path: root/tools
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authorSteven Rostedt <>2016-05-16 23:00:35 -0400
committerSteven Rostedt <>2016-05-20 13:28:40 -0400
commit8329e818f14926a6040df86b2668568bde342ebf (patch)
tree98621bc3f846b96661bccc4c57c8672bde21e95c /tools
parent6112a300c9e41993cc0dc56ac393743d28381284 (diff)
ftrace/x86: Set ftrace_stub to weak to prevent gcc from using short jumps to it
Matt Fleming reported seeing crashes when enabling and disabling function profiling which uses function graph tracer. Later Namhyung Kim hit a similar issue and he found that the issue was due to the jmp to ftrace_stub in ftrace_graph_call was only two bytes, and when it was changed to jump to the tracing code, it overwrote the ftrace_stub that was after it. Masami Hiramatsu bisected this down to a binutils change: 8dcea93252a9ea7dff57e85220a719e2a5e8ab41 is the first bad commit commit 8dcea93252a9ea7dff57e85220a719e2a5e8ab41 Author: H.J. Lu <> Date: Fri May 15 03:17:31 2015 -0700 Add -mshared option to x86 ELF assembler This patch adds -mshared option to x86 ELF assembler. By default, assembler will optimize out non-PLT relocations against defined non-weak global branch targets with default visibility. The -mshared option tells the assembler to generate code which may go into a shared library where all non-weak global branch targets with default visibility can be preempted. The resulting code is slightly bigger. This option only affects the handling of branch instructions. Declaring ftrace_stub as a weak call prevents gas from using two byte jumps to it, which would be converted to a jump to the function graph code. Link: Reported-by: Matt Fleming <> Reported-by: Namhyung Kim <> Tested-by: Matt Fleming <> Reviewed-by: Masami Hiramatsu <> Signed-off-by: Steven Rostedt <>
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