Messages in this thread Patch in this message | | | From | Willy Tarreau <> | Subject | [PATCH 3.10 034/250] ftrace/x86_32: Set ftrace_stub to weak to prevent gcc from using short jumps to it | Date | Thu, 8 Jun 2017 00:57:00 +0200 |
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From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>
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 <colin.king@canonical.com> Tested-by: Colin Ian King <colin.king@canonical.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Willy Tarreau <w@1wt.eu> --- arch/x86/kernel/entry_32.S | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S index 5c38e2b..c502340 100644 --- a/arch/x86/kernel/entry_32.S +++ b/arch/x86/kernel/entry_32.S @@ -1103,8 +1103,8 @@ 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) -- 2.8.0.rc2.1.gbe9624a
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