linux-kernel - Re: Problems compiling with KCFLAGS="-frecord-gcc-switches"

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Message-ID: <20170929203843.GA6611@roeck-us.net>
Date:   Fri, 29 Sep 2017 13:38:43 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: Problems compiling with KCFLAGS="-frecord-gcc-switches"

On Fri, Sep 29, 2017 at 01:00:56PM -0700, Guenter Roeck wrote:
> Hi Josh,
> 
> when trying to compile an image with KCFLAGS="-frecord-gcc-switches",
> I get the folllowing build warning/error.
> 
> make allmodconfig
> KCFLAGS="-frecord-gcc-switches" make arch/x86/kvm/emulate.o
> ./tools/objtool/objtool check --no-unreachable "arch/x86/kvm/emulate.o"
> 
> arch/x86/kvm/emulate.o: warning:
> 	objtool: .GCC.command.line+0x0: special: can't find new instruction
> 
> Building a full image aborts with:
> 
> WARNING: arch/x86/kvm/kvm.o(__ex_table+0x4c): Section mismatch in reference
> 	from the (unknown reference) (unknown)
> 	to the variable .GCC.command.line:kvm_fastop_exception
> FATAL: The relocation at __ex_table+0x4c references
> section ".GCC.command.line" which is not executable, IOW
> the kernel will fault if it ever tries to
> jump to it.  Something is seriously wrong
> and should be fixed.
> make[2]: *** [arch/x86/kvm/kvm.o] Error 1
> 
> Any idea what might cause this problem ?
> 

Here is another interesting problem, seen when building arm64 allmodconfig
-CONFIG_CPU_BIG_ENDIAN +CONFIG_EFI.

kallsyms failure:
	relative symbol value 0xffffff9008073000 out of range in relative mode

This is due to symbols such as

000000000000000e n __efistub_$d

in the symbol table. Those are not filtered out by kallsyms, resulting in a
relative "base" address of 0x0e, and all other symbols are out of range.
Those symbols are only generated in efi/libstubs.

Any idea what might be going on there, and how to fix it ?
An easy fix would be something like

-       else if (stype == 'N')
+       else if (toupper(stype) == 'N')

in kallsyms, but that doesn't seem like a clean solution to me.

Thanks,
Guenter