From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
live-patching@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Andy Lutomirski <luto@kernel.org>, Jiri Slaby <jslaby@suse.cz>,
"H. Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v2 4/8] objtool: add undwarf debuginfo generation
Date: Thu, 29 Jun 2017 09:04:04 -0500 [thread overview]
Message-ID: <20170629140404.qgcvxhcgm7iywrkb@treble> (raw)
In-Reply-To: <20170629072512.pmkfnrgq4dci6od7@gmail.com>
On Thu, Jun 29, 2017 at 09:25:12AM +0200, Ingo Molnar wrote:
> > +/*
> > + * This struct contains a simplified version of the DWARF Call Frame
> > + * Information standard. It contains only the necessary parts of the real
> > + * DWARF, simplified for ease of access by the in-kernel unwinder. It tells
> > + * the unwinder how to find the previous SP and BP (and sometimes entry regs)
> > + * on the stack for a given code address (IP). Each instance of the struct
> > + * corresponds to one or more code locations.
> > + */
> > +struct undwarf {
> > + short cfa_offset;
> > + short bp_offset;
> > + unsigned cfa_reg:4;
> > + unsigned bp_reg:4;
> > + unsigned type:2;
> > +};
>
> I never know straight away what 'CFA' stands for - could we please use natural
> names, i.e. something like:
>
> struct undwarf {
> u16 sp_offset;
> u16 bp_offset;
> unsigned sp_reg:4;
> unsigned bp_reg:4;
> unsigned type:2;
> };
>
> ...
>
> struct unwind_hint {
> u32 ip;
> u16 sp_offset;
> u8 sp_reg;
> u8 type;
> };
>
> ?
>
> Also note the slightly cleaner vertical alignment, plus the conversion to more
> stable data types: I believe various bits of tooling (perf and so) will eventually
> learn about undwarf, so having a well defined cross-arch data structure is
> probably of advantage.
I agree with all your suggestions.
(Though if we want to make it truly cross-arch, 'bp' should be 'fp', for
frame pointer. But there were some objections to that, so I'll leave it
'bp' for now.)
> Since we are not bound by DWARF anymore, we might as well use readable names and
> such?
>
> Plus, shouldn't we use __packed for 'struct undwarf' to minimize the structure's
> size (to 6 bytes AFAICS?) - or is optimal packing of the main undwarf array
> already guaranteed on every platform with this layout?
Ah yes, it should definitely be packed (assuming that doesn't affect
performance negatively).
--
Josh
next prev parent reply other threads:[~2017-06-29 14:04 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-28 15:11 [PATCH v2 0/8] x86: undwarf unwinder Josh Poimboeuf
2017-06-28 15:11 ` [PATCH v2 1/8] objtool: move checking code to check.c Josh Poimboeuf
2017-06-30 13:12 ` [tip:core/objtool] objtool: Move " tip-bot for Josh Poimboeuf
2017-06-28 15:11 ` [PATCH v2 2/8] objtool, x86: add several functions and files to the objtool whitelist Josh Poimboeuf
2017-06-30 13:12 ` [tip:core/objtool] objtool, x86: Add " tip-bot for Josh Poimboeuf
2017-06-28 15:11 ` [PATCH v2 3/8] objtool: stack validation 2.0 Josh Poimboeuf
2017-06-30 8:32 ` Ingo Molnar
2017-06-30 13:23 ` Josh Poimboeuf
2017-06-30 13:26 ` Josh Poimboeuf
2017-06-30 14:09 ` [PATCH] objtool: silence warnings for functions which use iret Josh Poimboeuf
2017-06-30 17:49 ` [tip:core/objtool] objtool: Silence warnings for functions which use IRET tip-bot for Josh Poimboeuf
2017-06-30 13:13 ` [tip:core/objtool] objtool: Implement stack validation 2.0 tip-bot for Josh Poimboeuf
2017-06-28 15:11 ` [PATCH v2 4/8] objtool: add undwarf debuginfo generation Josh Poimboeuf
2017-06-29 7:14 ` Ingo Molnar
2017-06-29 13:40 ` Josh Poimboeuf
2017-06-29 7:25 ` Ingo Molnar
2017-06-29 14:04 ` Josh Poimboeuf [this message]
2017-06-29 14:46 ` Ingo Molnar
2017-06-29 15:06 ` Josh Poimboeuf
2017-07-06 20:36 ` Josh Poimboeuf
2017-07-07 9:44 ` Ingo Molnar
2017-07-11 2:58 ` Josh Poimboeuf
2017-07-11 8:40 ` Ingo Molnar
2017-06-28 15:11 ` [PATCH v2 5/8] objtool, x86: add facility for asm code to provide unwind hints Josh Poimboeuf
2017-06-28 15:11 ` [PATCH v2 6/8] x86/entry: add unwind hint annotations Josh Poimboeuf
2017-06-29 17:53 ` Josh Poimboeuf
2017-06-29 18:50 ` Andy Lutomirski
2017-06-29 19:05 ` Josh Poimboeuf
2017-06-29 21:09 ` Andy Lutomirski
2017-06-29 21:41 ` Josh Poimboeuf
2017-06-29 22:59 ` Andy Lutomirski
2017-06-30 2:12 ` Josh Poimboeuf
2017-06-30 5:05 ` Andy Lutomirski
2017-06-30 5:41 ` Andy Lutomirski
2017-06-30 13:11 ` Josh Poimboeuf
2017-06-30 15:44 ` Andy Lutomirski
2017-06-30 15:55 ` Josh Poimboeuf
2017-06-30 15:56 ` Andy Lutomirski
2017-06-30 16:16 ` Josh Poimboeuf
2017-06-28 15:11 ` [PATCH v2 7/8] x86/asm: add unwind hint annotations to sync_core() Josh Poimboeuf
2017-06-28 15:11 ` [PATCH v2 8/8] x86/unwind: add undwarf unwinder Josh Poimboeuf
2017-06-29 7:55 ` [PATCH v2 0/8] x86: " Ingo Molnar
2017-06-29 14:12 ` Josh Poimboeuf
2017-06-29 19:13 ` Josh Poimboeuf
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