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From: Florian Weimer <fw@deneb.enyo.de>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: "Carlos O'Donell" <carlos@redhat.com>,  GNU C Library <libc-alpha@sourceware.org>
Subject: Re: V2: [PATCH 02/24] x86: Support shadow stack pointer in setjmp/longjmp
References: <20180613153207.57232-1-hjl.tools@gmail.com>
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	<abc02573-7240-e248-9bfe-bdc324b9e07d@redhat.com>
	<20180713132252.GC2606@gmail.com> <87fu0lk2tf.fsf@mid.deneb.enyo.de>
	<CAMe9rOqufMcMEB0V0y8ssTYsOi2_31ad7W9rniRLHHvsGppUvQ@mail.gmail.com>
	<87wotxifg7.fsf@mid.deneb.enyo.de>
	<CAMe9rOpCHBK1bDmC6mVEB7rGhfEdp6Ka=juBNN3pzZsKnNSocg@mail.gmail.com>
	<87fu0kj50z.fsf@mid.deneb.enyo.de>
	<CAMe9rOqHrEzjWR3H7cYjM1X97WHSPy8m3TG97oxadhgRwiSm+w@mail.gmail.com>
Date: Sun, 15 Jul 2018 20:20:00 -0000
In-Reply-To: <CAMe9rOqHrEzjWR3H7cYjM1X97WHSPy8m3TG97oxadhgRwiSm+w@mail.gmail.com>
	(H. J. Lu's message of "Sun, 15 Jul 2018 06:54:30 -0700")
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* H. J. Lu:

>> #undef.  I think you can avoid that by using #if SHTSTK_ENABLED
>> instead of #ifdef SHADOW_STACK_POINTER_OFFSET, which also expresses
>> the intent more accurately.
>
> It is done on purpose.  sysdeps/x86_64/__longjmp.S has
>
> /* Don't restore shadow stack register if
>    1. Shadow stack isn't enabled.  Or
>    2. __longjmp is defined for __longjmp_cancel.
>  */
> #if !SHSTK_ENABLED || defined __longjmp
> # undef SHADOW_STACK_POINTER_OFFSET
> #endif

It's a bit awkward.

> Subject: [PATCH] x86_64: Undef SHADOW_STACK_POINTER_OFFSET last
>
> Since SHADOW_STACK_POINTER_OFFSET is defined in jmp_buf-ssp.h, we must
> undef SHADOW_STACK_POINTER_OFFSET after including <jmp_buf-ssp.h>.
>
> * sysdeps/unix/sysv/linux/x86_64/____longjmp_chk.S: Undef
> SHADOW_STACK_POINTER_OFFSET after including <jmp_buf-ssp.h>.

This looks okay as a fix.