ARC: pt_regs update #3: Remove unused gutter at start of callee_regs

This is trickier than prev two:

* context switching code saves kernel mode callee regs in the format of
  struct callee_regs thus needs adjustment. This also reduces the height
  of topmost kernel stack frame by 1 word.

* Since kernel stack unwinder is sensitive to height of topmost kernel
  stack frame, that needs a word of adjustment too.

ptrace needs a bit of updating since pt_regs now diverges from
user_regs_struct.

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

9 files changed, 24 insertions, 31 deletions

diff --git a/arch/arc/include/asm/entry.h b/arch/arc/include/asm/entry.h
index 5ff7b8dd3d5b..820202af21a5 100644
--- a/arch/arc/include/asm/entry.h
+++ b/arch/arc/include/asm/entry.h
@@ -124,8 +124,6 @@
         st.a    r25, [sp, -4]
 #endif
 
-        /* move up by 1 word to "create" callee_regs->"stack_place_holder" */
-        sub sp, sp, 4
 .endm
 
 /*--------------------------------------------------------------
@@ -148,10 +146,9 @@
         st.a    r23, [sp, -4]
         st.a    r24, [sp, -4]
 #ifdef CONFIG_ARC_CURR_IN_REG
-        sub     sp, sp, 8
+        sub     sp, sp, 4
 #else
         st.a    r25, [sp, -4]
-        sub     sp, sp, 4
 #endif
 .endm
 
@@ -168,14 +165,11 @@
  *-------------------------------------------------------------*/
 .macro RESTORE_CALLEE_SAVED_KERNEL
 
-
 #ifdef CONFIG_ARC_CURR_IN_REG
-        add     sp, sp, 8  /* skip callee_reg gutter and user r25 placeholder */
+        add     sp, sp, 4  /* skip usual r25 placeholder */
 #else
-        add     sp, sp, 4   /* skip "callee_regs->stack_place_holder" */
         ld.ab   r25, [sp, 4]
 #endif
-
         ld.ab   r24, [sp, 4]
         ld.ab   r23, [sp, 4]
         ld.ab   r22, [sp, 4]
@@ -203,8 +197,6 @@
  *-------------------------------------------------------------*/
 .macro RESTORE_CALLEE_SAVED_USER
 
-        add     sp, sp, 4   /* skip "callee_regs->stack_place_holder" */
-
 #ifdef CONFIG_ARC_CURR_IN_REG
         ld.ab   r12, [sp, 4]
         st      r12, [r25, TASK_THREAD + THREAD_USER_R25]
@@ -230,7 +222,7 @@
  * Super FAST Restore callee saved regs by simply re-adjusting SP
  *-------------------------------------------------------------*/
 .macro DISCARD_CALLEE_SAVED_USER
-        add     sp, sp, 14 * 4
+        add     sp, sp, SZ_CALLEE_REGS
 .endm
 
 /*--------------------------------------------------------------
diff --git a/arch/arc/include/asm/processor.h b/arch/arc/include/asm/processor.h
index 81efbcae3839..8c77e623c4e5 100644
--- a/arch/arc/include/asm/processor.h
+++ b/arch/arc/include/asm/processor.h
@@ -19,6 +19,7 @@
 #ifndef __ASSEMBLY__
 
 #include <asm/arcregs.h>        /* for STATUS_E1_MASK et all */
+#include <asm/ptrace.h>
 
 /* Arch specific stuff which needs to be saved per task.
  * However these items are not so important so as to earn a place in
@@ -75,11 +76,15 @@ unsigned long thread_saved_pc(struct task_struct *t);
 
