[syslinux:elflink] 4k_sector: Save some bytes adding a function to set bx before read_sector

[syslinux-bot for Frediano Ziglio]

Commit-ID:  b681bd70ac5c478c2d450aa1db98aa9359625a7d
Gitweb:     http://www.syslinux.org/commit/b681bd70ac5c478c2d450aa1db98aa9359625a7d
Author:     Frediano Ziglio <frediano.ziglio at citrix.com>
AuthorDate: Fri, 8 Feb 2013 12:58:34 +0000
Committer:  Matt Fleming <matt.fleming at intel.com>
CommitDate: Mon, 11 Feb 2013 12:35:12 +0000

4k_sector: Save some bytes adding a function to set bx before read_sector

Mostly of the time bx was set as phdr before calling read_sector
so add a specific function to set %bx and call read_sector
gaining 2 bytes

Signed-off-by: Frediano Ziglio <frediano.ziglio at citrix.com>
Signed-off-by: Matt Fleming <matt.fleming at intel.com>

---
 mbr/gptmbr.S | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/mbr/gptmbr.S b/mbr/gptmbr.S
index ef2235d..b9c0777 100644
--- a/mbr/gptmbr.S
+++ b/mbr/gptmbr.S
@@ -118,14 +118,11 @@ next:
 	xorl	%eax,%eax
 	cltd
 	incw	%ax		/* %edx:%eax = 1 */
-	movw	$phdr, %bx
-	pushw	%bx		/* -8(%bp) phdr == bootsect */
-	call	read_sector
+	call	read_sector_phdr
 
 	/* Number of partition sectors */
 	/* We assume the partition table is 32K or less, and that
 	   the sector size is 512. */
-	/* Note: phdr == 6(%bp) */
 	movw	(80+6)(%bp),%cx		/* NumberOfPartitionEntries */
 	movw	(84+6)(%bp),%ax		/* SizeOfPartitionEntry */
 	pushw	%ax
@@ -215,8 +212,7 @@ found_part:
 boot:
 	movl	(32+20)(%si),%eax
 	movl	(36+20)(%si),%edx
-	popw	%bx
-	call	read_sector
+	call	read_sector_phdr
 	cmpw	$0xaa55, -2(%bx)
 	jne	missing_os	/* Not a valid boot sector */
 	movw	%bp, %sp	/* driveno == bootsec-6 */
@@ -238,6 +234,11 @@ saturate_stosl:
 1:	stosl
 	ret
 
+read_sector_phdr:
+	movw	$phdr, %bx
+
+	/* fall through and read sector */
+
 /*
  * read_sector: read a single sector pointed to by %edx:%eax to
  * %es:%bx.  CF is set on error.  All registers saved.