http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46483
Summary: Built-in memcpy() does not handle unaligned int for
ARM
Product: gcc
Version: 4.5.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: fredrik.hederstie...@securitas-direct.com
I had some problems with memcpy() when copying unaligned integers for ARM.
For intel target it worked fine, and I concluded that if I overloaded gcclib
weak memcpy-reference I had the same problem, but if I just overloaded memcpy
with a #define to my own function, it worked fine.
At first glance I though it was just a possible strict-aliasing violation, but
when having a closer look I'm not so sure, so I submit this to Bugzilla anyway
for validation.
I submit some lines of source-code that gives an example of the problem.
----------------------
#include <stdio.h>
----------------------
struct unaligned_int {
char dummy1;
char dummy2;
char dummy3;
unsigned int number;
} __attribute__((packed));
//---------------------
void *my_memcpy(void *dst, const void *src, size_t n)
{
char *s = (char*)src;
char *d = (char*)dst;
while (n--) {
*d++ = *s++;
}
return dst;
}
//---------------------
static void copy_x_into_struct(char *buf, unsigned int x)
{
unsigned int i;
struct unaligned_int* testp = (struct unaligned_int*)buf;
memset(buf, 0xFF, sizeof(unsigned int));
memcpy((void*)&(testp->number), &x, sizeof(unsigned int));
printf("BUILT-IN MEMCPY TO %08x: ", &(testp->number));
for (i = 0; i < sizeof(struct unaligned_int); i++) {
printf(" %02x", buf[i]);
}
printf("\n");
memset(buf, 0xFF, sizeof(unsigned int));
my_memcpy((void*)&(testp->number), &x, sizeof(int));
printf("USER-DEF MEMCPY TO %08x: ", &(testp->number));
for (i = 0; i < sizeof(struct unaligned_int); i++) {
printf(" %02x", buf[i]);
}
printf("\n");
}
//---------------------
int main(void)
{
char buf[100];
unsigned int x = 0x12345678;
copy_x_into_struct(buf, x);
return 0;
}
-------------------------
PROGRAM OUTPUT:
BUILT-IN MEMCPY TO 04016bd7: 78 56 34 12 00 00 00
USER-DEF MEMCPY TO 04016bd7: ff ff ff 78 56 34 12
-------------------------
GCC-COMMAND-LINE:
arm-elf-gcc -g3 -ggdb3 -gdwarf-2 -mthumb -c -Wall -W -Wextra
-Wno-unused-parameter -mcpu=arm966e-s -Os -fno-omit-frame-pointer -fno-web
-mhard-float -mfpu=fpa -ffunction-sections -fdata-sections
-o test.o test.c
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TOOLCHAIN: Attaching toolchain build-script.
