[PING][PATCH] ARM/Linux: Unwind restart_syscall(2) frames

Daniel Jacobowitz drow@false.org
Tue Dec 22 16:17:00 GMT 2009


On Tue, Dec 22, 2009 at 03:28:41PM +0000, Richard Earnshaw wrote:
> It's not code that I'm familiar with, however...
> 
> 	svc	0x00900000
> 	ldr	pc, [sp], #12
> then
> 
> +  trad_frame_set_reg_value (this_cache, ARM_SP_REGNUM, sp + 12);
> 
> So why is the stack pointer /incremented/ by 12 at this point (which
> deallocates stack) rather than decremented to compensate for the
> increment that will follow?  Also, shouldn't the stack allocation be a
> multiple of 8 to fully conform to the ABI stack alignment constraints?

We're before execution of the above trampoline at this point, trying
to compensate for it; that's why the stack goes up, we're simulating
return from the trampoline.  The code sequence was chosen by the
kernel, weird stack alignment and all.

-- 
Daniel Jacobowitz
CodeSourcery



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