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

[Hans Zhang]

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@xxxxxxx/
> >
> > 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@xxxxxxxxx/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