6068 libdisasm: previnstr arch op should have a sane default
Reviewed by: Robert Mustacchi <rm@joyent.com>

@@ -170,61 +170,10 @@
 dis_i386_min_instrlen(dis_handle_t *dhp)
 {
         return (1);
 }
 
-/*
- * Return the previous instruction.  On x86, we have no choice except to
- * disassemble everything from the start of the symbol, and stop when we have
- * reached our instruction address.  If we're not in the middle of a known
- * symbol, then we return the same address to indicate failure.
- */
-static uint64_t
-dis_i386_previnstr(dis_handle_t *dhp, uint64_t pc, int n)
-{
-        uint64_t *hist, addr, start;
-        int cur, nseen;
-        uint64_t res = pc;
-
-        if (n <= 0)
-                return (pc);
-
-        if (dhp->dh_lookup(dhp->dh_data, pc, NULL, 0, &start, NULL) != 0 ||
-            start == pc)
-                return (res);
-
-        hist = dis_zalloc(sizeof (uint64_t) * n);
-
-        for (cur = 0, nseen = 0, addr = start; addr < pc; addr = dhp->dh_addr) {
-                hist[cur] = addr;
-                cur = (cur + 1) % n;
-                nseen++;
-
-                /* if we cannot make forward progress, give up */
-                if (dis_disassemble(dhp, addr, NULL, 0) != 0)
-                        goto done;
-        }
-
-        if (addr != pc) {
-                /*
-                 * We scanned past %pc, but didn't find an instruction that
-                 * started at %pc.  This means that either the caller specified
-                 * an invalid address, or we ran into something other than code
-                 * during our scan.  Virtually any combination of bytes can be
-                 * construed as a valid Intel instruction, so any non-code bytes
-                 * we encounter will have thrown off the scan.
-                 */
-                goto done;
-        }
-
-        res = hist[(cur + n - MIN(n, nseen)) % n];
-
-done:
-        dis_free(hist, sizeof (uint64_t) * n);
-        return (res);
-}
-
 static int
 dis_i386_supports_flags(int flags)
 {
         int archflags = flags & DIS_ARCH_MASK;
 

@@ -247,10 +196,9 @@
 dis_arch_t dis_arch_i386 = {
         .da_supports_flags      = dis_i386_supports_flags,
         .da_handle_attach       = dis_i386_handle_attach,
         .da_handle_detach       = dis_i386_handle_detach,
         .da_disassemble         = dis_i386_disassemble,
-        .da_previnstr           = dis_i386_previnstr,
         .da_min_instrlen        = dis_i386_min_instrlen,
         .da_max_instrlen        = dis_i386_max_instrlen,
         .da_instrlen            = dis_i386_instrlen,
 };