[llvm-bugs] [Bug 27271] New: UBSAN fails to catch shifts by more than 1<<32

via llvm-bugs llvm-bugs at lists.llvm.org
Thu Apr 7 14:58:24 PDT 2016


            Bug ID: 27271
           Summary: UBSAN fails to catch shifts by more than 1<<32
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: cherepan at mccme.ru
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

UBSAN doesn't warn about this program:

int main(int c, char **v) { 1 << ((long)c << 32); }

Run as `clang -Wno-unused-value -fsanitize=undefined example.c && ./a.out`.
Tested with clang version 3.9.0 (trunk 265708) on x86-64.

gcc6 warns:
example.c:1:31: runtime error: shift exponent 4294967296 is too large for
32-bit type 'int'

Looking at IR, it seems the right operand of the shift is checked only after
it's truncated to 32-bit. This is too late.

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