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Date: Tue, 27 Oct 2020 20:25:26 +0100 From: Geert Uytterhoeven <geert@...ux-m68k.org> To: Nick Desaulniers <ndesaulniers@...gle.com> Cc: Ard Biesheuvel <ardb@...nel.org>, Kees Cook <keescook@...omium.org>, Ingo Molnar <mingo@...nel.org>, Catalin Marinas <catalin.marinas@....com>, Mark Rutland <mark.rutland@....com>, Peter Collingbourne <pcc@...gle.com>, James Morse <james.morse@....com>, Borislav Petkov <bp@...e.de>, Ingo Molnar <mingo@...hat.com>, Russell King <linux@...linux.org.uk>, Masahiro Yamada <masahiroy@...nel.org>, Arvind Sankar <nivedita@...m.mit.edu>, Nathan Chancellor <natechancellor@...il.com>, Arnd Bergmann <arnd@...db.de>, "the arch/x86 maintainers" <x86@...nel.org>, clang-built-linux <clang-built-linux@...glegroups.com>, Linux-Arch <linux-arch@...r.kernel.org>, linux-efi <linux-efi@...r.kernel.org>, Linux ARM <linux-arm-kernel@...ts.infradead.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Linux-Renesas <linux-renesas-soc@...r.kernel.org>, Josh Poimboeuf <jpoimboe@...hat.com> Subject: Re: [PATCH v6 13/29] arm64/build: Assert for unwanted sections Hi Nick, CC Josh On Mon, Oct 26, 2020 at 6:49 PM Nick Desaulniers <ndesaulniers@...gle.com> wrote: > On Mon, Oct 26, 2020 at 10:44 AM Geert Uytterhoeven > <geert@...ux-m68k.org> wrote: > > On Mon, Oct 26, 2020 at 6:39 PM Ard Biesheuvel <ardb@...nel.org> wrote: > > > On Mon, 26 Oct 2020 at 17:01, Geert Uytterhoeven <geert@...ux-m68k.org> wrote: > > > > On Mon, Oct 26, 2020 at 2:29 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote: > > > > > On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote: > > > > > > On Fri, Aug 21, 2020 at 9:56 PM Kees Cook <keescook@...omium.org> wrote: > > > > > > > In preparation for warning on orphan sections, discard > > > > > > > unwanted non-zero-sized generated sections, and enforce other > > > > > > > expected-to-be-zero-sized sections (since discarding them might hide > > > > > > > problems with them suddenly gaining unexpected entries). > > > > > > > > > > > > > > Suggested-by: Ard Biesheuvel <ardb@...nel.org> > > > > > > > Signed-off-by: Kees Cook <keescook@...omium.org> > > > > > > > > > > > > This is now commit be2881824ae9eb92 ("arm64/build: Assert for unwanted > > > > > > sections") in v5.10-rc1, and is causing the following error with > > > > > > renesas_defconfig[1]: > > > > > > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > > > > > I cannot reproduce this with the standard arm64 defconfig. > > > > > > > > > > > > I bisected the error to the aforementioned commit, but understand this > > > > > > is not the real reason. If I revert this commit, I still get: > > > > > > > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.got.plt' from > > > > > > `arch/arm64/kernel/head.o' being placed in section `.got.plt' > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.plt' from > > > > > > `arch/arm64/kernel/head.o' being placed in section `.plt' > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.data.rel.ro' from > > > > > > `arch/arm64/kernel/head.o' being placed in section `.data.rel.ro' > > > > > > aarch64-linux-gnu-ld: warning: orphan section `.eh_frame' from > > > > > > `kernel/bpf/core.o' being placed in section `.eh_frame' > > > > > > > > > > > > I.e. including the ".eh_frame" warning. I have tried bisecting that > > > > > > warning (i.e. with be2881824ae9eb92 reverted), but that leads me to > > > > > > commit b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section > > > > > > placement"), which is another red herring. > > > > > > > > > > kernel/bpf/core.o is the only file containing an eh_frame section, > > > > > causing the warning. > > When I see .eh_frame, I think -fno-asynchronous-unwind-tables is > missing from someone's KBUILD_CFLAGS. > But I don't see anything curious in kernel/bpf/Makefile, unless > cc-disable-warning is somehow broken. I tracked it down to kernel/bpf/core.c:___bpf_prog_run() being tagged with __no_fgcse aka __attribute__((optimize("-fno-gcse"))). Even if the function is trivially empty ("return 0;"), a ".eh_frame" section is generated. Removing the __no_fgcse tag fixes that. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
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