sscratch cleanup

kernel/proc.h

@@ -31,7 +31,6 @@ extern struct cpu cpus[NCPU];
 // per-process data for the trap handling code in trampoline.S.
 // sits in a page by itself just under the trampoline page in the
 // user page table. not specially mapped in the kernel page table.
-// the sscratch register points here.
 // uservec in trampoline.S saves user registers in the trapframe,
 // then initializes registers from the trapframe's
 // kernel_sp, kernel_hartid, kernel_satp, and jumps to kernel_trap.

kernel/riscv.h

@@ -216,13 +216,6 @@ r_satp()
   return x;
 }
 
-// Supervisor Scratch register, for early trap handler in trampoline.S.
-static inline void 
-w_sscratch(uint64 x)
-{
-  asm volatile("csrw sscratch, %0" : : "r" (x));
-}
-
 static inline void 
 w_mscratch(uint64 x)
 {