linux-kernel - Re: Testing of function/data-sections on linux-2.6.35-rc4

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Message-ID: <20100723202946.GA27288@merkur.ravnborg.org>
Date:	Fri, 23 Jul 2010 22:29:46 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Denys Vlasenko <vda.linux@...glemail.com>
Cc:	Tim Abbott <tabbott@...lice.com>, Tim Bird <tim.bird@...sony.com>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	linux-kernel@...r.kernel.org,
	Matt Fleming <matt@...sole-pimps.org>,
	linux-arch@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	Michal Marek <mmarek@...e.cz>,
	Parisc List <linux-parisc@...r.kernel.org>
Subject: Re: Testing of function/data-sections on linux-2.6.35-rc4

> * fix for module linker script: linux-2.6.35-rc4-fs.fix-ko-module-linker-script.patch
>   Prevents kernel modules from having unnecessarily many
>   sections and thus prevents module size growth.

Acked-by: Sam Ravnborg <sam@...nborg.org>

--- linux-2.6.35-rc4/scripts/module-common.lds
+++ linux-2.6.35-rc4.new/scripts/module-common.lds
@@ -3,6 +3,29 @@
  * Archs are free to supply their own linker scripts.  ld will
  * combine them automatically.
  */
+
+/* .data.foo are generated by gcc itself with -fdata-sections,
+ * whereas double-dot sections (like .data..percpu) are generated
+ * by kernel's magic macros.
+ *
+ * Since this script does not specify what to do with double-dot sections,
+ * ld -r will coalesce all .data..foo input sections into one .data..foo
+ * output section, all .data..bar input sections into one .data..bar
+ * output section and so on. This is exactly what we want.
+ *
+ * Same goes for .text, .bss and .rodata. In case of .rodata, various
+ * .rodata.foo sections are generated by gcc even without -fdata-sections
+ */
+
 SECTIONS {
+
+	/* Coalesce sections produced by gcc -ffunction-sections */
+	.text   0 : AT(0) { *(.text .text.[A-Za-z0-9_$^]*) }
+
+	/* Coalesce sections produced by gcc -fdata-sections */
+	.rodata 0 : AT(0) { *(.rodata .rodata.[A-Za-z0-9_$^]*) }
+	.data   0 : AT(0) { *(.data .data.[A-Za-z0-9_$^]*) }
+	.bss    0 : AT(0) { *(.bss .bss.[A-Za-z0-9_$^]*) }
+
 	/DISCARD/ : { *(.discard) }
 }
--
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