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[patch added to 3.12-stable] MIPS: Clear ISA bit correctly in get_frame_

Subject: [patch added to 3.12-stable] MIPS: Clear ISA bit correctly in get_frame_info()
From: Jiri Slaby <>
Date: Mon, 13 Mar 2017 20:51:16 +0100
Cc: Paul Burton <>, Leonid Yegoshin <>,, Ralf Baechle <>, Jiri Slaby <>
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From: Paul Burton <>

This patch has been added to the 3.12 stable tree. If you have any
objections, please let us know.


commit ccaf7caf2c73c6db920772bf08bf1d47b2170634 upstream.

get_frame_info() can be called in microMIPS kernels with the ISA bit
already clear. For example this happens when unwind_stack_by_address()
is called because we begin with a PC that has the ISA bit set & subtract
the (odd) offset from the preceding symbol (which does not have the ISA
bit set). Since get_frame_info() unconditionally subtracts 1 from the PC
in microMIPS kernels it incorrectly misaligns the address it then
attempts to access code at, leading to an address error exception.

Fix this by using msk_isa16_mode() to clear the ISA bit, which allows
get_frame_info() to function regardless of whether it is provided with a
PC that has the ISA bit set or not.

Signed-off-by: Paul Burton <>
Fixes: 34c2f668d0f6 ("MIPS: microMIPS: Add unaligned access support.")
Cc: Leonid Yegoshin <>
Signed-off-by: Ralf Baechle <>
Signed-off-by: Jiri Slaby <>
 arch/mips/kernel/process.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index ddc76103e78c..c5880a894a25 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -325,17 +325,14 @@ static inline int is_sp_move_ins(union mips_instruction 
 static int get_frame_info(struct mips_frame_info *info)
-       union mips_instruction *ip = (void *) (((char *) info->func) - 1);
-       union mips_instruction *ip = info->func;
+       union mips_instruction *ip;
        unsigned max_insns = info->func_size / sizeof(union mips_instruction);
        unsigned i;
        info->pc_offset = -1;
        info->frame_size = 0;
+       ip = (void *)msk_isa16_mode((ulong)info->func);
        if (!ip)
                goto err;

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