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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)