Left shifts into the sign bit is a kind of overflow, and the
standard chooses to treat left shifts of negative values the
same way.
However, the -fwrapv option modifies the language to one where
integers are defined as two's complement---which also defines
entirely the behavior of shifts. Disable sanitization of left
shifts when -fwrapv is in effect. The same change was proposed
for LLVM at https://llvm.org/bugs/show_bug.cgi?id=25552.
Bootstrapped/regtested x86_64-pc-linux-gnu. Ok for trunk, and for
GCC 5 branch after 5.3 is released?
Thanks,
Paolo
gcc:
PR sanitizer/68418
* c-family/c-ubsan.c (ubsan_instrument_shift): Disable
sanitization of left shifts for wrapping signed types as well.
gcc/testsuite:
PR sanitizer/68418
* gcc.dg/ubsan/c99-wrapv-shift-1.c,
gcc.dg/ubsan/c99-wrapv-shift-2.c: New testcases.