linux-kernel - Re: [PATCH] x86/boot/compressed: Fix compressed kernel linking with lld

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Message-ID: <20200222185806.ywnqhfqmy67akfsa@google.com>
Date:   Sat, 22 Feb 2020 10:58:06 -0800
From:   Fangrui Song <maskray@...gle.com>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Borislav Petkov <bp@...en8.de>,
        Nathan Chancellor <natechancellor@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        Michael Matz <matz@...e.de>
Subject: Re: [PATCH] x86/boot/compressed: Fix compressed kernel linking with
 lld

On 2020-02-22, Nathan Chancellor wrote:
>On Sat, Feb 22, 2020 at 12:18:59PM -0500, Arvind Sankar wrote:
>> Commit TBD ("x86/boot/compressed: Remove unnecessary sections from
>> bzImage") discarded unnecessary sections with *(*). While this works
>> fine with the bfd linker, lld tries to also discard essential sections
>> like .shstrtab, .symtab and .strtab, which results in the link failing
>> since .shstrtab is required by the ELF specification. .symtab and
>> .strtab are also necessary to generate the zoffset.h file for the
>> bzImage header.
>>
>> Since the only sizeable section that can be discarded is .eh_frame,
>> restrict the discard to only .eh_frame to be safe.
>>
>> Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>
>> ---
>> Sending as a fix on top of tip/x86/boot.
>>
>>  arch/x86/boot/compressed/vmlinux.lds.S | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
>> index 12a20603d92e..469dcf800a2c 100644
>> --- a/arch/x86/boot/compressed/vmlinux.lds.S
>> +++ b/arch/x86/boot/compressed/vmlinux.lds.S
>> @@ -74,8 +74,8 @@ SECTIONS
>>  	. = ALIGN(PAGE_SIZE);	/* keep ZO size page aligned */
>>  	_end = .;
>>
>> -	/* Discard all remaining sections */
>> +	/* Discard .eh_frame to save some space */
>>  	/DISCARD/ : {
>> -		*(*)
>> +		*(.eh_frame)
>>  	}
>>  }
>> --
>> 2.24.1
>>
>
>FWIW:
>
>Tested-by: Nathan Chancellor <natechancellor@...il.com>

I am puzzled. Doesn't -fno-asynchronous-unwind-tables suppress
.eh_frame in the object files? Why are there still .eh_frame?

Though, there is prior art: arch/s390/boot/compressed/vmlinux.lds.S also discards .eh_frame