linux-kernel - Re: [PATCH] kbuild: mkcompile_h: Include $LD version in /proc/version

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Date:   Wed, 8 Apr 2020 12:22:33 +0200
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kbuild@...r.kernel.org,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kbuild: mkcompile_h: Include $LD version in /proc/version

On Thu, Apr 2, 2020 at 10:18 AM Kees Cook <keescook@...omium.org> wrote:
>
> When doing Clang builds of the kernel, it is possible to link with
> either ld.bfd (binutils) or ld.lld (LLVM), but it is not possible to
> discover this from a running kernel. Add the "$LD -v" output to
> /proc/version.
>

What about also having the linker and its version in the generated
linux-config file?

$ git diff
diff --git a/Kconfig b/Kconfig
index e10b3ee084d4..98fd210786e5 100644
--- a/Kconfig
+++ b/Kconfig
@@ -5,7 +5,7 @@
 #
 mainmenu "Linux/$(ARCH) $(KERNELVERSION) Kernel Configuration"

-comment "Compiler: $(CC_VERSION_TEXT)"
+comment "Compiler: $(CC_VERSION_TEXT) Linker: $(LD_VERSION_TEXT)"

 source "scripts/Kconfig.include"

diff --git a/Makefile b/Makefile
index 91b90ec1737c..42d6834b2255 100644
--- a/Makefile
+++ b/Makefile
@@ -553,6 +553,9 @@ endif
 # and from include/config/auto.conf.cmd to detect the compiler upgrade.
 CC_VERSION_TEXT = $(shell $(CC) --version 2>/dev/null | head -n 1)

+# LD_VERSION_TEXT is referenced from Kconfig (so it needs export).
+LD_VERSION_TEXT = $(shell $(LD) --version 2>/dev/null | head -n 1)
+
 ifdef config-build
 # ===========================================================================
 # *config targets only - make sure prerequisites are updated, and descend
@@ -562,7 +565,7 @@ ifdef config-build
 # KBUILD_DEFCONFIG may point out an alternative default configuration
 # used for 'make defconfig'
 include arch/$(SRCARCH)/Makefile
-export KBUILD_DEFCONFIG KBUILD_KCONFIG CC_VERSION_TEXT
+export KBUILD_DEFCONFIG KBUILD_KCONFIG CC_VERSION_TEXT LD_VERSION_TEXT

 config: outputmakefile scripts_basic FORCE
        $(Q)$(MAKE) $(build)=scripts/kconfig $@

This generates here:

--- /boot/config-5.6.0-3-amd64-clang    2020-04-01 13:18:13.000000000 +0200
+++ .config     2020-04-08 12:16:43.477674201 +0200
@@ -1,10 +1,10 @@
 #
 # Automatically generated file; DO NOT EDIT.
-# Linux/x86 5.6.0 Kernel Configuration
+# Linux/x86 5.6.3 Kernel Configuration
 #

 #
-# Compiler: clang version 10.0.0-1
+# Compiler: clang version 10.0.0-2  Linker: LLD 10.0.0 (compatible
with GNU linkers)

- Sedat -