2023-01-22 01:22:15

by Michael.Karcher

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Subject: [PATCH: 1/1] sh4: avoid spurious gcc warning

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 <[email protected]>
---

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)    \


2023-01-22 07:28:34

by Randy Dunlap

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Subject: Re: [PATCH: 1/1] sh4: avoid spurious gcc warning

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 <[email protected]>
> ---
>
> 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 <[email protected]> # 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) \
>

--
~Randy

2023-01-22 12:06:27

by Michael Karcher

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Subject: Re: [PATCH: 1/1] sh4: avoid spurious gcc warning

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 <[email protected]> # 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