linux-kernel - Re: [PATCH 7/7] DWARF: add the config option

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Date:   Mon, 22 May 2017 07:39:57 -0700
From:   "H.J. Lu" <hjl.tools@...il.com>
To:     Jiri Kosina <jikos@...nel.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jiri Slaby <jslaby@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        live-patching@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 7/7] DWARF: add the config option

On Mon, May 22, 2017 at 4:34 AM, Jiri Kosina <jikos@...nel.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.