[GitHub] [incubator-nuttx] pussuw commented on a change in pull request #5917: arch/risc-v: move REGLOAD/REGSTORE macro to riscv_internal.h

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

pussuw commented on a change in pull request #5917:
URL: https://github.com/apache/incubator-nuttx/pull/5917#discussion_r838715537



##########
File path: arch/risc-v/src/common/riscv_swint.c
##########
@@ -109,45 +109,24 @@ static void riscv_registerdump(const uintptr_t *regs)
 
 #ifdef CONFIG_LIB_SYSCALL
 static void dispatch_syscall(void) naked_function;
-#ifdef CONFIG_ARCH_RV64
 static void dispatch_syscall(void)
 {
   asm volatile
     (
-     " addi sp, sp, -8\n"         /* Create a stack frame to hold ra */
-     " sd   ra, 0(sp)\n"          /* Save ra in the stack frame */
-     " la   t0, g_stublookup\n"   /* t0=The base of the stub lookup table */
-     " slli a0, a0, 3\n"          /* a0=Offset for the stub lookup table */
-     " add  t0, t0, a0\n"         /* t0=The address in the table */
-     " ld   t0, 0(t0)\n"          /* t0=The address of the stub for this syscall */
-     " jalr ra, t0\n"             /* Call the stub (modifies ra) */
-     " ld   ra, 0(sp)\n"          /* Restore ra */
-     " addi sp, sp, 8\n"          /* Destroy the stack frame */
-     " mv   a2, a0\n"             /* a2=Save return value in a0 */
-     " li   a0, 3\n"              /* a0=SYS_syscall_return (3) */
-     " ecall"                     /* Return from the syscall */
+     "addi sp, sp, -" REGSSIZE "\n" /* Create a stack frame to hold ra */

Review comment:
       Using the register size here is incorrect. The stack pointer has separate alignment requirements, and in this case a 16B alignment should be ensured, if FPU is in use, if I remember correctly. 
   
   It is IMO simpler to just make a 16B stack frame here. Every other place I could find does this, and this is what I did for the S-mode patch too. There is a macro for this too in riscv_internal.h `STACK_ALIGNMENT`




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