Re: sound/pci/asihpi/hpioctl.c:125:6: warning: cast to pointer from integer of different size

Re: sound/pci/asihpi/hpioctl.c:125:6: warning: cast to pointer from integer of different size

[H. Peter Anvin]

On 02/07/2013 03:45 PM, kbuild test robot wrote:
> tree:   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/mm
> head:   6fcddf474ae1c8e2fb5f14c850c8aa018e7a5034
> commit: 6fcddf474ae1c8e2fb5f14c850c8aa018e7a5034 x86-32: Add support for 64bit get_user()
> date:   2 hours ago
> config: make ARCH=i386 allmodconfig
> 
> All warnings:
> 
>    sound/pci/asihpi/hpioctl.c: In function 'asihpi_hpi_ioctl':
>>> sound/pci/asihpi/hpioctl.c:125:6: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
>>> sound/pci/asihpi/hpioctl.c:126:6: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
> --
>    net/atm/resources.c: In function 'atm_dev_ioctl':
>>> net/atm/resources.c:223:8: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
>>> net/atm/resources.c:274:7: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
> --

[... and so on ...]

Now I remember this problem.  I believe I discussed it with rmk in the
context of ARM, too.  Russell, did we ever find any way to implement
8-byte get_user() on 32 bits without massive warning spewage?

	-hpa

Re: sound/pci/asihpi/hpioctl.c:125:6: warning: cast to pointer from integer of different size

[Russell King - ARM Linux]

On Thu, Feb 07, 2013 at 06:19:35PM -0800, H. Peter Anvin wrote:
> On 02/07/2013 03:45 PM, kbuild test robot wrote:
> > tree:   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/mm
> > head:   6fcddf474ae1c8e2fb5f14c850c8aa018e7a5034
> > commit: 6fcddf474ae1c8e2fb5f14c850c8aa018e7a5034 x86-32: Add support for 64bit get_user()
> > date:   2 hours ago
> > config: make ARCH=i386 allmodconfig
> >
> > All warnings:
> >
> >    sound/pci/asihpi/hpioctl.c: In function 'asihpi_hpi_ioctl':
> >>> sound/pci/asihpi/hpioctl.c:125:6: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
> >>> sound/pci/asihpi/hpioctl.c:126:6: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
> > --
> >    net/atm/resources.c: In function 'atm_dev_ioctl':
> >>> net/atm/resources.c:223:8: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
> >>> net/atm/resources.c:274:7: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
> > --
>
> [... and so on ...]
>
> Now I remember this problem.  I believe I discussed it with rmk in the
> context of ARM, too.  Russell, did we ever find any way to implement
> 8-byte get_user() on 32 bits without massive warning spewage?

My last attempt for ARM that I can find (though it wasn't my last email)
was:

#define __get_user_x(__r2,__p,__e,__s,__i...)				\
	   __asm__ __volatile__ (					\
		"bl	__get_user_" #__s				\
		: "=&r" (__e), "=r" (__r2)				\
		: "0" (__p)						\
		: __i, "cc")

#ifdef BIG_ENDIAN
#define __get_user_xb(__r2,__p,__e,__s,__i...)				\
	__get_user_x(__r2,(uintptr_t)__p + 4,__s,__i)
#else
#define __get_user_xb __get_user_x
#endif

#define get_user(x,p)							\
	({								\
		register const typeof(*(p)) __user *__p asm("r0") = (p);\
		register int __e asm("r0");				\
		register typeof(x) __r2 asm("r2");			\
		switch (sizeof(*(__p))) {				\
		case 1: 						\
			__get_user_x(__r2, __p, __e, 1, "lr");		\
			break;						\
		case 2: 						\
			__get_user_x(__r2, __p, __e, 2, "r3", "lr");	\
			break;						\
		case 4: 						\
			__get_user_x(__r2, __p, __e, 4, "lr");		\
			break;						\
		case 8: 						\
			if (sizeof((x)) < 8)				\
				__get_user_xb(__r2, __p, __e, 4, "lr"); \
			else						\
				__get_user_x(__r2, __p, __e, 8, "lr");	\
			break;						\
		default: __e = __get_user_bad(); break; 		\
		}							\
		x = (typeof(*(__p))) __r2;				\
		__e;							\
	})

which I claimed did work for ARM, but I doubted it'd work everywhere
because it relies upon there being no 8-bit or 16-bit "registers" being
available - iow, it replies upon a register for byte and half-word
variables being a full register where the value gets sign-extended to
the full register.

