linux-kernel - Re: [PATCH] kbuild: include core debug info when DEBUG_INFO

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Message-ID: <87eglie87j.fsf@rasmusvillemoes.dk>
Date:	Thu, 11 Jun 2015 14:32:48 +0200
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Michal Marek <mmarek@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kbuild: include core debug info when DEBUG_INFO_REDUCED

On Sat, Mar 21 2015, Rasmus Villemoes <linux@...musvillemoes.dk> wrote:

> With CONFIG_DEBUG_INFO_REDUCED, we do get quite a lot of debug info
> (around 22.7 MB for a defconfig+DEBUG_INFO_REDUCED). However, the
> "basenames must match" rule used by -femit-struct-debug-baseonly
> option means that we miss some core data structures, such as struct
> {device, file, inode, mm_struct, page} etc.
>
> We can easily get these included as well, while still getting the
> benefits of CONFIG_DEBUG_INFO_REDUCED (faster build times and smaller
> individual object files): All it takes is a dummy translation unit
> including a few strategic headers and compiled with a flag overriding
> -femit-struct-debug-baseonly.
>
> This increases the size of .debug_info by ~0.3%, but these 90 KB
> contain some rather useful info.
>

Any comments on this patch? I know it's a little hacky, but I do find it
rather useful. For example, I just noticed that pahole shows this

struct audit_names {
        struct list_head           list;                 /*     0     0 */

        /* XXX 16 bytes hole, try to pack */

when applied to a vmlinux built with DEBUG_INFO_REDUCED, since debug
info for struct list_head is not included. The same is true for a lot of
other types which are often embedded in structs (e.g. spinlock_t and
atomic_t). I could of course just compile without DEBUG_INFO_REDUCED,
but the time and space savings of that are real and sad to lose (my tree
is 1.8 GB larger when I compile without it).

Rasmus
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