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Re: [PATCH 08/19] nptl: arm: Fix Race conditions in pthread cancellation (BZ#12683)

On Mon, 11 Dec 2017, Adhemerval Zanella wrote:

> +ENTRY (__syscall_cancel_arch)
> +	.fnstart
> +	mov	ip,sp
> +	stmfd	sp!, {r4,r5,r6,r7,lr}
> +	.save	{r4,r5,r6,r7,lr}
> +
> +	cfi_adjust_cfa_offset (20)
> +	cfi_rel_offset (lr, 16)

I'd expect the saves of other registers to be described in the CFI as well 
(that is, the .debug_frame CFI which is generated by cfi_* on ARM).

> +	.globl __syscall_cancel_arch_end
> +__syscall_cancel_arch_end:
> +	ldmfd	sp!, {r4,r5,r6,r7,lr}
> +	cfi_adjust_cfa_offset (-20);

Then, I'd expect cfi_restore calls here.

> +1:
> +	mov	lr, pc
> +	b	__syscall_do_cancel

And this code is jumped to from a position where the stack has been 
adjusted, but the CFI at this point reflects a state where it has been 
restored.  So you need a fresh set of CFI directives to make the CFI 
accurate in this part of the function.  (I haven't checked whether any 
other architecture versions of this function might have similar CFI 

Also, it looks like you jump to the C function __syscall_do_cancel with a 
stack adjustment that is not a multiple of 8.  I think the AAPCS 
requirement for the stack pointer to be a multiple of 8 at public 
interfaces applies to such a jump to a C function, so you need to save and 
restore an additional register to preserve alignment.

Joseph S. Myers

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