From: Fangrui Song <maskray@google.com>
To: Nathan Chancellor <natechancellor@gmail.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
Masahiro Yamada <masahiroy@kernel.org>,
linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org,
clang-built-linux@googlegroups.com, linux-kbuild@vger.kernel.org,
Nick Desaulniers <ndesaulniers@google.com>,
Sami Tolvanen <samitolvanen@google.com>,
Dmitry Golovin <dima@golovin.in>,
Sedat Dilek <sedat.dilek@gmail.com>
Subject: Re: [PATCH v4 4/5] MIPS: VDSO: Use $(LD) instead of $(CC) to link VDSO
Date: Tue, 28 Apr 2020 15:54:01 -0700 [thread overview]
Message-ID: <20200428225401.7yrld7u2xr67t4xf@google.com> (raw)
In-Reply-To: <20200428221419.2530697-5-natechancellor@gmail.com>
On 2020-04-28, Nathan Chancellor wrote:
>Currently, the VDSO is being linked through $(CC). This does not match
>how the rest of the kernel links objects, which is through the $(LD)
>variable.
>
>When clang is built in a default configuration, it first attempts to use
>the target triple's default linker then the system's default linker,
>unless told otherwise through -fuse-ld=... We do not use -fuse-ld=
>because it can be brittle and we have support for invoking $(LD)
>directly. See commit fe00e50b2db8c ("ARM: 8858/1: vdso: use $(LD)
>instead of $(CC) to link VDSO") and commit 691efbedc60d2 ("arm64: vdso:
>use $(LD) instead of $(CC) to link VDSO") for examples of doing this in
>the VDSO.
>
>Do the same thing here. Replace the custom linking logic with $(cmd_ld)
>and ldflags-y so that $(LD) is respected. We need to explicitly add two
>flags to the linker that were implicitly passed by the compiler:
>-G 0 (which comes from ccflags-vdso) and --eh-frame-hdr.
>
>Before this patch (generated by adding '-v' to VDSO_LDFLAGS):
>
><gcc_prefix>/libexec/gcc/mips64-linux/9.3.0/collect2 \
>-plugin <gcc_prefix>/libexec/gcc/mips64-linux/9.3.0/liblto_plugin.so \
>-plugin-opt=<gcc_prefix>/libexec/gcc/mips64-linux/9.3.0/lto-wrapper \
>-plugin-opt=-fresolution=/tmp/ccGEi5Ka.res \
>--eh-frame-hdr \
>-G 0 \
>-EB \
>-mips64r2 \
>-shared \
>-melf64btsmip \
>-o arch/mips/vdso/vdso.so.dbg.raw \
>-L<gcc_prefix>/lib/gcc/mips64-linux/9.3.0/64 \
>-L<gcc_prefix>/lib/gcc/mips64-linux/9.3.0 \
>-L<gcc_prefix>/lib/gcc/mips64-linux/9.3.0/../../../../mips64-linux/lib \
>-Bsymbolic \
>--no-undefined \
>-soname=linux-vdso.so.1 \
>-EB \
>--hash-style=sysv \
>--build-id \
>-T arch/mips/vdso/vdso.lds \
>arch/mips/vdso/elf.o \
>arch/mips/vdso/vgettimeofday.o \
>arch/mips/vdso/sigreturn.o
>
>After this patch:
>
><gcc_prefix>/bin/mips64-linux-ld \
>-m elf64btsmip \
>-Bsymbolic \
>--no-undefined \
>-soname=linux-vdso.so.1 \
>-EB \
>-nostdlib \
>-shared \
>-G 0 \
>--eh-frame-hdr \
>--hash-style=sysv \
>--build-id \
>-T arch/mips/vdso/vdso.lds \
>arch/mips/vdso/elf.o \
>arch/mips/vdso/vgettimeofday.o
>arch/mips/vdso/sigreturn.o \
>-o arch/mips/vdso/vdso.so.dbg.raw
>
>Note that we leave behind -mips64r2. Turns out that ld ignores it (see
>get_emulation in ld/ldmain.c). This is true of current trunk and 2.23,
>which is the minimum supported version for the kernel:
>
>https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=ld/ldmain.c;hb=aa4209e7b679afd74a3860ce25659e71cc4847d5#l593
>https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=ld/ldmain.c;hb=a55e30b51bc6227d8d41f707654d0a5620978dcf#l641
>
>Before this patch, LD=ld.lld did nothing:
>
>$ llvm-readelf -p.comment arch/mips/vdso/vdso.so.dbg | sed 's/(.*//'
>String dump of section '.comment':
>[ 0] ClangBuiltLinux clang version 11.0.0
>
>After this patch, it does:
>
>$ llvm-readelf -p.comment arch/mips/vdso/vdso.so.dbg | sed 's/(.*//'
>String dump of section '.comment':
>[ 0] Linker: LLD 11.0.0
>[ 62] ClangBuiltLinux clang version 11.0.0
>
>Link: https://github.com/ClangBuiltLinux/linux/issues/785
>Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
>---
>
>v3 -> v4:
>
>* Improve commit message to show that ld command is effectively the
> same as the one generated by GCC.
