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

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

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

From: Paul Burton <paul.burton@imgtec.com>

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@imgtec.com>
Fixes: 34c2f668d0f6 ("MIPS: microMIPS: Add unaligned access support.")
Cc: Leonid Yegoshin <leonid.yegoshin@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14528/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 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;
 

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[PATCH 3.16 000/212] 3.16.44-rc1 review Ben Hutchings <ben@decadent.org.uk> - 2017-06-01 18:50 +0200
  [PATCH 3.16 003/212] adm80211: return an error if adm8211_alloc_rings()  fails Ben Hutchings <ben@decadent.org.uk> - 2017-06-01 18:50 +0200
  [PATCH 3.16 006/212] MIPS: Clear ISA bit correctly in  get_frame_info() Ben Hutchings <ben@decadent.org.uk> - 2017-06-01 18:50 +0200
  [PATCH 3.16 023/212] Drivers: hv: vmbus: Raise retry/wait limits  in vmbus_post_msg() Ben Hutchings <ben@decadent.org.uk> - 2017-06-01 18:50 +0200
  [PATCH 3.16 008/212] MIPS: Fix get_frame_info() handling of  microMIPS function size Ben Hutchings <ben@decadent.org.uk> - 2017-06-01 18:50 +0200
  [PATCH 3.16 011/212] MIPS: Handle microMIPS jumps in the same way  as MIPS32/MIPS64 jumps Ben Hutchings <ben@decadent.org.uk> - 2017-06-01 18:50 +0200
  [PATCH 3.16 031/212] ASoC: rt5640: use msleep() for long delays Ben Hutchings <ben@decadent.org.uk> - 2017-06-01 18:50 +0200
  [PATCH 3.16 027/212] ext4: avoid deadlock when expanding inode size Ben Hutchings <ben@decadent.org.uk> - 2017-06-01 18:50 +0200
  [PATCH 3.16 004/212] iio: st_pressure: Fix data sign Ben Hutchings <ben@decadent.org.uk> - 2017-06-01 18:50 +0200
  [PATCH 3.16 001/212] mm/huge_memory.c: fix up "mm/huge_memory.c:  respect FOLL_FORCE/FOLL_COW for thp" backport Ben Hutchings <ben@decadent.org.uk> - 2017-06-01 18:50 +0200
  Re: [PATCH 3.16 000/212] 3.16.44-rc1 review Guenter Roeck <linux@roeck-us.net> - 2017-06-01 23:20 +0200

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