On Mon, Aug 28, 2023 at 12:33 AM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: > > Hi Linus, > > On Sat, Aug 26, 2023 at 3:08 AM Linus Torvalds > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Fri, 25 Aug 2023 at 17:52, Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote: > > And quite often we simply use other names - but then we also do *not* > > build with -freestanding, because -freestanding has at least > > traditionally meant that the compiler won't optimize the simple and > > obvious cases (typically things like "memcpy with a constant size"). > > Several architectures (incl. x86, but excl. amd64) do build the kernel with > -freestanding. > > IIRC, the issue was that without that, gcc was "optimizing" calls > to standard functions (implemented as inline optimized assembler > functions) by replacing them with calls to other standard functions > (also implemented as inline optimized assembler functions). As the > latter became external calls, this defeated the optimized assembler > implementation, and could even cause build failures if no external > implementation was available. That's what the -fno-builtin-* flags are for, IMO, though those also have toolchain portability issues IME. -- Thanks, ~Nick Desaulniers
