riscv: Add instruction dump to RISC-V splats

Add instruction dump (Code:) output to RISC-V splats. Dump 16b
parcels.

An example:
  Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
  Oops [#1]
  Modules linked in:
  CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.2.0-rc3-00302-g840ff44c571d-dirty #27
  Hardware name: riscv-virtio,qemu (DT)
  epc : kernel_init+0xc8/0x10e
   ra : kernel_init+0x70/0x10e
  epc : ffffffff80bd9a40 ra : ffffffff80bd99e8 sp : ff2000000060bec0
   gp : ffffffff81730b28 tp : ff6000007ff00000 t0 : 7974697275636573
   t1 : 0000000000000000 t2 : 3030303270393d6e s0 : ff2000000060bee0
   s1 : ffffffff81732028 a0 : 0000000000000000 a1 : ff60000080dd1780
   a2 : 0000000000000002 a3 : ffffffff8176a470 a4 : 0000000000000000
   a5 : 000000000000000a a6 : 0000000000000081 a7 : ff60000080dd1780
   s2 : 0000000000000000 s3 : 0000000000000000 s4 : 0000000000000000
   s5 : 0000000000000000 s6 : 0000000000000000 s7 : 0000000000000000
   s8 : 0000000000000000 s9 : 0000000000000000 s10: 0000000000000000
   s11: 0000000000000000 t3 : ffffffff81186018 t4 : 0000000000000022
   t5 : 000000000000003d t6 : 0000000000000000
  status: 0000000200000120 badaddr: 0000000000000000 cause: 000000000000000f
  [<ffffffff80003528>] ret_from_exception+0x0/0x16
  Code: 862a d179 608c a517 0069 0513 2be5 d0ef db2e 47a9 (c11c) a517
  ---[ end trace 0000000000000000 ]---
  Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
  SMP: stopping secondary CPUs
  ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b ]---

Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
Link: https://lore.kernel.org/r/20230119074738.708301-2-bjorn@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index 549bde5c970a13e9412148c7c45aca1ef2034825..fbdcdbc792d37bd618d1a148ab154829d492912d 100644 (file)
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -29,6 +29,27 @@ int show_unhandled_signals = 1;
 
 static DEFINE_SPINLOCK(die_lock);
 
+static void dump_kernel_instr(const char *loglvl, struct pt_regs *regs)
+{
+       char str[sizeof("0000 ") * 12 + 2 + 1], *p = str;
+       const u16 *insns = (u16 *)instruction_pointer(regs);
+       long bad;
+       u16 val;
+       int i;
+
+       for (i = -10; i < 2; i++) {
+               bad = get_kernel_nofault(val, &insns[i]);
+               if (!bad) {
+                       p += sprintf(p, i == 0 ? "(%04hx) " : "%04hx ", val);
+               } else {
+                       printk("%sCode: Unable to access instruction at 0x%px.\n",
+                              loglvl, &insns[i]);
+                       return;
+               }
+       }
+       printk("%sCode: %s\n", loglvl, str);
+}
+
 void die(struct pt_regs *regs, const char *str)
 {
        static int die_counter;
@@ -43,8 +64,10 @@ void die(struct pt_regs *regs, const char *str)
 
        pr_emerg("%s [#%d]\n", str, ++die_counter);
        print_modules();
-       if (regs)
+       if (regs) {
                show_regs(regs);
+               dump_kernel_instr(KERN_EMERG, regs);
+       }
 
        cause = regs ? regs->cause : -1;
        ret = notify_die(DIE_OOPS, str, regs, 0, cause, SIGSEGV);