>
>* Add '-G 0' and '--eh-frame-hdr' because they were added by GCC.
My understanding is that we start to use more -fasynchronous-unwind-tables to eliminate .eh_frame in object files.
Without .eh_frame, LD --eh-frame-hdr is really not useful.
Sigh... -G 0. This is an option ignored by LLD. GCC devs probably should
have used the long option --gpsize rather than take the short option -G.
Even better, -z gpsize= or similar if this option is specific to ELF.
>v2 -> v3:
>
>* New patch.
>
> arch/mips/vdso/Makefile | 13 ++++---------
> 1 file changed, 4 insertions(+), 9 deletions(-)
>
>diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
>index 92b53d1df42c3..2e64c7600eead 100644
>--- a/arch/mips/vdso/Makefile
>+++ b/arch/mips/vdso/Makefile
>@@ -60,10 +60,9 @@ ifdef CONFIG_MIPS_DISABLE_VDSO
> endif
>
> # VDSO linker flags.
>-VDSO_LDFLAGS := \
>- -Wl,-Bsymbolic -Wl,--no-undefined -Wl,-soname=linux-vdso.so.1 \
>- $(addprefix -Wl$(comma),$(filter -E%,$(KBUILD_CFLAGS))) \
>- -nostdlib -shared -Wl,--hash-style=sysv -Wl,--build-id
>+ldflags-y := -Bsymbolic --no-undefined -soname=linux-vdso.so.1 \
>+ $(filter -E%,$(KBUILD_CFLAGS)) -nostdlib -shared \
>+ -G 0 --eh-frame-hdr --hash-style=sysv --build-id -T
>
> CFLAGS_REMOVE_vdso.o = -pg
>
>@@ -82,11 +81,7 @@ quiet_cmd_vdso_mips_check = VDSOCHK $@
> #
>
> quiet_cmd_vdsold_and_vdso_check = LD $@
>- cmd_vdsold_and_vdso_check = $(cmd_vdsold); $(cmd_vdso_check); $(cmd_vdso_mips_check)
>-
>-quiet_cmd_vdsold = VDSO $@
>- cmd_vdsold = $(CC) $(c_flags) $(VDSO_LDFLAGS) \
>- -Wl,-T $(filter %.lds,$^) $(filter %.o,$^) -o $@
>+ cmd_vdsold_and_vdso_check = $(cmd_ld); $(cmd_vdso_check); $(cmd_vdso_mips_check)
>
> quiet_cmd_vdsoas_o_S = AS $@
> cmd_vdsoas_o_S = $(CC) $(a_flags) -c -o $@ $<
>--
>2.26.2
>
next prev parent reply other threads:[~2020-04-28 22:54 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-19 18:04 [PATCH 1/2] kbuild: add CONFIG_LD_IS_LLD Nathan Chancellor
2020-04-19 18:04 ` [PATCH 2/2] MIPS: VDSO: Do not disable VDSO when linking with ld.lld Nathan Chancellor
2020-04-19 18:17 ` Nathan Chancellor
2020-04-19 19:32 ` Masahiro Yamada
2020-04-19 20:05 ` Nathan Chancellor
2020-04-19 20:21 ` [PATCH v2 1/3] kbuild: add CONFIG_LD_IS_LLD Nathan Chancellor
2020-04-19 20:21 ` [PATCH v2 2/3] MIPS: VDSO: Move disabling the VDSO logic to Kconfig Nathan Chancellor
2020-04-20 9:53 ` Sedat Dilek
2020-04-21 2:42 ` Nathan Chancellor
