| From 847fa1a6d3d00f3bdf68ef5fa4a786f644a0dd67 Mon Sep 17 00:00:00 2001 |
| From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org> |
| 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@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: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| 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) |
| |