This is important because of the "typeof(x) __r2 asm("r2")" which may
end up being a char, short or int-sized, but __get_user_x() effectively
writing to the whole word.

Consider the case where 'x' and '*p' are two different sizes.

Whether that's safe for x86 or not, I don't know, but my suspicions are
that it's unsafe on x86 as it's possible to refer to the various bytes/
half-words of eax separately.

So, I came to the conclusion that if x86 remains a problem, there's
little point supporting it on ARM.

Re: sound/pci/asihpi/hpioctl.c:125:6: warning: cast to pointer from integer of different size

[H. Peter Anvin]

On 02/08/2013 07:28 AM, Russell King - ARM Linux wrote:
> 
> Whether that's safe for x86 or not, I don't know, but my suspicions are
> that it's unsafe on x86 as it's possible to refer to the various bytes/
> half-words of eax separately.
> 
> So, I came to the conclusion that if x86 remains a problem, there's
> little point supporting it on ARM.
> 

It is possible to access bytes separately, but gcc generally doesn't.
However, whether or not that can be relied upon safely is a tricky question.

It *is* also worth nothing that the x86 ABI does allow two words to be
returned in registers from a normal C function, simply by returning a
structure.  That doesn't solve the problem at hand, though, which is how
to make a type-neutral macro which can handle doublewords...

	-hpa

Re: sound/pci/asihpi/hpioctl.c:125:6: warning: cast to pointer from integer of different size

[Ville Syrjälä]

[-- Attachment #1: Type: text/plain, Size: 1519 bytes --]

On Fri, Feb 08, 2013 at 09:06:52AM -0800, H. Peter Anvin wrote:
> On 02/08/2013 07:28 AM, Russell King - ARM Linux wrote:
> > 
> > Whether that's safe for x86 or not, I don't know, but my suspicions are
> > that it's unsafe on x86 as it's possible to refer to the various bytes/
> > half-words of eax separately.
> > 
> > So, I came to the conclusion that if x86 remains a problem, there's
> > little point supporting it on ARM.
> > 
> 
> It is possible to access bytes separately, but gcc generally doesn't.
> However, whether or not that can be relied upon safely is a tricky question.
> 
> It *is* also worth nothing that the x86 ABI does allow two words to be
> returned in registers from a normal C function, simply by returning a
> structure.  That doesn't solve the problem at hand, though, which is how
> to make a type-neutral macro which can handle doublewords...

I just tried to compare a couple of options:

1)
	unsigned long __val_gu;
	unsigned long long __val_gu8;

2)
	register typeof(x) __val_gu asm("eax");

	I was still using a test app based on my orignal patch which
	used eax and edx for the value.

3)
	typeof(x) __val_gu;

While options 2 and 3 get rid of the warnings, they unfortunately
produce different results as well.

I've attached my test app in case you want to see it.

One other note is that if I include the memtest() call in the test,
option 1 and 2 produce the same results, but w/o the memtest() the
results differ. I didn't look into it any further.

