EricWF created this revision.
EricWF added reviewers: mclow.lists, ldionne, rsmith, jyknight, echristo.
Herald added a subscriber: dberris.
Using __int128_t with UBSAN causes link errors unless compiler-rt is providing
the runtime library.
Specifically ubsan generates calls to __muloti4 but libgcc doesn't provide a
definition.
In order to avoid this, and allow users to continue using sanitized versions of
libc++, this patch introduces a hack.
It adds a cribbed version of the compiler-rt builtin to the libc++ filesystem
sources.
I don't think this approach will work in the long run, but it seems OK for now.
Also see:
https://bugs.llvm.org/show_bug.cgi?id=30643
https://bugs.llvm.org/show_bug.cgi?id=16404
Repository:
rCXX libc++
https://reviews.llvm.org/D49828
Files:
src/experimental/filesystem/int128_builtins.cpp
Index: src/experimental/filesystem/int128_builtins.cpp
===================================================================
--- /dev/null
+++ src/experimental/filesystem/int128_builtins.cpp
@@ -0,0 +1,55 @@
+/*===-- int128_builtins.cpp - Implement __muloti4 --------------------------===
+ *
+ * The LLVM Compiler Infrastructure
+ *
+ * This file is dual licensed under the MIT and the University of Illinois Open
+ * Source Licenses. See LICENSE.TXT for details.
+ *
+ * ===----------------------------------------------------------------------===
+ *
+ * This file implements __muloti4, and is stolen from the compiler_rt library.
+ *
+ * FIXME: we steal and re-compile it into filesystem, which uses __int128_t,
+ * and requires this builtin when sanitized. See llvm.org/PR30643
+ *
+ * ===----------------------------------------------------------------------===
+ */
+#include "__config"
+#include "climits"
+
+#ifndef _LIBCPP_HAS_NO_INT128
+
+__attribute__((no_sanitize("undefined"))) extern "C" __int128_t
+__muloti4(__int128_t a, __int128_t b, int* overflow) {
+ const int N = (int)(sizeof(__int128_t) * CHAR_BIT);
+ const __int128_t MIN = (__int128_t)1 << (N - 1);
+ const __int128_t MAX = ~MIN;
+ *overflow = 0;
+ __int128_t result = a * b;
+ if (a == MIN) {
+ if (b != 0 && b != 1)
+ *overflow = 1;
+ return result;
+ }
+ if (b == MIN) {
+ if (a != 0 && a != 1)
+ *overflow = 1;
+ return result;
+ }
+ __int128_t sa = a >> (N - 1);
+ __int128_t abs_a = (a ^ sa) - sa;
+ __int128_t sb = b >> (N - 1);
+ __int128_t abs_b = (b ^ sb) - sb;
+ if (abs_a < 2 || abs_b < 2)
+ return result;
+ if (sa == sb) {
+ if (abs_a > MAX / abs_b)
+ *overflow = 1;
+ } else {
+ if (abs_a > MIN / -abs_b)
+ *overflow = 1;
+ }
+ return result;
+}
+
+#endif
Index: src/experimental/filesystem/int128_builtins.cpp
===================================================================
--- /dev/null
+++ src/experimental/filesystem/int128_builtins.cpp
@@ -0,0 +1,55 @@
+/*===-- int128_builtins.cpp - Implement __muloti4 --------------------------===
+ *
+ * The LLVM Compiler Infrastructure
+ *
+ * This file is dual licensed under the MIT and the University of Illinois Open
+ * Source Licenses. See LICENSE.TXT for details.
+ *
+ * ===----------------------------------------------------------------------===
+ *
+ * This file implements __muloti4, and is stolen from the compiler_rt library.
+ *
+ * FIXME: we steal and re-compile it into filesystem, which uses __int128_t,
+ * and requires this builtin when sanitized. See llvm.org/PR30643
+ *
+ * ===----------------------------------------------------------------------===
+ */
+#include "__config"
+#include "climits"
+
+#ifndef _LIBCPP_HAS_NO_INT128
+
+__attribute__((no_sanitize("undefined"))) extern "C" __int128_t
+__muloti4(__int128_t a, __int128_t b, int* overflow) {
+ const int N = (int)(sizeof(__int128_t) * CHAR_BIT);
+ const __int128_t MIN = (__int128_t)1 << (N - 1);
+ const __int128_t MAX = ~MIN;
+ *overflow = 0;
+ __int128_t result = a * b;
+ if (a == MIN) {
+ if (b != 0 && b != 1)
+ *overflow = 1;
+ return result;
+ }
+ if (b == MIN) {
+ if (a != 0 && a != 1)
+ *overflow = 1;
+ return result;
+ }
+ __int128_t sa = a >> (N - 1);
+ __int128_t abs_a = (a ^ sa) - sa;
+ __int128_t sb = b >> (N - 1);
+ __int128_t abs_b = (b ^ sb) - sb;
+ if (abs_a < 2 || abs_b < 2)
+ return result;
+ if (sa == sb) {
+ if (abs_a > MAX / abs_b)
+ *overflow = 1;
+ } else {
+ if (abs_a > MIN / -abs_b)
+ *overflow = 1;
+ }
+ return result;
+}
+
+#endif
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