On 23/03/2021 13.14, Andrew Jones wrote:
On Mon, Mar 22, 2021 at 09:35:23AM +0100, Andrew Jones wrote:@@ -208,23 +209,46 @@ unsigned long int strtoul(const char *nptr, char **endptr, int base) c = *s - 'A' + 10; else break; - acc = acc * base + c; + + if (is_signed) { + long __acc = (long)acc; + overflow = __builtin_smull_overflow(__acc, base, &__acc); + assert(!overflow); + overflow = __builtin_saddl_overflow(__acc, c, &__acc); + assert(!overflow); + acc = (unsigned long)__acc; + } else { + overflow = __builtin_umull_overflow(acc, base, &acc); + assert(!overflow); + overflow = __builtin_uaddl_overflow(acc, c, &acc); + assert(!overflow); + } +Unfortunately my use of these builtins isn't loved by older compilers, like the one used by the build-centos7 pipeline in our gitlab CI. I could wrap them in an #if GCC_VERSION >= 50100 and just have the old 'acc = acc * base + c' as the fallback, but that's not pretty and would also mean that clang would use the fallback too. Maybe we can try and make our compiler.h more fancy in order to provide a COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW define like linux does for both gcc and clang. Or, we could just forgot the overflow checking. Anybody else have suggestions? Paolo? Thomas?
What does a "normal" libc implementation do (e.g. glibc)? If it is also not doing overflow checking, I think we also don't need it in the kvm-unit-tests.
Thomas
