mips: ftrace: fix static function graph tracing

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@universe-factory.net>
Tested-by: Matt Redfearn <matt.redfearn@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/18929/
Signed-off-by: Paul Burton <paul.burton@mips.com>
Cc: stable@vger.kernel.org # v3.17+

diff --git a/arch/mips/kernel/mcount.S b/arch/mips/kernel/mcount.S
index f2ee7e1e3342e498be961f8995fc91b1de1f2744..cff52b283e03843519201ca8fe8754e0899c0c3c 100644 (file)
--- 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