ftrace_graph_caller was never run after calling ftrace_trace_function, breaking the function graph tracer. Fix this, bringing it in line with the x86 implementation. While we're at it, also streamline the control flow of _mcount a bit to reduce the number of branches. This issue was reported before: https://www.linux-mips.org/archives/linux-mips/2014-11/msg00295.html Signed-off-by: Matthias Schiffer <mschiffer@xxxxxxxxxxxxxxxxxxxx> --- Caveats: I've only tested this on 32bit; it would be great if someone with MIPS64 hardware or a working emulator setup could give it a spin. My test device runs on kernel 4.9.y, but I don't expect any problems applying the fix to newer kernels, given that this code is basically unchanged since 2014. I'm not sure what the correct Fixes: line would be. I did not bother to bisect the issue and could not find the commit introducing it by inspecting the log (assuming the tracer worked at some point). arch/mips/kernel/mcount.S | 27 ++++++++++++--------------- 1 file changed, 12 insertions(+), 15 deletions(-) diff --git a/arch/mips/kernel/mcount.S b/arch/mips/kernel/mcount.S index f2ee7e1e3342..cff52b283e03 100644 --- a/arch/mips/kernel/mcount.S +++ b/arch/mips/kernel/mcount.S @@ -119,10 +119,20 @@ NESTED(_mcount, PT_SIZE, ra) EXPORT_SYMBOL(_mcount) PTR_LA t1, ftrace_stub PTR_L t2, ftrace_trace_function /* Prepare t2 for (1) */ - bne t1, t2, static_trace + beq t1, t2, fgraph_trace nop + MCOUNT_SAVE_REGS + + move a0, ra /* arg1: self return address */ + jalr t2 /* (1) call *ftrace_trace_function */ + move a1, AT /* arg2: parent's return address */ + + MCOUNT_RESTORE_REGS + +fgraph_trace: #ifdef CONFIG_FUNCTION_GRAPH_TRACER + PTR_LA t1, ftrace_stub PTR_L t3, ftrace_graph_return bne t1, t3, ftrace_graph_caller nop @@ -131,24 +141,11 @@ EXPORT_SYMBOL(_mcount) bne t1, t3, ftrace_graph_caller nop #endif - b ftrace_stub -#ifdef CONFIG_32BIT - addiu sp, sp, 8 -#else - nop -#endif -static_trace: - MCOUNT_SAVE_REGS - - move a0, ra /* arg1: self return address */ - jalr t2 /* (1) call *ftrace_trace_function */ - move a1, AT /* arg2: parent's return address */ - - MCOUNT_RESTORE_REGS #ifdef CONFIG_32BIT addiu sp, sp, 8 #endif + .globl ftrace_stub ftrace_stub: RETURN_BACK -- 2.16.2
