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Message-ID: <20240811215226.GK10433@brightrain.aerifal.cx>
Date: Sun, 11 Aug 2024 17:52:29 -0400
From: Rich Felker <dalias@...c.org>
To: J. Neuschäfer <j.neuschaefer@....net>
Cc: lvm-devel@...ts.linux.dev, buildroot@...ldroot.org,
musl@...ts.openwall.com
Subject: Re: [PATCH lvm2] acinclude.m4: Link when trying CCFLAGS
On Sun, Aug 11, 2024 at 11:04:38AM +0200, J. Neuschäfer wrote:
> Through a build failure of LVM2 on musl-libc 1.2.5 in the Buildroot
> autobuild service[1], I noticed that musl-libc's Scrt1 for microblaze
> produces a relocation targeting the .text section, which subsequently
> leads to a crash at run-time because musl-libc does not support
> textrels[2]. Buildroot uses the "-z text" linker option to catch
> textrels early, on musl-libc.
>
> The error can be reduced to the following test case:
>
> $ cat hello.c
> #include <stdio.h>
> int main(void) { puts("Hello world!"); return 0; }
> $ host/bin/microblaze-buildroot-linux-musl-gcc hello.c -z text -pie -fPIC
> microblaze-buildroot-linux-musl/bin/ld: microblaze-buildroot-linux-musl/sysroot/lib/Scrt1.o:
> warning: relocation against `_start_c' in read-only section `.text'
> microblaze-buildroot-linux-musl/bin/ld: read-only segment has dynamic relocations
> collect2: error: ld returned 1 exit status
>
> LVM2 uses -pie only after the AC_TRY_CCFLAG macro has determined that it
> can be used. This is where the problem begins: AC_TRY_CCFLAG only tries
> compiling, it does not try linking the resulting object file.
>
> To catch problems like this, this patch changes AC_TRY_CCFLAG to link in
> addition to compiling. By detecting correctly that -pie does not work on
> musl-libc/microblaze with -ztext, the build failure in Buildroot is fixed.
>
> [1]: http://autobuild.buildroot.net/results/dc4/dc4fc33eaeafe5d6707d26a373560402533954f6/build-end.log
> [2]: https://www.openwall.com/lists/musl/2020/09/25/4
>
> Signed-off-by: J. Neuschäfer <j.neuschaefer@....net>
> ---
> Hi, I'm cross-posting this to the LVM2, Buildroot, and musl mailing
> lists to get potential feedback early on.
> ---
> acinclude.m4 | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/acinclude.m4 b/acinclude.m4
> index 47fdd59c3..9b1d3a605 100644
> --- a/acinclude.m4
> +++ b/acinclude.m4
> @@ -25,7 +25,7 @@ AC_DEFUN([AC_TRY_CCFLAG],
> ac_save_CFLAGS=$CFLAGS
> CFLAGS=$1
> AC_CACHE_CHECK([whether $CC accepts $1 flag], [ac_cv_flag_$2],
> - [AC_COMPILE_IFELSE([AC_LANG_PROGRAM()],
> + [AC_LINK_IFELSE([AC_LANG_PROGRAM()],
> [AS_VAR_SET([ac_cv_flag_$2], [yes])],
> [AS_VAR_SET([ac_cv_flag_$2], [no])])])
> CFLAGS=$ac_save_CFLAGS
>
> ---
No objection, but this is a bug in the tooling (ld) that we could also
avoid on the musl side. So there are probably 3 places things should
be changed here.
Rich
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