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Mon, 26 Oct 2020 10:43:59 -0700 (PDT) MIME-Version: 1.0 References: <20200821194310.3089815-1-keescook@chromium.org> <20200821194310.3089815-14-keescook@chromium.org> In-Reply-To: From: Geert Uytterhoeven Date: Mon, 26 Oct 2020 18:43:48 +0100 Message-ID: Subject: Re: [PATCH v6 13/29] arm64/build: Assert for unwanted sections To: Ard Biesheuvel X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201026_134400_238214_51E9ADD0 X-CRM114-Status: GOOD ( 30.16 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Linux-Arch , linux-efi , Kees Cook , Arnd Bergmann , Catalin Marinas , Masahiro Yamada , the arch/x86 maintainers , Nick Desaulniers , Russell King , Linux Kernel Mailing List , Linux-Renesas , clang-built-linux , Arvind Sankar , Ingo Molnar , James Morse , Nathan Chancellor , Borislav Petkov , Peter Collingbourne , Ingo Molnar , Linux ARM Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Ard, On Mon, Oct 26, 2020 at 6:39 PM Ard Biesheuvel wrote: > On Mon, 26 Oct 2020 at 17:01, Geert Uytterhoeven wrote: > > On Mon, Oct 26, 2020 at 2:29 PM Geert Uytterhoeven wrote: > > > On Mon, Oct 26, 2020 at 1:29 PM Geert Uytterhoeven wrote: > > > > On Fri, Aug 21, 2020 at 9:56 PM Kees Cook 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 > > > > > Signed-off-by: Kees Cook > > > > > > > > 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. > > > If I compile core.c with "-g" added, like arm64 defconfig does, the > > > eh_frame section is no longer emitted. > > > > > > Hence setting CONFIG_DEBUG_INFO=y, cfr. arm64 defconfig, the warning > > > is gone, but I'm back to the the "Unexpected GOT/PLT entries" below... > > > > > > > Note that even on plain be2881824ae9eb92, I get: > > > > > > > > aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected! > > > > aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected! > > > > > > > > The parent commit obviously doesn't show that (but probably still has > > > > the problem). > > > > Reverting both > > b3e5d80d0c48c0cc ("arm64/build: Warn on orphan section placement") > > be2881824ae9eb92 ("arm64/build: Assert for unwanted sections") > > seems to solve my problems, without any ill effects? > > > > I cannot reproduce the issue here with my distro GCC+binutils (Debian 8.3.0) > > The presence of .data.rel.ro and .got.plt sections suggests that the > toolchain is using -fpie and/or -z relro to build shared objects > rather than a fully linked bare metal binary. > > Which toolchain are you using? Does adding -fno-pie to the compiler gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04) from Ubuntu 20.04LTS. > command line and/or adding -z norelro to the linker command line make > any difference? I'll give that a try later... Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel