On Fri, Mar 24, 2023 at 8:33 PM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: > > (cc BTF list and maintainer) > > On Thu, 23 Mar 2023 at 22:12, Aurelien Jarno <aurelien@xxxxxxxxxxx> wrote: > > > > Hi, > > > > On 2023-03-22 15:51, Ard Biesheuvel wrote: > > > On Tue, 21 Mar 2023 at 23:26, Aurelien Jarno <aurelien@xxxxxxxxxxx> wrote: > > > > > > > > Hi, > > > > > > > > On 2022-10-13 08:35, Masahiro Yamada wrote: > > > > > In the previous discussion (see the Link tag), Ard pointed out that > > > > > arm/arm64/kernel/head.o does not need any special treatment - the only > > > > > piece that must appear right at the start of the binary image is the > > > > > image header which is emitted into .head.text. > > > > > > > > > > The linker script does the right thing to do. The build system does > > > > > not need to manipulate the link order of head.o. > > > > > > > > > > Link: https://lore.kernel.org/lkml/CAMj1kXH77Ja8bSsq2Qj8Ck9iSZKw=1F8Uy-uAWGVDm4-CG=EuA@xxxxxxxxxxxxxx/ > > > > > Suggested-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > > > > > Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx> > > > > > --- > > > > > > > > > > scripts/head-object-list.txt | 1 - > > > > > 1 file changed, 1 deletion(-) > > > > > > > > > > diff --git a/scripts/head-object-list.txt b/scripts/head-object-list.txt > > > > > index b16326a92c45..f226e45e3b7b 100644 > > > > > --- a/scripts/head-object-list.txt > > > > > +++ b/scripts/head-object-list.txt > > > > > @@ -15,7 +15,6 @@ arch/alpha/kernel/head.o > > > > > arch/arc/kernel/head.o > > > > > arch/arm/kernel/head-nommu.o > > > > > arch/arm/kernel/head.o > > > > > -arch/arm64/kernel/head.o > > > > > arch/csky/kernel/head.o > > > > > arch/hexagon/kernel/head.o > > > > > arch/ia64/kernel/head.o > > > > > > > > This patch causes a significant increase of the arch/arm64/boot/Image > > > > size. For instance the generic arm64 Debian kernel went from 31 to 39 MB > > > > after this patch has been applied to the 6.1 stable tree. > > > > > > > > In turn this causes issues with some bootloaders, for instance U-Boot on > > > > a Raspberry Pi limits the kernel size to 36 MB. > > > > > > > > > > I cannot reproduce this with mainline > > > > > > With the patch > > > > > > $ size vmlinux > > > text data bss dec hex filename > > > 24567309 14752630 621680 39941619 26175f3 vmlinux > > > > > > With the patch reverted > > > > > > $ size vmlinux > > > text data bss dec hex filename > > > 24567309 14752694 621680 39941683 2617633 vmlinux > > > > I have tried with the current mainline, this is what I get, using GCC 12.2.0 > > and binutils 2.40: > > > > text data bss dec hex filename > > 32531655 8192996 621968 41346619 276e63b vmlinux.orig > > 25170610 8192996 621968 33985574 2069426 vmlinux.revert > > > > > It would help to compare the resulting vmlinux ELF images from both > > > builds to see where the extra space is being allocated > > > > At a first glance, it seems the extra space is allocated in the BTF > > section. I have uploaded the resulting files as well as the config file > > I used there: > > https://temp.aurel32.net/linux-arm64-size-head.o.tar.gz > > > > Indeed. So we go from > > [15] .BTF PROGBITS ffff8000091d1ff4 011e1ff4 > 00000000005093d6 0000000000000000 A 0 0 1 > > to > > [15] .BTF PROGBITS ffff8000091d1ff4 011e1ff4 > 0000000000c0e5eb 0000000000000000 A 0 0 1 > > i.e, from 5 MiB to 12+ MiB of BTF metadata. > > To me, it is not clear at all how one would be related to the other, > so it will leave it to the Kbuild and BTF experts to chew on this one. Strange. I used the .config file Aurelien provided, but I still cannot reproduce this issue. The vmlinux size is small as-is in the current mainline. [mainline] masahiro@zoe:~/ref/linux(master)$ git log --oneline -1 65aca32efdcb (HEAD -> master, origin/master, origin/HEAD) Merge tag 'mm-hotfixes-stable-2023-03-24-17-09' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm masahiro@zoe:~/ref/linux(master)$ aarch64-linux-gnu-size vmlinux text data bss dec hex filename 24561282 8186912 622032 33370226 1fd3072 vmlinux masahiro@zoe:~/ref/linux(master)$ aarch64-linux-gnu-readelf -S vmlinux | grep -A1 BTF [15] .BTF PROGBITS ffff8000091c0708 011d0708 000000000048209c 0000000000000000 A 0 0 1 [16] .BTF_ids PROGBITS ffff8000096427a4 016527a4 0000000000000a1c 0000000000000000 A 0 0 1 [mainline + revert 994b7ac] masahiro@zoe:~/ref/linux2(testing)$ git log --oneline -2 856c80dd789c (HEAD -> testing) Revert "arm64: remove special treatment for the link order of head.o" 65aca32efdcb (origin/master, origin/HEAD, master) Merge tag 'mm-hotfixes-stable-2023-03-24-17-09' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm masahiro@zoe:~/ref/linux2(testing)$ aarch64-linux-gnu-size vmlinux text data bss dec hex filename 24561329 8186912 622032 33370273 1fd30a1 vmlinux masahiro@zoe:~/ref/linux2(testing)$ aarch64-linux-gnu-readelf -S vmlinux | grep -A1 BTF [15] .BTF PROGBITS ffff8000091c0708 011d0708 00000000004820cb 0000000000000000 A 0 0 1 [16] .BTF_ids PROGBITS ffff8000096427d4 016527d4 0000000000000a1c 0000000000000000 A 0 0 1 I still do not know what affects reproducibility. (compiler version, pahole version, etc. ?) Aurelien used GCC 12 + binutils 2.40, but my toolchain is a bit older. FWIW, I tested this on Ubuntu 22.04LTS. masahiro@zoe:~/ref/linux(master)$ aarch64-linux-gnu-gcc --version aarch64-linux-gnu-gcc (Ubuntu 11.3.0-1ubuntu1~22.04) 11.3.0 Copyright (C) 2021 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. masahiro@zoe:~/ref/linux(master)$ pahole --version v1.22 masahiro@zoe:~/ref/linux(master)$ aarch64-linux-gnu-as --version GNU assembler (GNU Binutils for Ubuntu) 2.38 Copyright (C) 2022 Free Software Foundation, Inc. This program is free software; you may redistribute it under the terms of the GNU General Public License version 3 or later. This program has absolutely no warranty. This assembler was configured for a target of `aarch64-linux-gnu'. -- Best Regards Masahiro Yamada
