From: Corey Minyard <>

Modify the SAVE_SOME macro to look more like a standard
function, doing the arithmetic for the frame on the SP
register instead of copying it from K1, and by saving
the stored EPC from the RA.  This lets the get_frame_info()
function process this function like any other.  It also
remove an instruction or two from the kernel entry,
making it more efficient.

unwind_stack_by_address() has special handling for
the top of the interrupt stack, but without this change
unwinding will still fail if you get an interrupt while
handling an interrupt and try to do a traceback from
the second interrupt.

This change modifies the get_saved_sp macro to
optionally store the fetched value right into sp and store the
old SP value into K0.  Then it's just a matter of subtracting
the frame from SP and storing the old SP from K0.

This required changing the DADDI workaround a bit, since K0
holds the SP, we had to use K1 for AT.  But it eliminated
some of the special handling for the DADDI workaround.

Saving the RA register was moved up to before fetching the
CP0_EPC register, so the CP0_EPC register could be stored
into RA and the saved.  This lets the traceback code know
where RA is actually stored.

Signed-off-by: Corey Minyard <>
 arch/mips/include/asm/stackframe.h | 51 +++++++++++++++++++++++++++-----------
 1 file changed, 37 insertions(+), 14 deletions(-)

diff --git a/arch/mips/include/asm/stackframe.h 
index eaa5a4d..d2fb919 100644
--- a/arch/mips/include/asm/stackframe.h
+++ b/arch/mips/include/asm/stackframe.h
@@ -83,8 +83,16 @@
                LONG_S  $30, PT_R30(sp)
+ * get_saved_sp returns the SP for the current CPU by looking in the
+ * kernelsp array for it.  If tosp is set, it stores the current sp in
+ * k0 and loads the new value in sp.  If not, it clobbers k0 and
+ * stores the new value in k1, leaving sp unaffected.
+ */
 #ifdef CONFIG_SMP
-               .macro  get_saved_sp    /* SMP variation */
+               /* SMP variation */
+               .macro  get_saved_sp docfi=0 tosp=0
                ASM_CPUID_MFC0  k0, ASM_SMP_CPUID_REG
 #if defined(CONFIG_32BIT) || defined(KBUILD_64BIT_SYM32)
                lui     k1, %hi(kernelsp)
@@ -97,7 +105,15 @@
                LONG_SRL        k0, SMP_CPUID_PTRSHIFT
                LONG_ADDU       k1, k0
+               .if \tosp
+               move    k0, sp
+               .if \docfi
+               .cfi_register sp, k0
+               .endif
+               LONG_L  sp, %lo(kernelsp)(k1)
+               .else
                LONG_L  k1, %lo(kernelsp)(k1)
+               .endif
                .macro  set_saved_sp stackp temp temp2
@@ -106,7 +122,8 @@
                LONG_S  \stackp, kernelsp(\temp)
 #else /* !CONFIG_SMP */
-               .macro  get_saved_sp    /* Uniprocessor variation */
+               /* Uniprocessor variation */
+               .macro  get_saved_sp docfi=0 tosp=0
                 * Clear BTB (branch target buffer), forbid RAS (return address
@@ -135,7 +152,15 @@
                daddiu  k1, %hi(kernelsp)
                dsll    k1, k1, 16
+               .if \tosp
+               move    k0, sp
+               .if \docfi
+               .cfi_register sp, k0
+               .endif
+               LONG_L  sp, %lo(kernelsp)(k1)
+               .else
                LONG_L  k1, %lo(kernelsp)(k1)
+               .endif
                .macro  set_saved_sp stackp temp temp2
@@ -151,7 +176,6 @@
                sll     k0, 3           /* extract cu0 bit */
                .set    noreorder
                bltz    k0, 8f
-                move   k1, sp
 #ifdef CONFIG_EVA
                 * Flush interAptiv's Return Prediction Stack (RPS) by writing
@@ -178,17 +202,16 @@
                MTC0    k0, CP0_ENTRYHI
                .set    reorder
+                move   k0, sp
                /* Called from user mode, new stack. */
-8:             move    k0, sp
-               PTR_SUBU sp, k1, PT_SIZE
-               .set    at=k0
-8:             PTR_SUBU k1, PT_SIZE
+               .set    at=k1
+               PTR_SUBU sp, PT_SIZE
                .set    noat
-               move    k0, sp
-               move    sp, k1
                LONG_S  k0, PT_R29(sp)
                LONG_S  $3, PT_R3(sp)
@@ -206,16 +229,16 @@
                LONG_S  $5, PT_R5(sp)
                LONG_S  v1, PT_CAUSE(sp)
                LONG_S  $6, PT_R6(sp)
-               MFC0    v1, CP0_EPC
+               LONG_S  ra, PT_R31(sp)
+               MFC0    ra, CP0_EPC
                LONG_S  $7, PT_R7(sp)
 #ifdef CONFIG_64BIT
                LONG_S  $8, PT_R8(sp)
                LONG_S  $9, PT_R9(sp)
-               LONG_S  v1, PT_EPC(sp)
+               LONG_S  ra, PT_EPC(sp)
                LONG_S  $25, PT_R25(sp)
                LONG_S  $28, PT_R28(sp)
-               LONG_S  $31, PT_R31(sp)
                /* Set thread_info if we're coming from user mode */
                mfc0    k0, CP0_STATUS

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