[GitHub] [incubator-nuttx] pkarashchenko commented on a change in pull request #5506: arch/armv7-a/r: unify switch context from software interrupt

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

pkarashchenko commented on a change in pull request #5506:
URL: https://github.com/apache/incubator-nuttx/pull/5506#discussion_r811915779



##########
File path: arch/arm/src/arm/arm_fullcontextrestore.S
##########
@@ -60,38 +63,14 @@
 	.type	arm_fullcontextrestore, function
 arm_fullcontextrestore:
 
-	/* On entry, a1 (r0) holds address of the register save area.  All other
-	 * registers are available for use.
-	 */
-
-	/* Recover all registers except for r0, r1, R15, and CPSR */
-
-	add	r1, r0, #(4*REG_R2)	/* Offset to REG_R2 storage */
-	ldmia	r1, {r2-r14}		/* Recover registers */
-
-	/* Create a stack frame to hold the some registers */
-
-	sub	sp, sp, #(3*4)		/* Frame for three registers */
-	ldr	r1, [r0, #(4*REG_R0)]	/* Fetch the stored r0 value */
-	str	r1, [sp]		/* Save it at the top of the stack */
-	ldr	r1, [r0, #(4*REG_R1)]	/* Fetch the stored r1 value */
-	str	r1, [sp, #4]		/* Save it in the stack */
-	ldr	r1, [r0, #(4*REG_PC)]	/* Fetch the stored pc value */
-	str	r1, [sp, #8]		/* Save it at the bottom of the frame */
-
-	/* Now we can restore the CPSR.  We wait until we are completely
-	 * finished with the context save data to do this. Restore the CPSR
-	 * may re-enable and interrupts and we could be in a context
-	 * where the save structure is only protected by interrupts being
-	 * disabled.
-	 */
-
-	ldr	r1, [r0, #(4*REG_CPSR)]	/* Fetch the stored CPSR value */
-	msr	spsr_cxsf, r1		/* Set the SPSR */
+	/* Perform the System call with R0=1 and R1=regs */
 
-	/* Now recover r0-r1, pc and cpsr, destroying the stack frame */
+	mov		r1, r0				/* R1: regs */
+	mov		r0, #SYS_restore_context	/* R0: restore context */
+	svc		#SYS_syscall			/* Force synchronous SVCall (or Hard Fault) */
 
-	ldmia	sp!, {r0-r1, r15}^
+	/* This call should not return */
 
+	bx		lr				/* Unnecessary ... will not return */

Review comment:
       Should we branch to `lr` or to some fault handler if call returns unexpectedly?




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