This is a note to let you know that I've just added the patch titled ftrace/x86_32: Set ftrace_stub to weak to prevent gcc from using short jumps to it to the 4.8-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: ftrace-x86_32-set-ftrace_stub-to-weak-to-prevent-gcc-from-using-short-jumps-to-it.patch and it can be found in the queue-4.8 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 847fa1a6d3d00f3bdf68ef5fa4a786f644a0dd67 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx> Date: Thu, 8 Dec 2016 12:48:26 -0500 Subject: ftrace/x86_32: Set ftrace_stub to weak to prevent gcc from using short jumps to it From: Steven Rostedt (Red Hat) <rostedt@xxxxxxxxxxx> 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@xxxxxxxxxxxxx> Tested-by: Colin Ian King <colin.king@xxxxxxxxxxxxx> Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/entry/entry_32.S | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -852,8 +852,8 @@ 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) Patches currently in stable-queue which might be from rostedt@xxxxxxxxxxx are queue-4.8/ftrace-x86_32-set-ftrace_stub-to-weak-to-prevent-gcc-from-using-short-jumps-to-it.patch queue-4.8/fgraph-handle-a-case-where-a-tracer-ignores-set_graph_notrace.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html