ARC: pt_regs update #2: Remove unused gutter at start of pt_regs

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

Author: vineetgarc

arch/arc/include/asm/entry.h

@@ -432,9 +432,6 @@
 	st.a    r9, [sp, -4]
 	lr	r9, [erbta]
 	st.a    r9, [sp, -4]
-
-	/* move up by 1 word to "create" pt_regs->"stack_place_holder" */
-	sub sp, sp, 4
 .endm
 
 /*--------------------------------------------------------------
@@ -474,9 +471,6 @@
  * by hardware and that is not good.
  *-------------------------------------------------------------*/
 .macro RESTORE_ALL_SYS
-
-	add sp, sp, 4       /* hop over unused "pt_regs->stack_place_holder" */
-
 	ld.ab   r9, [sp, 4]
 	sr	r9, [erbta]
 	ld.ab   r9, [sp, 4]
@@ -530,9 +524,6 @@
 	st.a    r9, [sp, -4]
 	lr	r9, [bta_l1]
 	st.a    r9, [sp, -4]
-
-	/* move up by 1 word to "create" pt_regs->"stack_place_holder" */
-	sub sp, sp, 4
 .endm
 
 .macro SAVE_ALL_INT2
@@ -561,9 +552,6 @@
 	st.a    r9, [sp, -4]
 	lr	r9, [bta_l2]
 	st.a    r9, [sp, -4]
-
-	/* move up by 1 word to "create" pt_regs->"stack_place_holder" */
-	sub sp, sp, 4
 .endm
 
 /*--------------------------------------------------------------
@@ -577,8 +565,6 @@
  *-------------------------------------------------------------*/
 
 .macro RESTORE_ALL_INT1
-	add sp, sp, 4       /* hop over unused "pt_regs->stack_place_holder" */
-
 	ld.ab   r9, [sp, 4] /* Actual reg file */
 	sr	r9, [bta_l1]
 	ld.ab   r9, [sp, 4]
@@ -601,8 +587,6 @@
 .endm
 
 .macro RESTORE_ALL_INT2
-	add sp, sp, 4       /* hop over unused "pt_regs->stack_place_holder" */
-
 	ld.ab   r9, [sp, 4]
 	sr	r9, [bta_l2]
 	ld.ab   r9, [sp, 4]

arch/arc/include/asm/ptrace.h

@@ -17,12 +17,6 @@
 /* THE pt_regs: Defines how regs are saved during entry into kernel */
 
 struct pt_regs {
-	/*
-	 * 1 word gutter after reg-file has been saved
-	 * Technically not needed, Since SP always points to a "full" location
-	 * (vs. "empty"). But pt_regs is shared with tools....
-	 */
-	long res;
 
 	/* Real registers */
 	long bta;	/* bta_l1, bta_l2, erbta */

arch/arc/include/uapi/asm/ptrace.h

@@ -20,16 +20,19 @@
  *
  * This is to decouple pt_regs from user-space ABI, to be able to change it
  * w/o affecting the ABI.
- * Although the layout (initial padding) is similar to pt_regs to have some
- * optimizations when copying pt_regs to/from user_regs_struct.
+ *
+ * The intermediate pad,pad2 are relics of initial layout based on pt_regs
+ * for optimizations when copying pt_regs to/from user_regs_struct.
+ * We no longer need them, but can't be changed as they are part of ABI now.
  *
  * Also, sigcontext only care about the scratch regs as that is what we really
- * save/restore for signal handling.
+ * save/restore for signal handling. However gdb also uses the same struct
+ * hence callee regs need to be in there too.
 */
 struct user_regs_struct {
 
+	long pad;
 	struct {
-		long pad;
 		long bta, lp_start, lp_end, lp_count;
 		long status32, ret, blink, fp, gp;
 		long r12, r11, r10, r9, r8, r7, r6, r5, r4, r3, r2, r1, r0;

arch/arc/kernel/ptrace.c

@@ -40,6 +40,13 @@ static int genregs_get(struct task_struct *target,
 			offsetof(struct user_regs_struct, LOC), \
 			offsetof(struct user_regs_struct, LOC) + 4);
 
+#define REG_O_ZERO(LOC)		\
+	if (!ret)		\
+		ret = user_regset_copyout_zero(&pos, &count, &kbuf, &ubuf, \
+			offsetof(struct user_regs_struct, LOC), \
+			offsetof(struct user_regs_struct, LOC) + 4);
+
+	REG_O_ZERO(pad);
 	REG_O_CHUNK(scratch, callee, ptregs);
 	REG_O_CHUNK(callee, efa, cregs);
 	REG_O_CHUNK(efa, stop_pc, &target->thread.fault_address);
@@ -88,6 +95,7 @@ static int genregs_set(struct task_struct *target,
 			offsetof(struct user_regs_struct, LOC), \
 			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] */
 	REG_IN_CHUNK(callee, efa, cregs);	/* callee_regs[r25..r13] */