linux-kernel - Re: [PATCH] MIPS: lib: Mark intrinsics notrace

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Message-ID: <20160529210340.GA25587@linux-mips.org>
Date:	Sun, 29 May 2016 23:03:41 +0200
From:	Ralf Baechle <ralf@...ux-mips.org>
To:	Harvey Hunt <harvey.hunt@...tec.com>
Cc:	linux-mips@...ux-mips.org, linux-kernel@...r.kernel.org,
	"# 4 . 2 . x-" <stable@...r.kernel.org>
Subject: Re: [PATCH] MIPS: lib: Mark intrinsics notrace

On Wed, May 25, 2016 at 11:06:35AM +0100, Harvey Hunt wrote:

> On certain MIPS32 devices, the ftrace tracer "function_graph" uses
> __lshrdi3() during the capturing of trace data. ftrace then attempts to
> trace __lshrdi3() which leads to infinite recursion and a stack overflow.
> Fix this by marking __lshrdi3() as notrace. Mark the other compiler
> intrinsics as notrace in case the compiler decides to use them in the
> ftrace path.

Makes perfect sense - but I'm wondering how you triggered it.  Was this
a build with the GCC option -Os that is CONFIG_CC_OPTIMIZE_FOR_SIZE?
Usually people build with CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE that is -O2
which results in intrinsics being inlined.

  Ralf