[GitHub] [incubator-nuttx] pussuw commented on a change in pull request #5782: RISC-V: Implement option to run NuttX in supervisor mode (S-mode)

[GitBox]

pussuw commented on a change in pull request #5782:
URL: https://github.com/apache/incubator-nuttx/pull/5782#discussion_r838498346



##########
File path: arch/risc-v/include/syscall.h
##########
@@ -207,7 +162,15 @@ static inline uintptr_t sys_call0(unsigned int nbr)
 
   asm volatile
     (
+#if defined (CONFIG_ARCH_USE_S_MODE) && defined (__KERNEL__)
+     " addi sp, sp, -16\n"                  /* Make room */
+     " sd   ra, 0(sp)\n"                    /* Save ra */

Review comment:
       Yes, this works for 64-bit only, oversight by me.
   
   The handy macros REGLOAD/REGSTORE are not usable from inline assembly if I'm 
right ?
   It's the same dilemma as is in riscv_swint.c, basically 99% copypaste for 
the function 
   `static void dispatch_syscall(void)`
   
   I could not think of a good way to merge the two implementations. Maybe 
using some kind of stringify macro like is used with this:
   
   ```
   static inline irqstate_t up_irq_save(void)
   {
     irqstate_t flags;
   
     /* Read mstatus & clear machine interrupt enable (MIE) in mstatus */
   
     __asm__ __volatile__
       (
         "csrrc %0, " CSR_XSTR(CSR_STATUS) ", %1\n"
         : "=r" (flags)
         : "r"(STATUS_IE)
         : "memory"
       );
   
     /* Return the previous mstatus value so that it can be restored with
      * up_irq_restore().
      */
   
     return flags;
   }
   ```




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