Parallella Community

Hi,

I got some undesired behaviour with the compiler's generated code. It's said in the manual that structures and double words should be aligned to 8 bytes. I am makinh sure that the start if the stack is aligned to 8 bytes. Given that, some structures created within a function are not aligned to double-words, and subsequent read/write (which uses strd and ldrd instructions) accesses causes an exception to occur and hence the program hangs. Is there a compiler flag to force such a problem? Most of the flags like -malign-double -m64 are machine dependent (x86, sparc).

Regards,
Hesham

Digging into more details, the exact assembly store instruction that hangs the program is

ldrd r0,[fp,+0xc]
strd r0,[sp,+0xa] ;; here where it hangs

sp = 0x8effff04
fp = 0x8effff04
r0 = 0x0

Why fp is not aligned to 8 bytes? Given that the initial stack and fp address is "0x8EFFFF00" set at the linker script.
Some structures are not double-aligned when generated too, where I have to add __attribute__ ((align(8)));

Shouldn't the linker script setting up an 8-byte aligned stack to start with? The ABI requires that the stack is always 8-byte aligned so the compiler doesn't have to ever waste code aligning it.

You should provide an example and the flags you use.