[GitHub] [incubator-nuttx] pkarashchenko commented on a change in pull request #5558: armv7-a/r: fix SVC's sp restore in arm_vectors.S

[GitBox <gi...@apache.org>]

pkarashchenko commented on a change in pull request #5558:
URL: https://github.com/apache/incubator-nuttx/pull/5558#discussion_r824257401



##########
File path: arch/arm/src/armv7-a/arm_vectors.S
##########
@@ -239,15 +239,16 @@ arm_vectorirq:
 	cmp		r2, #PSR_MODE_USR		/* User mode? */
 	bne		.Lirqleavesvc			/* Branch if not user mode */
 
+	add		sp, sp, #XCPTCONTEXT_SIZE	/* Restore SVC's sp */
+
 	/* ldmia with ^ will return the user mode registers (provided that r15
 	 * is not in the register list).
 	 */
 
-	mov		r13, r0				/* (SVC) R13=Register storage area */
-	ldmia		r13, {r0-r12}			/* Restore common R0-R12 */
-	add		r14, r13, #(4*REG_R13)		/* (SVC) R14=address of R13/R14 storage */
-	ldmia		r14, {r13, r14}^		/* Restore user mode R13/R14 */
-	add		r14, r13, #(4*REG_R15)		/* (SVC) R14=address of R15 storage */
+	mov		r14, r0				/* (SVC) r14=Register storage area */
+	ldmia		r14!, {r0-r12}			/* Restore common r0-r12 */
+	ldmia		r14, {r13, r14}^		/* Restore user mode r13/r14 */

Review comment:
       Why we can't just `ldmia r14, {r13, r14, r15}^` here instead of
   ```
   	ldmia		r14, {r13, r14}^		/* Restore user mode r13/r14 */
   	add		r14, r14, #(4*2)		/* (SVC) r14=address of r15 storage */
   	ldmia r14, {r15}^ /* Return */
   ```
   I see that PC was stored right after LR
   ```
   sub r3, lr, #4
   ...
   add r0, sp, #(4*REG_SP) /* Offset to sp/lr storage */
   stmia r0, {r13, r14}^ /* Save user mode r13(sp) and r14(lr) */
   add r0, sp, #(4*REG_R15) /* Offset to pc/cpsr storage */
   stmia r0, {r3, r4} /* Save r15(pc), and the CPSR */
   ```
   Or I'm missing something?




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