1.0 from the kernel.org crosstool builds. On 1/21/23 16:15, Michael.Karcher wrote: > Prevent sizeof-pointer-div warning in SH4 intc macros > > Gcc warns about the pattern sizeof(void*)/sizeof(void), as it looks like > the abuse of a pattern to calculate the array size. This pattern appears > in the unevaluated part of the ternary operator in _INTC_ARRAY if the > parameter is NULL. > > The replacement uses an alternate approach to return 0 in case of NULL > which does not generate the pattern sizeof(void*)/sizeof(void), but still > emits the warning if _INTC_ARRAY is called with a nonarray parameter. > > This patch is required for successful compilation with -Werror enabled. > > The idea to use _Generic for type distinction is taken from Comment #7 > in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108483 by Jakub Jelinek > > Signed-off-by: Michael Karcher <kernel@mkarcher.dialup.fu-berlin.de> > --- > > diff --git a/include/linux/sh_intc.h b/include/linux/sh_intc.h > index c255273b0281..d7a7ffb60a34 100644 > --- a/include/linux/sh_intc.h > +++ b/include/linux/sh_intc.h > @@ -97,7 +97,7 @@ struct intc_hw_desc { > unsigned int nr_subgroups; > }; > > -#define _INTC_ARRAY(a) a, __same_type(a, NULL) ? 0 : sizeof(a)/sizeof(*a) > +#define _INTC_ARRAY(a) a, sizeof(a)/(_Generic((a), typeof(NULL): 0xFFFFFFFFU, default: sizeof(*a))) s/: / : / in 2 places. Tested-by: Randy Dunlap <rdunlap@infradead.org> # build-tested How far back in gcc versions does this work? Thanks. > > #define INTC_HW_DESC(vectors, groups, mask_regs, \ > prio_regs, sense_regs, ack_regs) \ >
Am 22.01.2023 um 08:00 schrieb Randy Dunlap: >> -#define _INTC_ARRAY(a) a, __same_type(a, NULL) ? 0 : sizeof(a)/sizeof(*a) >> +#define _INTC_ARRAY(a) a, sizeof(a)/(_Generic((a), typeof(NULL): 0xFFFFFFFFU, default: sizeof(*a))) > s/: / : / in 2 places. > > Tested-by: Randy Dunlap <rdunlap@infradead.org> # build-tested Thanks for your confirmation! Are you sure about the space before the colon? The colon in this case terminates a case descriptor for the type-level switch construction using "_Generic". It says: "In case 'a' has the 'type of NULL', divide by 0xFFFFFFFFU, in all other cases, divide by the size of a single array element". It's not a colon of the ternary ?: operator, in which case I would agree with the space before it. If you confirm that you want a space before the colon in this case as well, I'm going to add it, though. > How far back in gcc versions does this work? I tested the support of _Generic on Compiler Explorer at godbolt.org. This construction is rejected by gcc 4.8, but accepted by gcc 4.9. Kind regards, Michael Karcher
Hi Michael! On 1/22/23 01:15, Michael.Karcher wrote: > Prevent sizeof-pointer-div warning in SH4 intc macros > > Gcc warns about the pattern sizeof(void*)/sizeof(void), as it looks like > the abuse of a pattern to calculate the array size. This pattern appears > in the unevaluated part of the ternary operator in _INTC_ARRAY if the > parameter is NULL. > > The replacement uses an alternate approach to return 0 in case of NULL > which does not generate the pattern sizeof(void*)/sizeof(void), but still > emits the warning if _INTC_ARRAY is called with a nonarray parameter. > > This patch is required for successful compilation with -Werror enabled. > > The idea to use _Generic for type distinction is taken from Comment #7 > in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108483 by Jakub Jelinek > > Signed-off-by: Michael Karcher <kernel@mkarcher.dialup.fu-berlin.de> > --- > > diff --git a/include/linux/sh_intc.h b/include/linux/sh_intc.h > index c255273b0281..d7a7ffb60a34 100644 > --- a/include/linux/sh_intc.h > +++ b/include/linux/sh_intc.h > @@ -97,7 +97,7 @@ struct intc_hw_desc { > unsigned int nr_subgroups; > }; > > -#define _INTC_ARRAY(a) a, __same_type(a, NULL) ? 0 : sizeof(a)/sizeof(*a) > +#define _INTC_ARRAY(a) a, sizeof(a)/(_Generic((a), typeof(NULL): 0xFFFFFFFFU, default: sizeof(*a))) > > #define INTC_HW_DESC(vectors, groups, mask_regs, \ > prio_regs, sense_regs, ack_regs) \ The title should probably be "arch/sh: avoid spurious gcc warning" since it's not a problem special to sh4 but affects the whole arch/sh sub-folder which covers all SuperH and J-Core targets. Can you rephrase the title accordingly? Adrian
