[PATCH 3.2 071/102] MIPS: mcount: Adjust stack pointer for static trace in MIPS32

[Ben Hutchings]

3.2.64-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Markos Chandras <markos.chandras@xxxxxxxxxx>

commit 8a574cfa2652545eb95595d38ac2a0bb501af0ae upstream.

Every mcount() call in the MIPS 32-bit kernel is done as follows:

[...]
move at, ra
jal _mcount
addiu sp, sp, -8
[...]

but upon returning from the mcount() function, the stack pointer
is not adjusted properly. This is explained in details in 58b69401c797
(MIPS: Function tracer: Fix broken function tracing).

Commit ad8c396936e3 ("MIPS: Unbreak function tracer for 64-bit kernel.)
fixed the stack manipulation for 64-bit but it didn't fix it completely
for MIPS32.

Signed-off-by: Markos Chandras <markos.chandras@xxxxxxxxxx>
Cc: linux-mips@xxxxxxxxxxxxxx
Patchwork: https://patchwork.linux-mips.org/patch/7792/
Signed-off-by: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/mips/kernel/mcount.S | 12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/arch/mips/kernel/mcount.S
+++ b/arch/mips/kernel/mcount.S
@@ -119,7 +119,11 @@ NESTED(_mcount, PT_SIZE, ra)
 	 nop
 #endif
 	b	ftrace_stub
+#ifdef CONFIG_32BIT
+	 addiu sp, sp, 8
+#else
 	 nop
+#endif
 
 static_trace:
 	MCOUNT_SAVE_REGS
@@ -129,6 +133,9 @@ static_trace:
 	 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
@@ -177,6 +184,11 @@ NESTED(ftrace_graph_caller, PT_SIZE, ra)
 	jal	prepare_ftrace_return
 	 nop
 	MCOUNT_RESTORE_REGS
+#ifndef CONFIG_DYNAMIC_FTRACE
+#ifdef CONFIG_32BIT
+	addiu sp, sp, 8
+#endif
+#endif
 	RETURN_BACK
 	END(ftrace_graph_caller)
 

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