ftrace/x86: Set ftrace_stub to weak to prevent gcc from using short jumps to it

2017-07-04T09:51:17+00:00

commit 8329e818f14926a6040df86b2668568bde342ebf upstream. 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: http://lkml.kernel.org/r/20160516230035.1dbae571@gandalf.local.home Reported-by: Matt Fleming Reported-by: Namhyung Kim Tested-by: Matt Fleming Reviewed-by: Masami Hiramatsu Signed-off-by: Steven Rostedt Signed-off-by: Willy Tarreau

3.10.71 -> 3.10.72

2016-08-26T13:59:49+00:00

first commit

2016-08-15T02:19:42+00:00

xavi/android_kernel_m2note/arch/x86/kernel/entry_64.S, branch ng-7.1.2

ftrace/x86: Set ftrace_stub to weak to prevent gcc from using short jumps to it

3.10.71 -> 3.10.72

first commit