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From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Mon, 22 May 2017 07:39:57 -0700
Message-ID: <CAMe9rOramET+aLnFyzLHB7SPDpcpssEPQmG=e0Y4kb8QuPhKyA@mail.gmail.com>
Subject: Re: [PATCH 7/7] DWARF: add the config option
To: Jiri Kosina <jikos@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Jiri Slaby <jslaby@suse.cz>, Andrew Morton <akpm@linux-foundation.org>,
        live-patching@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
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On Mon, May 22, 2017 at 4:34 AM, Jiri Kosina <jikos@kernel.org> wrote:
> On Sat, 20 May 2017, H.J. Lu wrote:
>
>> >>>> pushq %whatever
>> >>>> .cfi_adjust_sp -8
>> >>>> ...
>> >>>> popq %whatever
>> >>>> .cfi_adjust_sp 8
>> >>>>
>> >>
>> >> Np.  Compiler needs to generate this.
>> >>
>> >
>> > How would the compiler generate this when inline asm is involved?  For
>> > the kernel, objtool could get around the need to have these
>> > annotations, but not so much for user code?  Is the compiler supposed
>> > to parse the inline asm?  Would the compiler provide some magic % code
>> > to represent the current CFA base register?
>>
>> Here is one example of inline asm with call frame info:
>>
>> https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/x86_64/sigaction.c;h=be058bac436d1cc9794b2b03107676ed99f6b872;hb=HEAD
>
> That brings us basically pretty close to square one though; having to
> maintain "manual" anotations. Something we're pretty much trying to avoid
> through this excercise.

Assembler only encodes instructions.  You need to a different tool
to figure out what an instruction does.


-- 
H.J.