[PATCH 3.16 006/212] MIPS: Clear ISA bit correctly in get_frame_info()

[Ben Hutchings]

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

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

From: Paul Burton <paul.burton@xxxxxxxxxx>

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 <paul.burton@xxxxxxxxxx>
Fixes: 34c2f668d0f6 ("MIPS: microMIPS: Add unaligned access support.")
Cc: Leonid Yegoshin <leonid.yegoshin@xxxxxxxxxx>
Cc: linux-mips@xxxxxxxxxxxxxx
Patchwork: https://patchwork.linux-mips.org/patch/14528/
Signed-off-by: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/mips/kernel/process.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -331,17 +331,14 @@ static inline int is_sp_move_ins(union m
 
 static int get_frame_info(struct mips_frame_info *info)
 {
-#ifdef CONFIG_CPU_MICROMIPS
-	union mips_instruction *ip = (void *) (((char *) info->func) - 1);
-#else
-	union mips_instruction *ip = info->func;
-#endif
+	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;