linux-kernel - Re: [PATCH 1/3] powerpc/uaccess: Switch __put_user_size_allowed() to __put_user_asm

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Date:   Wed, 28 Oct 2020 00:26:16 +0100
From:   Andreas Schwab <schwab@...ux-m68k.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] powerpc/uaccess: Switch __put_user_size_allowed()
 to __put_user_asm_goto()

On Sep 04 2020, Christophe Leroy wrote:

> __put_user_asm_goto() provides more flexibility to GCC and avoids using
> a local variable to tell if the write succeeded or not.
> GCC can then avoid implementing a cmp in the fast path.

That breaks CLONE_CHILD_SETTID.  I'm getting an assertion failure in
__libc_fork (THREAD_GETMEM (self, tid) != ppid).

Andreas.

-- 
Andreas Schwab, schwab@...ux-m68k.org
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