-- 
Ville Syrjälä
Intel OTC

[-- Attachment #2: get_user.S --]
[-- Type: text/x-asm, Size: 701 bytes --]

#ifdef AMD64
#define _ASM_AX rax
#define _ASM_CX rcx
#define _ASM_DX rdx
#else
#define _ASM_AX eax
#define _ASM_CX ecx
#define _ASM_DX edx
#endif

.text
.globl __get_user_1
.globl __get_user_2
.globl __get_user_4
#ifdef AMD64
.globl __get_user_8
#else
.globl __get_user_8_32
#endif

__get_user_1:
	movzb (%_ASM_CX),%eax
	xor %ecx,%ecx
	ret

__get_user_2:
	add $1,%_ASM_CX
	movzwl -1(%_ASM_CX),%eax
	xor %ecx,%ecx
	ret

__get_user_4:
	add $3,%_ASM_CX
	mov -3(%_ASM_CX),%eax
	xor %ecx,%ecx
	ret

#ifdef AMD64
__get_user_8:
	add $7,%_ASM_CX
	movq -7(%_ASM_CX),%_ASM_AX
	xor %ecx,%ecx
	ret
#else
__get_user_8_32:
	add $7,%_ASM_CX
	movl -7(%_ASM_CX),%eax
	movl -3(%_ASM_CX),%edx
	xor %ecx,%ecx
	ret
#endif

[-- Attachment #3: Makefile --]
[-- Type: text/plain, Size: 204 bytes --]

CFLAGS:=-std=gnu99 -O2

CPPFLAGS:=-DAMD64
#CFLAGS+=-m32
#ASFLAGS+=-m32

CPPFLAGS+=-Wint-to-pointer-cast

.PHONY: all clean

all: test

test: uaccess.o get_user.o
	$(CC) $(CFLAGS) -o $@ $^

clean:
	rm *.o

[-- Attachment #4: uaccess.c --]
[-- Type: text/x-c, Size: 3710 bytes --]

#include <stdio.h>
#include <stdint.h>
#include <inttypes.h>
#include <string.h>

#define OPT 1

#define __get_user_x(size, ret, x, ptr)				      \
	asm volatile("call __get_user_" #size			      \
		     : "=c" (ret), "=a" (x)			      \
		     : "0" (ptr))


#ifdef AMD64
#define __get_user_8(__ret_gu, __val_gu, ptr)                           \
	__get_user_x(8, __ret_gu, __val_gu, ptr)
#else
#define __get_user_8(ret, x, ptr)					\
	asm volatile("call __get_user_8_32"				\
		     : "=c" (ret), "=A" (x)				\
		     : "0" (ptr))
#endif

#if OPT == 1
#define get_user(x, ptr)						\
({									\
	int __ret_gu;							\
	unsigned long __val_gu;						\
	unsigned long long __val_gu8;					\
	switch (sizeof(*(ptr))) {					\
	case 1:                                                         \
		__get_user_x(1, __ret_gu, __val_gu, ptr);		\
		break;							\
	case 2:								\
		__get_user_x(2, __ret_gu, __val_gu, ptr);		\
		break;							\
	case 4:								\
		__get_user_x(4, __ret_gu, __val_gu, ptr);		\
		break;							\
	case 8:								\
		__get_user_8(__ret_gu, __val_gu8, ptr);			\
		break;							\
	default:							\
		__get_user_x(X, __ret_gu, __val_gu, ptr);		\
		break;							\
	}								\
	if (sizeof(*(ptr)) == 8)					\
		(x) = (typeof(*(ptr)))__val_gu8;			\
	else								\
		(x) = (typeof(*(ptr)))__val_gu;				\
	__ret_gu;							\
})
#endif

#if OPT == 2
#define get_user(x, ptr)						\
({									\
	int __ret_gu;							\
	register typeof(x) __val_gu asm("eax");				\
	switch (sizeof(*(ptr))) {					\
	case 1:                                                         \
		__get_user_x(1, __ret_gu, __val_gu, ptr);		\
		break;							\
	case 2:								\
		__get_user_x(2, __ret_gu, __val_gu, ptr);		\
		break;							\
	case 4:								\
		__get_user_x(4, __ret_gu, __val_gu, ptr);		\
		break;							\
	case 8:								\
		__get_user_8(__ret_gu, __val_gu, ptr);			\
		break;							\
	default:							\
		__get_user_x(X, __ret_gu, __val_gu, ptr);		\
		break;							\
	}								\
	(x) = (typeof(*(ptr)))__val_gu;					\
	__ret_gu;							\
})
#endif

