platform: riscv64: fix building with -fno-omit-frame-pointer

Register s0 is the frame-pointer register and must be handled
separately.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

src/greenlet/platform/switch_riscv_unix.h

@@ -3,28 +3,32 @@
 #ifdef SLP_EVAL
 #define STACK_MAGIC 0
 
-#define REGS_TO_SAVE "s0", "s1", "s2", "s3", "s4", "s5", \
+#define REGS_TO_SAVE "s1", "s2", "s3", "s4", "s5", \
 		     "s6", "s7", "s8", "s9", "s10", "s11", "fs0", "fs1", \
 		     "fs2", "fs3", "fs4", "fs5", "fs6", "fs7", "fs8", "fs9", \
 		     "fs10", "fs11"
 
 static int
 slp_switch(void)
 {
+  long fp;
   int ret;
   long *stackref, stsizediff;
   __asm__ volatile ("" : : : REGS_TO_SAVE);
+  __asm__ volatile ("mv %0, fp" : "=r" (fp) : );
   __asm__ volatile ("mv %0, sp" : "=r" (stackref) : );
   {
       SLP_SAVE_STATE(stackref, stsizediff);
       __asm__ volatile (
 	  "add sp, sp, %0\n\t"
+	  "add fp, fp, %0\n\t"
 	  : /* no outputs */
 	  : "r" (stsizediff)
 	  );
       SLP_RESTORE_STATE();
   }
   __asm__ volatile ("" : : : REGS_TO_SAVE);
+  __asm__ volatile ("ld fp, %0" : : "m" (fp));
   __asm__ volatile ("mv %0, zero" : "=r" (ret) : );
   return ret;
 }