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charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, 20 Feb 2024 at 08:55, Ard Biesheuvel wrote: > > On Mon, 19 Feb 2024 at 19:22, Mark Rutland wrote: > > > > On Mon, Feb 19, 2024 at 06:06:19PM +0100, Arnd Bergmann wrote: > > > On Mon, Feb 19, 2024, at 16:41, Ard Biesheuvel wrote: > > > > On Mon, 19 Feb 2024 at 15:43, Geert Uytterhoeven wrote: > > > >> On Mon, Feb 19, 2024 at 11:57=E2=80=AFAM Ard Biesheuvel wrote: > > > >> > On Mon, 19 Feb 2024 at 11:56, Ard Biesheuvel w= rote: > > > > > > >> > https://godbolt.org/z/GTnf3vPaT > > > >> > > > >> I could reproduce the issue on v6.8-rc5 using arm64 defconfig > > > >> and x86_64-gcc-5.5.0-nolibc-aarch64-linux.tar.xz from > > > >> https://cdn.kernel.org/pub/tools/crosstool/files/bin/x86_64/5.5.0/= : > > > >> > > > > > > > > OK, I managed to do so as well. > > > > > > > > And GCC 6.4 from the same source works correctly. > > > > > > > > Not sure whether there are any plans to bump the minimal GCC versio= n > > > > any time soon (cc'ing Arnd), but we should probably drop this chang= e > > > > until that happens. > > > > > > From what I can tell, we may as well formally raise the minimum > > > gcc version to 8.1+ already, as that is a version that is > > > actually used in distros, and we have been on 5.1+ for a few > > > years already. > > > > > > Not sure if there are any other benefits to gcc-8 besides > > > allowing minor cleanups. > > > > Arguably a minor cleanup, but on arm64 that'd allow us to get rid of th= e old > > mcount-based ftrace implementation and rely on -fpatchable-function-ent= ry. > > On its own that'd save ~130 lines of asm and ~70 lines of C, but it'd a= lso > > remove some constraints on other features (e.g. the mcount-based form's= graph > > tracer isn't compatible with pointer authentication), it would simplify= a few > > things going forwards (e.g. the implementation of RELIABLE_STACKTRACE, = since we > > could rely on having ftrace_regs and a single trampoline), and the rema= ining > > support would be better tested. > > > > I've wanted to remove the old ftrace implementation for a while, but on= its own > > it was never important/urgent enough to justify bumping to GCC 8+. > > > > I don't think this is minor, tbh. Supporting two versions of the > highly complex tracing infrastructure for a toolchain that is only > used in CI seems like a waste of time and effort. > > I checked x86, and it needs at least GCC 7 for retpoline support, so I > reckon at least GCC 5/6 support might be dropped there as well. Another data point: __GCC_ASM_FLAG_OUTPUTS__ needs GCC 6 or later on x86. 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