 /*
  * Where abouts of Task's sp, fp, blink when it was last seen in kernel mode.
- * These can't be derived from pt_regs as that would give correp user-mode val
+ * Look in process.c for details of kernel stack layout
  */
 #define KSTK_ESP(tsk)   (tsk->thread.ksp)
-#define KSTK_BLINK(tsk) (*((unsigned int *)((KSTK_ESP(tsk)) + (13+1+1)*4)))
-#define KSTK_FP(tsk)    (*((unsigned int *)((KSTK_ESP(tsk)) + (13+1)*4)))
+
+#define KSTK_REG(tsk, off)      (*((unsigned int *)(KSTK_ESP(tsk) + \
+                                        sizeof(struct callee_regs) + off)))
+
+#define KSTK_BLINK(tsk) KSTK_REG(tsk, 4)
+#define KSTK_FP(tsk)    KSTK_REG(tsk, 0)
 
 /*
  * Do necessary setup to start up a newly executed thread.
diff --git a/arch/arc/include/asm/ptrace.h b/arch/arc/include/asm/ptrace.h
index 7491bb7428bd..47801ba135b3 100644
--- a/arch/arc/include/asm/ptrace.h
+++ b/arch/arc/include/asm/ptrace.h
@@ -59,7 +59,6 @@ struct pt_regs {
 /* Callee saved registers - need to be saved only when you are scheduled out */
 
 struct callee_regs {
-        long res;       /* Again this is not needed */
         long r25;
         long r24;
         long r23;
diff --git a/arch/arc/include/uapi/asm/ptrace.h b/arch/arc/include/uapi/asm/ptrace.h
index e0e8403f181f..4599109f68f2 100644
--- a/arch/arc/include/uapi/asm/ptrace.h
+++ b/arch/arc/include/uapi/asm/ptrace.h
@@ -38,8 +38,8 @@ struct user_regs_struct {
                 long r12, r11, r10, r9, r8, r7, r6, r5, r4, r3, r2, r1, r0;
                 long sp;
         } scratch;
+        long pad2;
         struct {
-                long pad;
                 long r25, r24, r23, r22, r21, r20;
                 long r19, r18, r17, r16, r15, r14, r13;
         } callee;
diff --git a/arch/arc/kernel/asm-offsets.c b/arch/arc/kernel/asm-offsets.c
index 7dcda7025241..fdcd76532b70 100644
--- a/arch/arc/kernel/asm-offsets.c
+++ b/arch/arc/kernel/asm-offsets.c
@@ -60,5 +60,6 @@ int main(void)
         DEFINE(PT_r6, offsetof(struct pt_regs, r6));
         DEFINE(PT_r7, offsetof(struct pt_regs, r7));
 
+        DEFINE(SZ_CALLEE_REGS, sizeof(struct callee_regs));
         return 0;
 }
diff --git a/arch/arc/kernel/ctx_sw.c b/arch/arc/kernel/ctx_sw.c
index 60844dac6132..34410eb1a308 100644
--- a/arch/arc/kernel/ctx_sw.c
+++ b/arch/arc/kernel/ctx_sw.c
@@ -23,10 +23,6 @@ __switch_to(struct task_struct *prev_task, struct task_struct *next_task)
         unsigned int tmp;
         unsigned int prev = (unsigned int)prev_task;
         unsigned int next = (unsigned int)next_task;
-        int num_words_to_skip = 1;
-#ifdef CONFIG_ARC_CURR_IN_REG
-        num_words_to_skip++;
-#endif
 
         __asm__ __volatile__(
                 /* FP/BLINK save generated by gcc (standard function prologue */
@@ -44,8 +40,9 @@ __switch_to(struct task_struct *prev_task, struct task_struct *next_task)
                 "st.a    r24, [sp, -4]   \n\t"
 #ifndef CONFIG_ARC_CURR_IN_REG
                 "st.a    r25, [sp, -4]   \n\t"
+#else
+                "sub     sp, sp, 4      \n\t"   /* usual r25 placeholder */
 #endif
-                "sub     sp, sp, %4      \n\t"  /* create gutter at top */
 
                 /* set ksp of outgoing task in tsk->thread.ksp */
                 "st.as   sp, [%3, %1]    \n\t"
@@ -76,10 +73,10 @@ __switch_to(struct task_struct *prev_task, struct task_struct *next_task)
 