#if OPT == 3
#define get_user(x, ptr)						\
({									\
	int __ret_gu;							\
	typeof(x) __val_gu;						\
	switch (sizeof(*(ptr))) {					\
	case 1:                                                         \
		__get_user_x(1, __ret_gu, __val_gu, ptr);		\
		break;							\
	case 2:								\
		__get_user_x(2, __ret_gu, __val_gu, ptr);		\
		break;							\
	case 4:								\
		__get_user_x(4, __ret_gu, __val_gu, ptr);		\
		break;							\
	case 8:								\
		__get_user_8(__ret_gu, __val_gu, ptr);			\
		break;							\
	default:							\
		__get_user_x(X, __ret_gu, __val_gu, ptr);		\
		break;							\
	}								\
	(x) = (typeof(*(ptr)))__val_gu;					\
	__ret_gu;							\
})
#endif

int main(void)
{
	uint64_t foo = 0x89abcdef76543210;

	printf(" foo: %"PRIx64"\n", foo);

	struct {
		uint8_t sika1;
		uint16_t sika2;
		uint32_t sika4;
		uint64_t sika8;
	} __attribute__((__packed__)) x;

	if (get_user(x.sika8, (const uint64_t*)&foo)) return 1;
	if (get_user(x.sika4, (const uint64_t*)&foo)) return 1;
	if (get_user(x.sika2, (const uint64_t*)&foo)) return 1;
	if (get_user(x.sika1, (const uint64_t*)&foo)) return 1;
	printf("sika8: %"PRIx64"\n", x.sika8);
	printf("sika4: %x\n", x.sika4);
	printf("sika2: %x\n", x.sika2);
	printf("sika1: %x\n", x.sika1);

	//memset(&x, 0, sizeof(x));

	if (get_user(x.sika1, (const uint64_t*)&foo)) return 1;
	if (get_user(x.sika2, (const uint64_t*)&foo)) return 1;
	if (get_user(x.sika4, (const uint64_t*)&foo)) return 1;
	if (get_user(x.sika8, (const uint64_t*)&foo)) return 1;
	printf("sika8: %"PRIx64"\n", x.sika8);
	printf("sika4: %x\n", x.sika4);
	printf("sika2: %x\n", x.sika2);
	printf("sika1: %x\n", x.sika1);

	return 0;
}

Re: sound/pci/asihpi/hpioctl.c:125:6: warning: cast to pointer from integer of different size

[Russell King - ARM Linux]

On Fri, Feb 08, 2013 at 08:50:57PM +0200, Ville Syrjälä wrote:
> 	struct {
> 		uint8_t sika1;
> 		uint16_t sika2;
> 		uint32_t sika4;
> 		uint64_t sika8;

Note - you also need to check what the behaviour is with a pointer type
too - that's the one that gets ARM if you try this.  My test set on ARM
was:

int test_8(unsigned char *v, unsigned char *p)
{
        return get_user(*v, p);
}

int test_16(unsigned short *v, unsigned short *p)
{
        return get_user(*v, p);
}

int test_32(unsigned int *v, unsigned int *p)
{
        return get_user(*v, p);
}

int test_32_constp(unsigned int *v, const unsigned int *p)
{
        return get_user(*v, p);
}

int test_64(unsigned long long *v, unsigned long long *p)
{
        return get_user(*v, p);
}

int test_64_narrow(unsigned long *v, unsigned long long *p)
{
        return get_user(*v, p);
}

int test_ptr(unsigned int **v, unsigned int **p)
{
        return get_user(*v, p);
}

int test_wrong(char **v, const char **p)
{
        return get_user(*v, p);
}

All but the last should build cleanly and correctly.  The last should
issue a warning.