Use __builtin_frame_address() instead of "sp" directly.

Also use pointer arithmetic on char * instead of void *.

machine/mtrap.h

@@ -48,18 +48,13 @@ typedef struct {
   volatile uint32_t* plic_s_ie;
 } hls_t;
 
-#define STACK_POINTER() ({            \
-  uintptr_t __sp;                     \
-  __asm__("mv %0, sp" : "=r"(__sp));  \
-  __sp;                               \
-})
-
-#define MACHINE_STACK_TOP()           \
-  ({ (void*)((STACK_POINTER() + RISCV_PGSIZE) & -RISCV_PGSIZE); })
+#define MACHINE_STACK_TOP() ({ \
+  uintptr_t sp = (uintptr_t)__builtin_frame_address(0) ; \
+  (char *)((sp + RISCV_PGSIZE) & -RISCV_PGSIZE); })
 
 // hart-local storage, at top of stack
 #define HLS() ((hls_t*)(MACHINE_STACK_TOP() - HLS_SIZE))
-#define OTHER_HLS(id) ((hls_t*)((void*)HLS() + RISCV_PGSIZE * ((id) - read_const_csr(mhartid))))
+#define OTHER_HLS(id) ((hls_t*)((char*)HLS() + RISCV_PGSIZE * ((id) - read_const_csr(mhartid))))
 
 hls_t* hls_init(uintptr_t hart_id);
 void parse_config_string();