Re: [PATCH v2] arch: fix broken BuildID for arm64 and riscv

[Nathan Chancellor]

Hi Masahiro,

On Tue, Dec 27, 2022 at 03:45:37AM +0900, Masahiro Yamada wrote:
> Dennis Gilmore reports that the BuildID is missing in the arm64 vmlinux
> since commit 994b7ac1697b ("arm64: remove special treatment for the
> link order of head.o").
> 
> The issue is that the type of .notes section, which contains the BuildID,
> changed from NOTES to PROGBITS.
> 
> Ard Biesheuvel figured out that whichever object gets linked first gets
> to decide the type of a section. The PROGBITS type is the result of the
> compiler emitting .note.GNU-stack as PROGBITS rather than NOTE.
> 
> While Ard provided a fix for arm64, I want to fix this globally because
> the same issue is happening on riscv since commit 2348e6bf4421 ("riscv:
> remove special treatment for the link order of head.o"). This problem
> will happen in general for other architectures if they start to drop
> unneeded entries from scripts/head-object-list.txt.
> 
> Discard .note.GNU-stack in include/asm-generic/vmlinux.lds.h.
> 
> Link: https://lore.kernel.org/lkml/CAABkxwuQoz1CTbyb57n0ZX65eSYiTonFCU8-LCQc=74D=xE=rA@xxxxxxxxxxxxxx/
> Fixes: 994b7ac1697b ("arm64: remove special treatment for the link order of head.o")
> Fixes: 2348e6bf4421 ("riscv: remove special treatment for the link order of head.o")
> Reported-by: Dennis Gilmore <dennis@xxxxxxxx>
> Suggested-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> ---
> 
> Changes in v2:
>   - discard .note.GNU-stack before .notes because many architectures
>     call DISCARDS at the end of their linker scripts
> 
>  include/asm-generic/vmlinux.lds.h | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index a94219e9916f..659bf3b31c91 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -891,7 +891,12 @@
>  #define PRINTK_INDEX
>  #endif
>  
> +/*
> + * Discard .note.GNU-stack, which is emitted as PROGBITS by the compiler.
> + * Otherwise, the type of .notes section would become PROGBITS instead of NOTES.
> + */
>  #define NOTES								\
> +	/DISCARD/ : { *(.note.GNU-stack) }				\
>  	.notes : AT(ADDR(.notes) - LOAD_OFFSET) {			\
>  		BOUNDED_SECTION_BY(.note.*, _notes)			\
>  	} NOTES_HEADERS							\
> -- 
> 2.34.1
> 
> 

I just bisected this change as the cause of a few link failures that we
now see in CI with Debian's binutils (2.35.2):

https://storage.tuxsuite.com/public/clangbuiltlinux/continuous-integration2/builds/2Jjl88DXc3YRi2RtvXAzlS8NQ4p/build.log

This does not appear to be related to clang/LLVM because I can easily
reproduce it with Debian's s390x GCC and binutils building defconfig:

$ s390x-linux-gnu-gcc --version | head -1
s390x-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110