On Sun, Jan 22, 2023 at 12:33:41PM +0100, Michael Karcher wrote: > Am 22.01.2023 um 08:00 schrieb Randy Dunlap: > > > -#define _INTC_ARRAY(a) a, __same_type(a, NULL) ? 0 : sizeof(a)/sizeof(*a) > > > +#define _INTC_ARRAY(a) a, sizeof(a)/(_Generic((a), typeof(NULL): 0xFFFFFFFFU, default: sizeof(*a))) > > s/: / : / in 2 places. > > > > Tested-by: Randy Dunlap <rdunlap@infradead.org> # build-tested > > Thanks for your confirmation! Are you sure about the space before the colon? No, it should be without those, see various other _Generic uses in include/linux/ All those are formatted on one line for each case, so for the above macro it would be #define _INTC_ARRAY(a) (a), sizeof(a)/(_Generic((a), \ typeof(NULL): -1, \ default: sizeof(*(a))) or so. Anyway, two comments: 1) I'd use -1 as that would be after promotion to size_t the largest size_t unlike 0xFFFFFFFFU; of course, as for the void * case a can't be an array, any value > sizeof(void*) will do 2) if *a and a is fine (i.e. argument of the macro has to be really simple or wrapped in ()s, then perhaps (a) as first operand to _Generic isn't needed either, or use (a) in the two spots (sizeof(a) is of course fine) and *(a) > The colon in this case terminates a case descriptor for the type-level > switch construction using "_Generic". It says: "In case 'a' has the 'type of > NULL', divide by 0xFFFFFFFFU, in all other cases, divide by the size of a > single array element". It's not a colon of the ternary ?: operator, in which > case I would agree with the space before it. > > If you confirm that you want a space before the colon in this case as well, > I'm going to add it, though. > > > How far back in gcc versions does this work? > > I tested the support of _Generic on Compiler Explorer at godbolt.org. This > construction is rejected by gcc 4.8, but accepted by gcc 4.9. Yeah, introduced in gcc 4.9, as I think kernel minimum version is 5.1, that is fine. And various headers already use _Generic. Jakub
On 1/22/23 04:42, Jakub Jelinek wrote: > On Sun, Jan 22, 2023 at 12:33:41PM +0100, Michael Karcher wrote: >> Am 22.01.2023 um 08:00 schrieb Randy Dunlap: >>>> -#define _INTC_ARRAY(a) a, __same_type(a, NULL) ? 0 : sizeof(a)/sizeof(*a) >>>> +#define _INTC_ARRAY(a) a, sizeof(a)/(_Generic((a), typeof(NULL): 0xFFFFFFFFU, default: sizeof(*a))) >>> s/: / : / in 2 places. >>> >>> Tested-by: Randy Dunlap <rdunlap@infradead.org> # build-tested >> >> Thanks for your confirmation! Are you sure about the space before the colon? Nope, my bad. Thanks, Jakub. > No, it should be without those, see various other _Generic uses in > include/linux/ > All those are formatted on one line for each case, so for the above macro it > would be > #define _INTC_ARRAY(a) (a), sizeof(a)/(_Generic((a), \ > typeof(NULL): -1, \ > default: sizeof(*(a))) > or so. > Anyway, two comments: > 1) I'd use -1 as that would be after promotion to size_t the largest size_t > unlike 0xFFFFFFFFU; of course, as for the void * case a can't be an array, > any value > sizeof(void*) will do > 2) if *a and a is fine (i.e. argument of the macro has to be really simple or > wrapped in ()s, then perhaps (a) as first operand to _Generic isn't needed > either, or use (a) in the two spots (sizeof(a) is of course fine) and > *(a) > >> The colon in this case terminates a case descriptor for the type-level >> switch construction using "_Generic". It says: "In case 'a' has the 'type of >> NULL', divide by 0xFFFFFFFFU, in all other cases, divide by the size of a >> single array element". It's not a colon of the ternary ?: operator, in which >> case I would agree with the space before it. >> >> If you confirm that you want a space before the colon in this case as well, >> I'm going to add it, though. >> >>> How far back in gcc versions does this work? >> >> I tested the support of _Generic on Compiler Explorer at godbolt.org. This >> construction is rejected by gcc 4.8, but accepted by gcc 4.9. > > Yeah, introduced in gcc 4.9, as I think kernel minimum version is 5.1, that is fine. > And various headers already use _Generic. and thanks for that info also.
