linux-kernel - Re: [PATCH 0/4] Compile kernel with -fwhole-program --combine

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 25 Aug 2006 08:01:27 +0200 (MEST)
From:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
To:	David Woodhouse <dwmw2@...radead.org>
cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] Compile kernel with -fwhole-program --combine

>> Compiling files on their own (`make drivers/foo/bar.o`) seems to make 
>> the optimization void. Sure, most people don't stop compiling in 
>> between. Just a note
>
>Actually I'm not entirely sure what you write is true. It'll _build_
>fs/jffs2/read.o, for example, but it still won't then use it when I make
>the kernel -- it'll just use fs/jffs2/jffs2.o which is built from all
>the C files with --combine. So the optimisation isn't lost.

Umm then it spends double the time in compilation, doing:

  read.o <- read.c
  foo.o <- foo.c
  bar.o <- bar.c
  built-in.o <- read.c foo.c bar.c

(cf. default current:
  built-in.o <- read.o foo.o bar.o)

>So to overcome this, we use GCC's __attribute__((externally_visible))
>which, as documented, just makes it global again -- undoing the effect
>of -fwhole-program just for this _one_ symbol.

Interesting. __attribute__((visibility("default"))) does the same?


Jan Engelhardt
-- 
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/