From: Steven Rostedt (Red Hat) Date: Thu, 8 Dec 2016 17:48:26 +0000 (-0500) Subject: ftrace/x86_32: Set ftrace_stub to weak to prevent gcc from using short jumps to it X-Git-Tag: firefly_0821_release~176^2~4^2~6^2~18 X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=2ef502e860f12b9e305151eef3bbb9ea4009a60d;p=firefly-linux-kernel-4.4.55.git ftrace/x86_32: Set ftrace_stub to weak to prevent gcc from using short jumps to it commit 847fa1a6d3d00f3bdf68ef5fa4a786f644a0dd67 upstream. With new binutils, gcc may get smart with its optimization and change a jmp from a 5 byte jump to a 2 byte one even though it was jumping to a global function. But that global function existed within a 2 byte radius, and gcc was able to optimize it. Unfortunately, that jump was also being modified when function graph tracing begins. Since ftrace expected that jump to be 5 bytes, but it was only two, it overwrote code after the jump, causing a crash. This was fixed for x86_64 with commit 8329e818f149, with the same subject as this commit, but nothing was done for x86_32. Fixes: d61f82d06672 ("ftrace: use dynamic patching for updating mcount calls") Reported-by: Colin Ian King Tested-by: Colin Ian King Signed-off-by: Steven Rostedt Signed-off-by: Greg Kroah-Hartman --- diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index f3b6d54e0042..ae678ad128a9 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -766,8 +766,8 @@ ftrace_graph_call: jmp ftrace_stub #endif -.globl ftrace_stub -ftrace_stub: +/* This is weak to keep gas from relaxing the jumps */ +WEAK(ftrace_stub) ret END(ftrace_caller)