Hi Jakub, On Sun, Jan 22, 2023 at 1:47 PM Jakub Jelinek <jakub@redhat.com> wrote: > On Sun, Jan 22, 2023 at 12:33:41PM +0100, Michael Karcher wrote: > > Am 22.01.2023 um 08:00 schrieb Randy Dunlap: > > > > -#define _INTC_ARRAY(a) a, __same_type(a, NULL) ? 0 : sizeof(a)/sizeof(*a) > > > > +#define _INTC_ARRAY(a) a, sizeof(a)/(_Generic((a), typeof(NULL): 0xFFFFFFFFU, default: sizeof(*a))) > > > s/: / : / in 2 places. > > > > > > Tested-by: Randy Dunlap <rdunlap@infradead.org> # build-tested > > > > Thanks for your confirmation! Are you sure about the space before the colon? > > No, it should be without those, see various other _Generic uses in > include/linux/ > All those are formatted on one line for each case, so for the above macro it > would be > #define _INTC_ARRAY(a) (a), sizeof(a)/(_Generic((a), \ > typeof(NULL): -1, \ > default: sizeof(*(a))) > or so. > Anyway, two comments: > 1) I'd use -1 as that would be after promotion to size_t the largest size_t > unlike 0xFFFFFFFFU; of course, as for the void * case a can't be an array, > any value > sizeof(void*) will do Or SIZE_MAX. include/linux/limits.h:#define SIZE_MAX (~(size_t)0) Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
On Mon, Jan 23, 2023 at 04:06:27PM +0000, David Laight wrote: > From: Michael.Karcher > > Sent: 22 January 2023 00:15 > > > > Prevent sizeof-pointer-div warning in SH4 intc macros > > > > Gcc warns about the pattern sizeof(void*)/sizeof(void), as it looks like > > the abuse of a pattern to calculate the array size. This pattern appears > > in the unevaluated part of the ternary operator in _INTC_ARRAY if the > > parameter is NULL. > > > > The replacement uses an alternate approach to return 0 in case of NULL > > which does not generate the pattern sizeof(void*)/sizeof(void), but still > > emits the warning if _INTC_ARRAY is called with a nonarray parameter. > > > > This patch is required for successful compilation with -Werror enabled. > > > > The idea to use _Generic for type distinction is taken from Comment #7 > > in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108483 by Jakub Jelinek > > > > Signed-off-by: Michael Karcher <kernel@mkarcher.dialup.fu-berlin.de> > > --- > > > > diff --git a/include/linux/sh_intc.h b/include/linux/sh_intc.h > > index c255273b0281..d7a7ffb60a34 100644 > > --- a/include/linux/sh_intc.h > > +++ b/include/linux/sh_intc.h > > @@ -97,7 +97,7 @@ struct intc_hw_desc { > > unsigned int nr_subgroups; > > }; > > > > -#define _INTC_ARRAY(a) a, __same_type(a, NULL) ? 0 : sizeof(a)/sizeof(*a) > > FWIW it is (currently) enough to add 0 to the top or bottom > of the division. If you don't want the warning at all, sure. But if you want the compiler to warn if you use the macro on a (non-void *) pointer rather than array, what has been posted is needed. Jakub
Am 23.01.2023 um 17:11 schrieb Jakub Jelinek: > On Mon, Jan 23, 2023 at 04:06:27PM +0000, David Laight wrote: >> From: Michael.Karcher >>> -#define _INTC_ARRAY(a) a, __same_type(a, NULL) ? 0 : sizeof(a)/sizeof(*a) >> FWIW it is (currently) enough to add 0 to the top or bottom >> of the division. > If you don't want the warning at all, sure. But if you want the compiler > to warn if you use the macro on a (non-void *) pointer rather than array, > what has been posted is needed. Exactly. I actually had sizeof(a)/(sizeof(*a) + 0) at first, but a test showed that it would silently generate invalid code on struct intc_mask_reg singleton = {...}; _INTC_ARRAY(&singleton) If it would expand to "&singleton, 1", it would be fine, but it will expand to "&singleton, 0", as sizeof(intc_mask_reg*) is smaller than sizeof(intc_mask_reg). The version I posted generates the intended warning (upgraded to an error with -Werror) in that case. The old version also generated the intended warning in this case, and not generating a warning here is a regression I didn't want to be responsible for. Kind regards, Michael Karcher
diff --git a/include/linux/sh_intc.h b/include/linux/sh_intc.h index c255273b0281..d7a7ffb60a34 100644 --- a/include/linux/sh_intc.h +++ b/include/linux/sh_intc.h @@ -97,7 +97,7 @@ struct intc_hw_desc { unsigned int nr_subgroups; }; -#define _INTC_ARRAY(a) a, __same_type(a, NULL) ? 0 : sizeof(a)/sizeof(*a) +#define _INTC_ARRAY(a) a, sizeof(a)/(_Generic((a), typeof(NULL): 0xFFFFFFFFU, default: sizeof(*a))) #define INTC_HW_DESC(vectors, groups, mask_regs, \
Prevent sizeof-pointer-div warning in SH4 intc macros Gcc warns about the pattern sizeof(void*)/sizeof(void), as it looks like the abuse of a pattern to calculate the array size. This pattern appears in the unevaluated part of the ternary operator in _INTC_ARRAY if the parameter is NULL. The replacement uses an alternate approach to return 0 in case of NULL which does not generate the pattern sizeof(void*)/sizeof(void), but still emits the warning if _INTC_ARRAY is called with a nonarray parameter. This patch is required for successful compilation with -Werror enabled. The idea to use _Generic for type distinction is taken from Comment #7 in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108483 by Jakub Jelinek Signed-off-by: Michael Karcher <kernel@mkarcher.dialup.fu-berlin.de> --- prio_regs, sense_regs, ack_regs) \