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

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Date:   Fri, 19 May 2017 13:57:24 -0700
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>, linux-kernel@...r.kernel.org
Cc:     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>,
        Andy Lutomirski <luto@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 7/7] DWARF: add the config option

On 05/19/17 13:53, Josh Poimboeuf wrote:
>>
>> One instance of the structure would exist for each time the stack
>> pointer changes, e.g. for every function entry, push/pop, and rsp
>> add/subtract.  The data could be assembled and sorted offline, possibly
>> derived from DWARF, or more likely, generated by objtool.  After doing
>> some rough calculations, I think the section size would be comparable to
>> the sizes of the DWARF .eh_frame sections it would replace.
>>
>> If it worked, the "undwarf" unwinder would be a lot simpler than a real
>> DWARF unwinder.  And validating the sanity of the data at runtime would
>> be a lot more straightforward.  It could ensure that each stack pointer
>> is within the bounds of the current stack, like our current unwinder
>> does.
> 
> I've been hacking away at this, and so far it's working well.  The code
> is much simpler than a DWARF unwinder.  Right now the kernel piece is
> only ~350 lines of code.  The vast majority of the changes are in
> objtool.
> 
> It's now successfully unwinding through entry code and most other asm
> files, dumping entry regs, dealing with aligned stacks, dynamic stacks,
> etc.
> 
> Here's the struct in its current state:

How are you handling control flow?

	-hpa