diff options
author | Eric Fiselier <eric@efcs.ca> | 2018-07-26 00:34:50 +0000 |
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committer | Eric Fiselier <eric@efcs.ca> | 2018-07-26 00:34:50 +0000 |
commit | 6b101f1be13e4b29b854a7a3bdd23783dc987898 (patch) | |
tree | 2e508e75ba8760afcb48878ecf6309d2359d23a7 | |
parent | 104b331e4c280684adca12e42714c47abfba9b01 (diff) |
[libc++] Add hack to allow ubsan to work w/o compiler-rt (__muloti4 is undefined)
Summary:
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
Reviewers: mclow.lists, ldionne, rsmith, jyknight, echristo
Reviewed By: echristo
Subscribers: dberris, cfe-commits
Differential Revision: https://reviews.llvm.org/D49828
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@337990 91177308-0d34-0410-b5e6-96231b3b80d8
-rw-r--r-- | src/experimental/filesystem/int128_builtins.cpp | 55 |
1 files changed, 55 insertions, 0 deletions
diff --git a/src/experimental/filesystem/int128_builtins.cpp b/src/experimental/filesystem/int128_builtins.cpp new file mode 100644 index 000000000..b168bf525 --- /dev/null +++ b/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 |