Messages in this thread | | | Date | Fri, 8 Feb 2013 20:50:57 +0200 | From | Ville Syrjälä <> | Subject | Re: sound/pci/asihpi/hpioctl.c:125:6: warning: cast to pointer from integer of different size |
| |
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 #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 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 #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; }
| |