Subramanyam Badri wrote:
Hi,
I am using a GCC compiler for ARM and see an alignment problem with pointer typecasting. We're porting code to ARM and found some writes to incorrect addresses. Can you help? For example:
char * pChar = (char *)0x100000; /* hardcoded for example purposes */
pChar[0] = 0x0;
*(int *)&pChar[1] = 0x11223344;
/* We really want pChar[0] to equal 0x00, but it equals 0x44 on ARM!!!! */
printf ("pChar[0] = 0x%02x\n", pChar[0]);
My understanding is that non-aligned memory access is allowed on ARM, so it's not clear why typecasting and writing data adjusts the destination address.
Your understanding isn't the same as mine - I would expect the cpu to
either trap on the unaligned access, or possibly just ignore the
misalignment.
If you're *lucky* enough to be running under linux, you can echo 3 to
/proc/cpu/alignment to enable the alignment fault handler. IIRC, its
default is to do the wrong thing, leaving partial memory updates like
you are seeing.
John
