Messages in this thread Patch in this message | | | Date | Tue, 17 Jan 2023 17:42:37 +0100 | Subject | Calculating array sizes in C - was: Re: Build regressions/improvements in v6.2-rc1 | From | John Paul Adrian Glaubitz <> |
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Hi Geert!
On 1/6/23 16:17, Geert Uytterhoeven wrote: >> I'm not seeing this one, but I am getting this one instead: >> >> In file included from ./arch/sh/include/asm/hw_irq.h:6, >> from ./include/linux/irq.h:596, >> from ./include/asm-generic/hardirq.h:17, >> from ./arch/sh/include/asm/hardirq.h:9, >> from ./include/linux/hardirq.h:11, >> from ./include/linux/interrupt.h:11, >> from ./include/linux/serial_core.h:13, >> from ./include/linux/serial_sci.h:6, >> from arch/sh/kernel/cpu/sh2/setup-sh7619.c:11: >> ./include/linux/sh_intc.h:100:63: error: division 'sizeof (void *) / sizeof (void)' does not compute the number of array elements [-Werror=sizeof-pointer-div] >> 100 | #define _INTC_ARRAY(a) a, __same_type(a, NULL) ? 0 : sizeof(a)/sizeof(*a) >> | ^ >> ./include/linux/sh_intc.h:105:31: note: in expansion of macro '_INTC_ARRAY' >> 105 | _INTC_ARRAY(vectors), _INTC_ARRAY(groups), \ >> | ^~~~~~~~~~~ > > The easiest fix for the latter is to disable CONFIG_WERROR. > Unfortunately I don't know a simple solution to get rid of the warning.
I did some research and it seems that what the macro _INT_ARRAY() does with "sizeof(a)/sizeof(*a)" is a commonly used way to calculate array sizes and the kernel has even its own macro for that called ARRAY_SIZE() which Linus asks people to use here [1].
So, I replaced _INTC_ARRAY() with ARRAY_SIZE() (see below), however the kernel's own ARRAY_SIZE() macro triggers the same compiler warning. I'm CC'ing Michael Karcher who has more knowledge on writing proper C code than me and maybe an idea how to fix this warning.
Thanks, Adrian
> [1] https://lkml.org/lkml/2015/9/3/428
diff --git a/include/linux/sh_intc.h b/include/linux/sh_intc.h index c255273b0281..07a187686a84 100644 --- a/include/linux/sh_intc.h +++ b/include/linux/sh_intc.h @@ -97,14 +97,12 @@ struct intc_hw_desc { unsigned int nr_subgroups; }; -#define _INTC_ARRAY(a) a, __same_type(a, NULL) ? 0 : sizeof(a)/sizeof(*a) - #define INTC_HW_DESC(vectors, groups, mask_regs, \ prio_regs, sense_regs, ack_regs) \ { \ - _INTC_ARRAY(vectors), _INTC_ARRAY(groups), \ - _INTC_ARRAY(mask_regs), _INTC_ARRAY(prio_regs), \ - _INTC_ARRAY(sense_regs), _INTC_ARRAY(ack_regs), \ + ARRAY_SIZE(vectors), ARRAY_SIZE(groups), \ + ARRAY_SIZE(mask_regs), ARRAY_SIZE(prio_regs), \ + ARRAY_SIZE(sense_regs), ARRAY_SIZE(ack_regs), \ } struct intc_desc { -- .''`. John Paul Adrian Glaubitz : :' : Debian Developer `. `' Physicist `- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913
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