On Tue, 4 Jul 2023 at 16:52, Philippe Mathieu-Daudé <phi...@linaro.org> wrote: > > On 4/7/23 17:43, Peter Maydell wrote: > > If you build QEMU with the clang sanitizer enabled, you can see it > > fire when running the arm-cpu-features test: > > > > $ QTEST_QEMU_BINARY=./build/arm-clang/qemu-system-aarch64 > > ./build/arm-clang/tests/qtest/arm-cpu-features > > [...] > > ../../target/arm/cpu64.c:125:19: runtime error: shift exponent 64 is too > > large for 64-bit type 'unsigned long long' > > [...] > > > > This happens because the user can specify some incorrect SVE > > properties that result in our calculating a max_vq of 0. We catch > > this and error out, but before we do that we calculate > > > > vq_mask = MAKE_64BIT_MASK(0, max_vq);$ > > > > and the MAKE_64BIT_MASK() call is only valid for lengths that are > > greater than zero, so we hit the undefined behaviour. > > Can we fix it generically? > > -- >8 -- > --- a/include/qemu/bitops.h > +++ b/include/qemu/bitops.h > @@ -28,3 +28,3 @@ > #define MAKE_64BIT_MASK(shift, length) \ > - (((~0ULL) >> (64 - (length))) << (shift)) > + ((length) ? (((~0ULL) >> (64 - (length))) << (shift)) : 0) > > ---
Only by introducing a conditional in the case where the length isn't a compile time constant. Like the extract and deposit functions, the assumption is that you're operating on a field that actually exists and isn't zero-width. thanks -- PMM
