When the immediate encoded in the instruction is accessed, it is sign
extended due to being a signed value being assigned to a signed integer.
The ISA specifies that this operation is an unsigned operation.
The sign extension leads us to incorrectly decode:

801e9c8e:       cbf1            sw      ra,68(sp)

As having an immediate of 1073741809.

Since the instruction format does not specify signed/unsigned, and this
is currently the only location to use this instuction format, change it
to an unsigned immediate.

Fixes: bb9bc4689b9c ("MIPS: Calculate microMIPS ra properly when unwinding the 
stack")
Suggested-by: Paul Burton <paul.bur...@imgtec.com>
Signed-off-by: Matt Redfearn <matt.redfe...@imgtec.com>
Reviewed-by: James Hogan <james.ho...@imgtec.com>

---

Changes in v3: None
Changes in v2: None

 arch/mips/include/uapi/asm/inst.h | 2 +-
 arch/mips/kernel/process.c        | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/mips/include/uapi/asm/inst.h 
b/arch/mips/include/uapi/asm/inst.h
index d61897535926..6abea5183d7c 100644
--- a/arch/mips/include/uapi/asm/inst.h
+++ b/arch/mips/include/uapi/asm/inst.h
@@ -981,7 +981,7 @@ struct mm16_r3_format {             /* Load from global 
pointer format */
 struct mm16_r5_format {                /* Load/store from stack pointer format 
*/
        __BITFIELD_FIELD(unsigned int opcode : 6,
        __BITFIELD_FIELD(unsigned int rt : 5,
-       __BITFIELD_FIELD(signed int simmediate : 5,
+       __BITFIELD_FIELD(unsigned int imm : 5,
        __BITFIELD_FIELD(unsigned int : 16, /* Ignored */
        ;))))
 };
diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index 288a79bd0e72..6fa726b0be01 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -214,7 +214,7 @@ static inline int is_ra_save_ins(union mips_instruction 
*ip, int *poff)
                        if (ip->mm16_r5_format.rt != 31)
                                return 0;
 
-                       *poff = ip->mm16_r5_format.simmediate;
+                       *poff = ip->mm16_r5_format.imm;
                        *poff = (*poff << 2) / sizeof(ulong);
                        return 1;
 
-- 
2.7.4

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