linux-kernel - mod_devicetable: Make dmi_strmatch.substr const char *

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Date:	Mon, 18 May 2015 17:07:35 -0700
From:	Joe Perches <joe@...ches.com>
To:	David Woodhouse <dwmw2@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Quentin Casasnovas <quentin.casasnovas@...cle.com>
Subject: mod_devicetable: Make dmi_strmatch.substr const char *

Hey David, Rusty, Quentin

This commit:
------------------------------
commit d945b697d0eea5a811ec299c5f1a25889bb0242b
From: David Woodhouse <dwmw2@...radead.org>
Date: Tue, 16 Sep 2008 16:23:28 -0700
Subject: [PATCH] Automatic MODULE_ALIAS() for DMI match tables.

This makes modpost handle MODULE_DEVICE_TABLE(dmi, xxxx).

I had to change the string pointers in the match table to char arrays,
and picked a size of 79 bytes almost at random -- do we need to make it
bigger than that? I was a bit concerned about the 'bloat' this
introduces into the match tables, but they should all be __initdata so
it shouldn't matter too much.

(Actually, modpost does go through the relocations and look at most of
them; it wouldn't be impossible to make it handle string pointers -- but
doesn't seem to be worth the effort, since they're __initdata).
------------------------------
	
changed dmi_strmatch.substr from char * to char[79];

Changing it back to const char * would shrink an x86-64
defconfig more than 100KB.

$ size vmlinux.old vmlinux.new
    text    data     bss      dec    hex filename
11941725 1825624 1085440 14852789 e2a2b5 vmlinux.old
11921172 1730648 1085440 14737260 e0df6c vmlinux.new

modpost has changed a bit since 2008, is it's time to change it back?

---
 include/linux/mod_devicetable.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

---
diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
index 7ab00d6..66c4309 100644
--- a/include/linux/mod_devicetable.h
+++ b/include/linux/mod_devicetable.h
@@ -462,7 +462,7 @@ enum dmi_field {
 struct dmi_strmatch {
 	unsigned char slot:7;
 	unsigned char exact_match:1;
-	char substr[79];
+	const char *substr;
 };
 
 struct dmi_system_id {


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