Re: [PATCH] MIPS: lib: Mark intrinsics notrace

From: Harvey Hunt
Date: Tue May 31 2016 - 08:18:38 EST

Hi Ralf,

On 29/05/16 22:03, Ralf Baechle wrote:
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.

This is triggered by building with CONFIG_CC_OPTIMIZE_FOR_SIZE. This explains why I only saw it on certain MIPS32 devices - Malta's defconfigs don't have CONFIG_CC_OPTIMIZE_FOR_SIZE enabled, but the pistachio and Ci20 defconfigs do.