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

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Message-ID: <b2781922-d536-453f-b593-880674fc8b01@163.com>
Date: Tue, 7 Jan 2025 20:09:48 +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 19:47, Niklas Cassel wrote:
> On Tue, Jan 07, 2025 at 07:43:26PM +0800, Hans Zhang wrote:
>>
>>
>> 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'
> 
> That error was for your patch that changed bar_size to resource_size_t,
> which is typedefed to phys_addr_t, which can be either 32-bits or 64-bits
> on 32-bit systems (depending on CONFIG_X86_PAE).
> 
> I was suggesting to just change it to u64, so it will unconditionally be
> 64-bits.

Hi Niklas,

The robot has been compiled with CONFIG_PHYS_ADDR_T_64BIT=y, so 
resource_size_t=u64


include/linux/types.h

#ifdef CONFIG_PHYS_ADDR_T_64BIT
typedef u64 phys_addr_t;
#else
typedef u32 phys_addr_t;
#endif

typedef phys_addr_t resource_size_t;


Is my understanding wrong? Could you correct me, please? Thank you very 
much.

config: i386-randconfig-003-20250101 
(https://download.01.org/0day-ci/archive/20250101/202501011917.ugP1ywJV-lkp@intel.com/config)


I compiled it as a KO module for an experiment.
__umoddi3 and __udivdi3 is similar to __udivmoddi4.

u64 bar_size;

iters = bar_size / buf_size;
remain = bar_size % buf_size;

zhb@zhb:/media/zhb/hans/code/kernel_org/hans$ make
make -C /media/zhb/hans/code/kernel_org/linux/ 
M=/media/zhb/hans/code/kernel_org/hans modules
make[1]: Entering directory '/media/zhb/hans/code/kernel_org/linux'
make[2]: Entering directory '/media/zhb/hans/code/kernel_org/hans'
   CC [M]  pci_endpoint_test.o
   MODPOST Module.symvers
ERROR: modpost: "__umoddi3" [pci_endpoint_test.ko] undefined!
ERROR: modpost: "__udivdi3" [pci_endpoint_test.ko] undefined!
make[4]: *** 
[/media/zhb/hans/code/kernel_org/linux/scripts/Makefile.modpost:145: 
Module.symvers] Error 1
make[3]: *** [/media/zhb/hans/code/kernel_org/linux/Makefile:1939: 
modpost] Error 2
make[2]: *** [/media/zhb/hans/code/kernel_org/linux/Makefile:251: 
__sub-make] Error 2
make[2]: Leaving directory '/media/zhb/hans/code/kernel_org/hans'
make[1]: *** [Makefile:251: __sub-make] Error 2
make[1]: Leaving directory '/media/zhb/hans/code/kernel_org/linux'
make: *** [Makefile:10: kernel_modules] Error 2


Best regards
Hans