Use unguarded loads in stack trace saving

The stack trace saver should see a system state that is not broken.
Therefore use unguarded memory accesses.

However, the unwinder is still haphazard. Terminate immediately if
the program counter or stack pointer look inconsistent.

diff --git a/sys/arch/mips64/mips64/trap.c b/sys/arch/mips64/mips64/trap.c
index 1470522..f4adfb9 100644 (file)
--- a/sys/arch/mips64/mips64/trap.c
+++ b/sys/arch/mips64/mips64/trap.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: trap.c,v 1.157 2022/01/21 16:39:56 visa Exp $ */
+/*     $OpenBSD: trap.c,v 1.158 2022/01/25 07:10:19 visa Exp $ */
 
 /*
  * Copyright (c) 1988 University of Utah.
@@ -1136,6 +1136,9 @@ const char *fn_name(vaddr_t);
 #endif
 void stacktrace_subr(struct trapframe *, int, int (*)(const char*, ...));
 
+extern char kernel_text[];
+extern char etext[];
+
 /*
  * Print a stack backtrace.
  */
@@ -1349,12 +1352,9 @@ loop:
 
 end:
        if (ra) {
-               extern void *kernel_text;
-               extern void *etext;
-
                if (pc == ra && stksize == 0)
                        (*pr)("stacktrace: loop!\n");
-               else if (ra < (vaddr_t)&kernel_text || ra > (vaddr_t)&etext)
+               else if (ra < (vaddr_t)kernel_text || ra > (vaddr_t)etext)
                        (*pr)("stacktrace: ra corrupted!\n");
                else {
                        pc = ra;
@@ -1395,7 +1395,10 @@ stacktrace_save_at(struct stacktrace *st, unsigned int skip)
 
        st->st_count = 0;
        while (st->st_count < STACKTRACE_MAX && pc != 0) {
-               if (!VALID_ADDRESS(pc) || !VALID_ADDRESS(sp))
+               if ((pc & 0x3) != 0 ||
+                   pc < (vaddr_t)kernel_text || pc >= (vaddr_t)etext)
+                       break;
+               if ((sp & 0x7) != 0 || !VALID_ADDRESS(sp))
                        break;
 
                if (!first) {
@@ -1413,6 +1416,8 @@ stacktrace_save_at(struct stacktrace *st, unsigned int skip)
                db_symbol_values(sym, &name, NULL);
                subr = pc - (vaddr_t)diff;
 
+               if ((subr & 0x3) != 0)
+                       break;
                if (subr == (vaddr_t)u_general || subr == (vaddr_t)u_intr)
                        break;
                if (subr == (vaddr_t)k_general || subr == (vaddr_t)k_intr) {
@@ -1430,11 +1435,11 @@ stacktrace_save_at(struct stacktrace *st, unsigned int skip)
                done = 0;
                framesize = 0;
                for (va = subr; va < pc && !done; va += 4) {
-                       inst.word = kdbpeek(va);
+                       inst.word = *(uint32_t *)va;
                        if (inst_call(inst.word) || inst_return(inst.word)) {
                                /* Check the delay slot and stop. */
                                va += 4;
-                               inst.word = kdbpeek(va);
+                               inst.word = *(uint32_t *)va;
                                done = 1;
                        }
                        switch (inst.JType.op) {
@@ -1448,7 +1453,7 @@ stacktrace_save_at(struct stacktrace *st, unsigned int skip)
                        case OP_SD:
                                if (inst.IType.rs == SP &&
                                    inst.IType.rt == RA && ra == 0)
-                                       ra = kdbpeekd(sp +
+                                       ra = *(uint64_t *)(sp +
                                            (int16_t)inst.IType.imm);
                                break;
                        case OP_DADDI: