Re: [v8] misc: pci_endpoint_test: Fix overflow of bar_size

[Hans Zhang]

On 2025/1/7 19:33, Niklas Cassel wrote:
> > Hi Niklas,
> >
> > resource_size_t bar_size;
> > remain = do_div((u64)bar_size, buf_size);
> >
> > It works for the arm platform.
> >
> > arch/arm/include/asm/div64.h
> > static inline uint32_t __div64_32(uint64_t *n, uint32_t base)
> > {
> > 	register unsigned int __base      asm("r4") = base;
> > 	register unsigned long long __n   asm("r0") = *n;
> > 	register unsigned long long __res asm("r2");
> > 	unsigned int __rem;
> > 	asm(	__asmeq("%0", "r0")
> > 		__asmeq("%1", "r2")
> > 		__asmeq("%2", "r4")
> > 		"bl	__do_div64"
> > 		: "+r" (__n), "=r" (__res)
> > 		: "r" (__base)
> > 		: "ip", "lr", "cc");
> > 	__rem = __n >> 32;
> > 	*n = __res;
> > 	return __rem;
> > }
> > #define __div64_32 __div64_32
> >
> > #define do_div(n, base) __div64_32(&(n), base)
> >
> >
> > For X86 platforms, do_div is a macro definition, and the first parameter
> > does not define its type. If the macro definition is replaced directly, an
> > error will be reported in the ubuntu20.04 release.
>
> What is the error?
>
> We don't need to use do_div().
> The current code that does normal / and % works fine on both
> 32-bit and 64-bit if you just do:
>
>   static bool pci_endpoint_test_bar(struct pci_endpoint_test *test,
>                                    enum pci_barno barno)
>   {
> -       int j, bar_size, buf_size, iters, remain;
> +       int j, buf_size, iters, remain;
>          void *write_buf __free(kfree) = NULL;
>          void *read_buf __free(kfree) = NULL;
>          struct pci_dev *pdev = test->pdev;
> +       u64 bar_size;
>
> No?


Hi Niklas,

Please look at the robot compilation error.

https://patchwork.kernel.org/project/linux-pci/patch/20241231065500.168799-1-18255117159@xxxxxxx/

drivers/misc/pci_endpoint_test.c:315: undefined reference to `__udivmoddi4'

Best regards
Hans