linux-kernel - Re: [PATCH] symbol : Make the size of the compile-related array fixed

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Date:   Fri, 16 Apr 2021 16:19:24 +1000
From:   Daniel Axtens <dja@...ens.net>
To:     韩大鹏(Han Dapeng) <handapeng@...o.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "x86\@kernel.org" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Mike Rapoport <rppt@...nel.org>,
        Pekka Enberg <penberg@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arseny Solokha <asolokha@...kras.ru>,
        韩大鹏(Han Dapeng) <handapeng@...o.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Kees Cook <keescook@...omium.org>,
        Joerg Roedel <jroedel@...e.de>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        "linuxppc-dev\@lists.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-s390\@vger.kernel.org" <linux-s390@...r.kernel.org>,
        "linux-kbuild\@vger.kernel.org" <linux-kbuild@...r.kernel.org>
Cc:     陈安庆(Anqing) <chenanqing@...o.com>
Subject: Re: [PATCH] symbol : Make the size of the compile-related array fixed

Hi,

Thanks for your contribution to the kernel!

I notice that your patch is sumbitted as an attachment. In future,
please could you submit your patch inline, rather than as an attachment?
See https://www.kernel.org/doc/html/v4.15/process/5.Posting.html
I'd recommend you use git send-email if possible: see e.g.
https://www.kernel.org/doc/html/v4.15/process/email-clients.html

> Subject: [PATCH] symbol : Make the size of the compile-related array fixed
>
> For the same code, the machine's user name, hostname, or compilation time
> may cause the kernel symbol address to be inconsistent, which is not
> friendly to some symbol-dependent software, such as Crash.

If I understand correctly, this patch makes it easier to recompile the
kernel from the same source but at a different time or on a different
machine or with a different user, but still get the same symbols.
Is that right?

I wonder if there are other reproducible build techniques that might be
simpler to apply? There is a kernel documentation page at
https://www.kernel.org/doc/html/latest/kbuild/reproducible-builds.html
which gives exisiting techniques to override the date, user and host.
Would they be sufficient to address your use case?

Kind regards,
Daniel

>
> Signed-off-by: Han Dapeng <handapeng@...o.com>
> ---
>  arch/powerpc/mm/nohash/kaslr_booke.c | 2 +-
>  arch/s390/boot/version.c             | 2 +-
>  arch/x86/boot/compressed/kaslr.c     | 2 +-
>  arch/x86/boot/version.c              | 2 +-
>  init/version.c                       | 4 ++--
>  scripts/mkcompile_h                  | 2 ++
>  6 files changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/arch/powerpc/mm/nohash/kaslr_booke.c b/arch/powerpc/mm/nohash/kaslr_booke.c
> index 4c74e8a5482b..494ef408e60c 100644
> --- a/arch/powerpc/mm/nohash/kaslr_booke.c
> +++ b/arch/powerpc/mm/nohash/kaslr_booke.c
> @@ -37,7 +37,7 @@ struct regions {
>  };
>  
>  /* Simplified build-specific string for starting entropy. */
> -static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
> +static const char build_str[COMPILE_STR_MAX] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
>  		LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;
>  
>  struct regions __initdata regions;
> diff --git a/arch/s390/boot/version.c b/arch/s390/boot/version.c
> index d32e58bdda6a..627416a27d74 100644
> --- a/arch/s390/boot/version.c
> +++ b/arch/s390/boot/version.c
> @@ -3,5 +3,5 @@
>  #include <generated/compile.h>
>  #include "boot.h"
>  
> -const char kernel_version[] = UTS_RELEASE
> +const char kernel_version[COMPILE_STR_MAX] = UTS_RELEASE
>  	" (" LINUX_COMPILE_BY "@" LINUX_COMPILE_HOST ") " UTS_VERSION;
> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> index b92fffbe761f..7b72b518a4c8 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -43,7 +43,7 @@
>  extern unsigned long get_cmd_line_ptr(void);
>  
>  /* Simplified build-specific string for starting entropy. */
> -static const char build_str[] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
> +static const char build_str[COMPILE_STR_MAX] = UTS_RELEASE " (" LINUX_COMPILE_BY "@"
>  		LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION;
>  
>  static unsigned long rotate_xor(unsigned long hash, const void *area,
> diff --git a/arch/x86/boot/version.c b/arch/x86/boot/version.c
> index a1aaaf6c06a6..08feaa2d7a10 100644
> --- a/arch/x86/boot/version.c
> +++ b/arch/x86/boot/version.c
> @@ -14,6 +14,6 @@
>  #include <generated/utsrelease.h>
>  #include <generated/compile.h>
>  
> -const char kernel_version[] =
> +const char kernel_version[COMPILE_STR_MAX] =
>  	UTS_RELEASE " (" LINUX_COMPILE_BY "@" LINUX_COMPILE_HOST ") "
>  	UTS_VERSION;
> diff --git a/init/version.c b/init/version.c
> index 92afc782b043..adfc9e91b56b 100644
> --- a/init/version.c
> +++ b/init/version.c
> @@ -35,11 +35,11 @@ struct uts_namespace init_uts_ns = {
>  EXPORT_SYMBOL_GPL(init_uts_ns);
>  
>  /* FIXED STRINGS! Don't touch! */
> -const char linux_banner[] =
> +const char linux_banner[COMPILE_STR_MAX] =
>  	"Linux version " UTS_RELEASE " (" LINUX_COMPILE_BY "@"
>  	LINUX_COMPILE_HOST ") (" LINUX_COMPILER ") " UTS_VERSION "\n";
>  
> -const char linux_proc_banner[] =
> +const char linux_proc_banner[COMPILE_STR_MAX] =
>  	"%s version %s"
>  	" (" LINUX_COMPILE_BY "@" LINUX_COMPILE_HOST ")"
>  	" (" LINUX_COMPILER ") %s\n";
> diff --git a/scripts/mkcompile_h b/scripts/mkcompile_h
> index 4ae735039daf..02b9d9d54da9 100755
> --- a/scripts/mkcompile_h
> +++ b/scripts/mkcompile_h
> @@ -65,6 +65,8 @@ UTS_VERSION="$(echo $UTS_VERSION $CONFIG_FLAGS $TIMESTAMP | cut -b -$UTS_LEN)"
>    LD_VERSION=$($LD -v | head -n1 | sed 's/(compatible with [^)]*)//' \
>  		      | sed 's/[[:space:]]*$//')
>    printf '#define LINUX_COMPILER "%s"\n' "$CC_VERSION, $LD_VERSION"
> +
> +  echo \#define COMPILE_STR_MAX 512
>  } > .tmpcompile
>  
>  # Only replace the real compile.h if the new one is different,
> -- 
> 2.27.0