                 /* start loading it's CALLEE reg file */
 
-                "add    sp, sp, %4     \n\t"    /* skip gutter at top */
-
 #ifndef CONFIG_ARC_CURR_IN_REG
                 "ld.ab   r25, [sp, 4]   \n\t"
+#else
+                "add    sp, sp, 4       \n\t"
 #endif
                 "ld.ab   r24, [sp, 4]   \n\t"
                 "ld.ab   r23, [sp, 4]   \n\t"
@@ -100,8 +97,7 @@ __switch_to(struct task_struct *prev_task, struct task_struct *next_task)
                 /* FP/BLINK restore generated by gcc (standard func epilogue */
 
                 : "=r"(tmp)
-                : "n"((TASK_THREAD + THREAD_KSP) / 4), "r"(next), "r"(prev),
-                  "n"(num_words_to_skip * 4)
+                : "n"((TASK_THREAD + THREAD_KSP) / 4), "r"(next), "r"(prev)
                 : "blink"
         );
 
diff --git a/arch/arc/kernel/process.c b/arch/arc/kernel/process.c
index 949bfd5d62a0..db868db82944 100644
--- a/arch/arc/kernel/process.c
+++ b/arch/arc/kernel/process.c
@@ -55,10 +55,8 @@ asmlinkage void ret_from_fork(void);
  * |     ...        |
  * |    unused      |
  * |                |
- * ------------------  <==== top of Stack (thread.ksp)
- * |   UNUSED 1 word|
  * ------------------
- * |     r25        |
+ * |     r25        |   <==== top of Stack (thread.ksp)
  * ~                ~
  * |    --to--      |   (CALLEE Regs of user mode)
  * |     r13        |
diff --git a/arch/arc/kernel/ptrace.c b/arch/arc/kernel/ptrace.c
index 6e467e3585b0..333238564b67 100644
--- a/arch/arc/kernel/ptrace.c
+++ b/arch/arc/kernel/ptrace.c
@@ -48,6 +48,7 @@ static int genregs_get(struct task_struct *target,
 
         REG_O_ZERO(pad);
         REG_O_CHUNK(scratch, callee, ptregs);
+        REG_O_ZERO(pad2);
         REG_O_CHUNK(callee, efa, cregs);
         REG_O_CHUNK(efa, stop_pc, &target->thread.fault_address);
 
@@ -96,8 +97,9 @@ static int genregs_set(struct task_struct *target,
                         offsetof(struct user_regs_struct, LOC) + 4);
 
         REG_IGNORE_ONE(pad);
-        /* TBD: disallow updates to STATUS32, orig_r8 etc*/
-        REG_IN_CHUNK(scratch, callee, ptregs);  /* pt_regs[bta..orig_r8] */
+        /* TBD: disallow updates to STATUS32 etc*/
+        REG_IN_CHUNK(scratch, pad2, ptregs);    /* pt_regs[bta..sp] */
+        REG_IGNORE_ONE(pad2);
         REG_IN_CHUNK(callee, efa, cregs);       /* callee_regs[r25..r13] */
         REG_IGNORE_ONE(efa);                    /* efa update invalid */
         REG_IN_ONE(stop_pc, &ptregs->ret);      /* stop_pc: PC update */
diff --git a/arch/arc/kernel/stacktrace.c b/arch/arc/kernel/stacktrace.c
index ca0207b9d5b6..f8b7d880304d 100644
--- a/arch/arc/kernel/stacktrace.c
+++ b/arch/arc/kernel/stacktrace.c
@@ -79,7 +79,7 @@ static void seed_unwind_frame_info(struct task_struct *tsk,
                  * assembly code
                  */
                 frame_info->regs.r27 = 0;
-                frame_info->regs.r28 += 64;
+                frame_info->regs.r28 += 60;
                 frame_info->call_frame = 0;
 
         } else {