linux-kernel - Re: [v8] misc: pci_endpoint_test: Fix overflow of bar

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Message-ID: <270783b7-70c6-49d5-8464-fb542396e2dd@163.com>
Date: Tue, 7 Jan 2025 19:43:26 +0800
From: Hans Zhang <18255117159@....com>
To: Niklas Cassel <cassel@...nel.org>
Cc: manivannan.sadhasivam@...aro.org, kw@...ux.com, kishon@...nel.org,
 arnd@...db.de, gregkh@...uxfoundation.org, linux-pci@...r.kernel.org,
 linux-kernel@...r.kernel.org, rockswang7@...il.com
Subject: Re: [v8] misc: pci_endpoint_test: Fix overflow of bar_size



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@163.com/

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

Best regards
Hans