$ s390x-linux-gnu-ld --version | head -1
GNU ld (GNU Binutils for Debian) 2.35.2

$ make -skj"$(nproc)" ARCH=s390 CROSS_COMPILE=s390x-linux-gnu- O=build mrproper defconfig all
...
`.exit.text' referenced in section `.s390_return_reg' of fs/jbd2/journal.o: defined in discarded section `.exit.text' of fs/jbd2/journal.o
`.exit.text' referenced in section `__jump_table' of fs/fuse/inode.o: defined in discarded section `.exit.text' of fs/fuse/inode.o
`.exit.text' referenced in section `__jump_table' of fs/fuse/inode.o: defined in discarded section `.exit.text' of fs/fuse/inode.o
`.exit.text' referenced in section `.s390_indirect_call' of fs/btrfs/super.o: defined in discarded section `.exit.text' of fs/btrfs/super.o
`.exit.text' referenced in section `.s390_return_mem' of fs/btrfs/super.o: defined in discarded section `.exit.text' of fs/btrfs/super.o
`.exit.text' referenced in section `.s390_return_mem' of fs/btrfs/volumes.o: defined in discarded section `.exit.text' of fs/btrfs/volumes.o
`.exit.text' referenced in section `.s390_return_mem' of fs/btrfs/volumes.o: defined in discarded section `.exit.text' of fs/btrfs/volumes.o
`.exit.text' referenced in section `__bug_table' of crypto/algboss.o: defined in discarded section `.exit.text' of crypto/algboss.o
`.exit.text' referenced in section `.s390_return_mem' of crypto/algboss.o: defined in discarded section `.exit.text' of crypto/algboss.o
`.exit.text' referenced in section `.s390_return_reg' of crypto/xor.o: defined in discarded section `.exit.text' of crypto/xor.o
`.exit.text' referenced in section `.s390_return_reg' of lib/atomic64_test.o: defined in discarded section `.exit.text' of lib/atomic64_test.o
`.exit.text' referenced in section `.s390_return_mem' of drivers/char/tpm/tpm-dev-common.o: defined in discarded section `.exit.text' of drivers/char/tpm/tpm-dev-common.o
`.exit.text' referenced in section `.s390_return_mem' of drivers/char/tpm/tpm-dev-common.o: defined in discarded section `.exit.text' of drivers/char/tpm/tpm-dev-common.o
`.exit.text' referenced in section `.s390_return_mem' of drivers/scsi/sd.o: defined in discarded section `.exit.text' of drivers/scsi/sd.o
`.exit.text' referenced in section `.altinstructions' of drivers/md/md.o: defined in discarded section `.exit.text' of drivers/md/md.o
`.exit.text' referenced in section `.altinstructions' of drivers/md/md.o: defined in discarded section `.exit.text' of drivers/md/md.o
`.exit.text' referenced in section `.s390_indirect_call' of drivers/md/dm.o: defined in discarded section `.exit.text' of drivers/md/dm.o
`.exit.text' referenced in section `.s390_return_reg' of net/802/psnap.o: defined in discarded section `.exit.text' of net/802/psnap.o
`.exit.text' referenced in section `.altinstructions' of net/iucv/iucv.o: defined in discarded section `.exit.text' of net/iucv/iucv.o
`.exit.text' referenced in section `__bug_table' of drivers/s390/cio/qdio_thinint.o: defined in discarded section `.exit.text' of drivers/s390/cio/qdio_thinint.o
`.exit.text' referenced in section `.s390_return_mem' of drivers/s390/block/dasd_diag.o: defined in discarded section `.exit.text' of drivers/s390/block/dasd_diag.o
`.exit.text' referenced in section `.s390_return_mem' of drivers/s390/char/tty3270.o: defined in discarded section `.exit.text' of drivers/s390/char/tty3270.o
`.exit.text' referenced in section `__bug_table' of drivers/s390/net/qeth_l3_main.o: defined in discarded section `.exit.text' of drivers/s390/net/qeth_l3_main.o
`.exit.text' referenced in section `__bug_table' of drivers/s390/net/qeth_l3_main.o: defined in discarded section `.exit.text' of drivers/s390/net/qeth_l3_main.o
s390x-linux-gnu-ld: BFD (GNU Binutils for Debian) 2.35.2 assertion fail ../../bfd/elf64-s390.c:3349
...

I ended up bisecting binutils for the fix, as I could not reproduce it
with 2.36+. My bisect landed on commit 21401fc7bf6 ("Duplicate output
sections in scripts"):

https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=21401fc7bf67dbf73f4a3eda4bcfc58fa4211584

Unfortunately, I cannot immediately grok why this commit cause the above
issue nor why the binutils commit resolves it so I figured I would
immediately report it for public investigation's sake and quicker
resolution.

Cheers,
Nathan