2020-04-23 14:41 ` Masahiro Yamada
2020-04-19 20:21 ` [PATCH v2 3/3] MIPS: VDSO: Allow ld.lld to link the VDSO Nathan Chancellor
2020-04-23 14:38 ` [PATCH v2 1/3] kbuild: add CONFIG_LD_IS_LLD Masahiro Yamada
2020-04-23 17:18 ` [PATCH v3 1/4] " Nathan Chancellor
2020-04-23 17:18 ` [PATCH v3 2/4] MIPS: VDSO: Move disabling the VDSO logic to Kconfig Nathan Chancellor
2020-04-23 17:18 ` [PATCH v3 3/4] MIPS: VDSO: Use $(LD) instead of $(CC) to link VDSO Nathan Chancellor
2020-04-26 16:27 ` Thomas Bogendoerfer
2020-04-27 2:08 ` Nathan Chancellor
2020-04-27 16:22 ` Maciej W. Rozycki
2020-04-27 23:24 ` Nathan Chancellor
2020-04-29 17:46 ` Maciej W. Rozycki
2020-04-30 3:14 ` Nathan Chancellor
2020-04-28 2:17 ` Nathan Chancellor
2020-04-23 17:18 ` [PATCH v3 4/4] MIPS: VDSO: Allow ld.lld to link the VDSO Nathan Chancellor
2020-04-28 22:14 ` [PATCH v5 0/5] Allow ld.lld to link the MIPS VDSO Nathan Chancellor
2020-04-28 22:14 ` [PATCH v4 1/5] kbuild: add CONFIG_LD_IS_LLD Nathan Chancellor
2020-04-29 7:13 ` Sedat Dilek
2020-04-30 3:05 ` Nathan Chancellor
2020-04-28 22:14 ` [PATCH v4 2/5] MIPS: VDSO: Move disabling the VDSO logic to Kconfig Nathan Chancellor
2020-04-28 22:14 ` [PATCH v4 3/5] MIPS: Unconditionally specify '-EB' or '-EL' Nathan Chancellor
2020-04-28 22:14 ` [PATCH v4 4/5] MIPS: VDSO: Use $(LD) instead of $(CC) to link VDSO Nathan Chancellor
2020-04-28 22:54 ` Fangrui Song [this message]
2020-04-29 0:44 ` Nathan Chancellor
2020-05-02 13:34 ` Maciej W. Rozycki
2020-05-02 13:50 ` Maciej W. Rozycki
2020-05-02 15:49 ` Nathan Chancellor
2020-04-28 22:14 ` [PATCH v4 5/5] MIPS: VDSO: Allow ld.lld to link the VDSO Nathan Chancellor
2020-04-29 7:04 ` [PATCH v5 0/5] Allow ld.lld to link the MIPS VDSO Sedat Dilek
2020-04-30 3:06 ` Nathan Chancellor
2020-05-12 8:05 ` Thomas Bogendoerfer
2020-05-12 8:28 ` Nathan Chancellor
2020-05-13 11:18 ` Thomas Bogendoerfer
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200428225401.7yrld7u2xr67t4xf@google.com \
--to=maskray@google.com \
--cc=clang-built-linux@googlegroups.com \
--cc=dima@golovin.in \
--cc=linux-kbuild@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mips@vger.kernel.org \
--cc=masahiroy@kernel.org \
--cc=natechancellor@gmail.com \
--cc=ndesaulniers@google.com \
--cc=samitolvanen@google.com \
--cc=sedat.dilek@gmail.com \
--cc=tsbogend@alpha.franken.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).