From: Christophe Leroy <christophe.leroy@c-s.fr>
To: Christoph Hellwig <hch@infradead.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] powerpc/irq: don't use current_stack_pointer() in do_IRQ()
Date: Thu, 12 Dec 2019 17:29:06 +0100 [thread overview]
Message-ID: <185df2a7-e6c4-0d2d-59cd-760df94fa3c6@c-s.fr> (raw)
In-Reply-To: <20191212125116.GA3381@infradead.org>
Le 12/12/2019 à 13:51, Christoph Hellwig a écrit :
> Why can't current_stack_pointer be turned into an inline function using
> inline assembly? That would reduce the overhead for all callers.
>
In the old days, it was a macro, and it was changed into an assembly
function by commit
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=bfe9a2cfe91a
It was later renamed from __get_SP() to current_stack_pointer() by
commit
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=acf620ecf56cfc4edaffaf158250e128539cdd26
But in fact this function is badly named as it doesn't provide the
current stack pointer but a pointer to the parent's stack frame.
Having it as an extern function forces GCC to set a stack frame in the
calling function. If inline assembly is used instead, there's a risk of
not getting a stack frame in the calling function, in which case the
current_stack_pointer() will return the grandparent's stackframe pointer
instead of the parent's one.
Christophe
prev parent reply other threads:[~2019-12-12 16:29 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-08 10:48 [PATCH] powerpc/irq: don't use current_stack_pointer() in do_IRQ() Christophe Leroy
2019-12-12 12:51 ` Christoph Hellwig
2019-12-12 16:29 ` Christophe Leroy [this message]
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