Fix some UBSAN false positives #6115
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jhawthorn
approved these changes
Jul 12, 2022
| @@ -37,6 +37,7 @@ | |||
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| #include "regparse.h" | |||
| #include <stdarg.h> | |||
| #include "internal/sanitizers.h" | |||
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Because of this addition we need to run ruby tool/update-deps --fix (this is the cause of CI failing). It's a little finicky, ping me if you'd prefer I run it to fix the deps 😅.
| @@ -115,7 +115,7 @@ RB_INT2FIX(long i) | |||
| /* :NOTE: VALUE can be wider than long. As j being unsigned, 2j+1 is fully | |||
| * defined. Also it can be compiled into a single LEA instruction. */ | |||
| const unsigned long j = i; | |||
| const unsigned long k = 2 * j + RUBY_FIXNUM_FLAG; | |||
| const unsigned long k = (j << 1) + RUBY_FIXNUM_FLAG; | |||
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(We discussed this a little at work)
It seems like, even though C considers unsigned overflow defined for both << and *, UBSAN checks for overflow on *, but not <<. We figured that this UBSAN behaviour is probably safe to rely on, and doing this avoids having to NO_SANITIZE in this code that is exported in the C extension API.
(The output of gcc and clang w/o UBSAN is identical)
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I tried building ruby with UBSAN and saw some false-positive results for "unsigned integer overflow". These changes fix the false-positives, without changing the behavior of the code.