Messages in this thread | | | From | Michael Ellerman <> | Subject | Re: [PATCH 00/10] raise minimum GCC version to 5.1 | Date | Sat, 11 Sep 2021 20:42:49 +1000 |
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Kees Cook <keescook@chromium.org> writes: > On Fri, Sep 10, 2021 at 04:40:37PM -0700, Nick Desaulniers wrote: >> commit fad7cd3310db ("nbd: add the check to prevent overflow in >> __nbd_ioctl()") >> >> raised an issue from the fallback helpers added in >> >> commit f0907827a8a9 ("compiler.h: enable builtin overflow checkers and add fallback code") >> >> Specifically, the helpers for checking whether the results of a >> multiplication overflowed (__unsigned_mul_overflow, >> __signed_add_overflow) use the division operator when >> !COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW. This is problematic for 64b >> operands on 32b hosts. >> >> Also, because the macro is type agnostic, it is very difficult to write >> a similarly type generic macro that dispatches to one of: >> * div64_s64 >> * div64_u64 >> * div_s64 >> * div_u64 > > Given that it's all compile-time type-aware goo, this isn't so bad. The > gist[1] you linked off the bug report is pretty close. Needs some > bikeshedding. ;) > >> Raising the minimum supported versions allows us to remove all of the >> fallback helpers for !COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW, instead >> dispatching the compiler builtins. >> >> arm64 has already raised the minimum supported GCC version to 5.1, do >> this for all targets now. See the link below for the previous >> discussion. > > That said, I'd much prefer raising the minimum GCC -- no one appears > to actually be building on 4.9 -- there are close to 200 errors (neé > warnings) on x86_64 allmodconfig there currently.
I still do 4.9 builds on kisskb, but I agree there are a lot of warnings, and no one ever has time to fix any.
cheers
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