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6068 libdisasm: previnstr arch op should have a sane default
Reviewed by: Robert Mustacchi <rm@joyent.com>
*** 194,206 ****
--- 194,264 ----
dis_disassemble(dis_handle_t *dhp, uint64_t addr, char *buf, size_t buflen)
{
return (dhp->dh_arch->da_disassemble(dhp, addr, buf, buflen));
}
+ /*
+ * On some instruction sets (e.g., 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_generic_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);
+ }
+
+ /*
+ * Return the nth previous instruction's address. Return the same address
+ * to indicate failure.
+ */
uint64_t
dis_previnstr(dis_handle_t *dhp, uint64_t pc, int n)
{
+ if (dhp->dh_arch->da_previnstr == NULL)
+ return (dis_generic_previnstr(dhp, pc, n));
+
return (dhp->dh_arch->da_previnstr(dhp, pc, n));
}
int
dis_min_instrlen(dis_handle_t *dhp)