From: Ingo Molnar <mingo@kernel.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
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 09:25:12 +0200 [thread overview]
Message-ID: <20170629072512.pmkfnrgq4dci6od7@gmail.com> (raw)
In-Reply-To: <e255ec17d43e4a22b58accb42380fe78250cafe8.1498659915.git.jpoimboe@redhat.com>
* Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> +#ifndef _UNDWARF_TYPES_H
> +#define _UNDWARF_TYPES_H
> +
> +/*
> + * The UNDWARF_REG_* registers are base registers which are used to find other
> + * registers on the stack.
> + *
> + * The CFA (call frame address) is the value of the stack pointer on the
> + * previous frame, i.e. the caller's SP before it called the callee.
> + *
> + * The CFA is usually based on SP, unless a frame pointer has been saved, in
> + * which case it's based on BP.
> + *
> + * BP is usually either based on CFA or is undefined (meaning its value didn't
> + * change for the current frame).
> + *
> + * So the CFA base is usually either SP or BP, and the FP base is usually either
> + * CFA or undefined. The rest of the base registers are needed for special
> + * cases like entry code and gcc aligned stacks.
> + */
> +#define UNDWARF_REG_UNDEFINED 0
> +#define UNDWARF_REG_CFA 1
> +#define UNDWARF_REG_DX 2
> +#define UNDWARF_REG_DI 3
> +#define UNDWARF_REG_BP 4
> +#define UNDWARF_REG_SP 5
> +#define UNDWARF_REG_R10 6
> +#define UNDWARF_REG_R13 7
> +#define UNDWARF_REG_BP_INDIRECT 8
> +#define UNDWARF_REG_SP_INDIRECT 9
> +#define UNDWARF_REG_MAX 15
> +
> +/*
> + * UNDWARF_TYPE_CFA: Indicates that cfa_reg+cfa_offset points to the caller's
> + * stack pointer (aka the CFA in DWARF terms). Used for all callable
> + * functions, i.e. all C code and all callable asm functions.
> + *
> + * UNDWARF_TYPE_REGS: Used in entry code to indicate that cfa_reg+cfa_offset
> + * points to a fully populated pt_regs from a syscall, interrupt, or exception.
> + *
> + * UNDWARF_TYPE_REGS_IRET: Used in entry code to indicate that
> + * cfa_reg+cfa_offset points to the iret return frame.
> + */
> +#define UNDWARF_TYPE_CFA 0
> +#define UNDWARF_TYPE_REGS 1
> +#define UNDWARF_TYPE_REGS_IRET 2
> +
> +/*
> + * 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.
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?
Thanks,
Ingo
next prev parent reply other threads:[~2017-06-29 7:25 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 [this message]
2017-06-29 14:04 ` Josh Poimboeuf
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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