[prefix] Use %cs as implicit parameter to uninstall()

romprefix.S currently calls uninstall() with an invalid value in %ax. Consequently, base memory is not freed after a ROM boot attempt (or after entering iPXE during POST). The uninstall() function is physically present in .text16, and so can use %cs to determine the .text16 segment address. The .data16 segment address is not required, since uninstall() is called only by code paths which set up .data16 to immediately follow .text16. Signed-off-by: Michael Brown <mcb30@ipxe.org>
ipxe · Mar 8, 2013 · 0d4a760 · 0d4a760
1 parent c7694ac
commit 0d4a760
Showing 1 changed file with 6 additions and 6 deletions.
diff --git a/src/arch/i386/prefix/libprefix.S b/src/arch/i386/prefix/libprefix.S
@@ -545,8 +545,7 @@ alloc_basemem:
  * Free space allocated with alloc_basemem.
  *
  * Parameters:
- *   %ax : .text16 segment address
- *   %bx : .data16 segment address
+ *   none (.text16 segment address is implicit in %cs)
  * Returns:
  *   %ax : 0 if successfully freed
  * Corrupts:
@@ -559,28 +558,30 @@ alloc_basemem:
 free_basemem:
 	/* Preserve registers */
 	pushw	%fs
+	pushw	%ax
 
 	/* Check FBMS counter */
-	pushw	%ax
+	movw	%cs, %ax
 	shrw	$6, %ax
 	pushw	$0x40
 	popw	%fs
 	cmpw	%ax, %fs:0x13
-	popw	%ax
 	jne	1f
 
 	/* Check hooked interrupt count */
 	cmpw	$0, %cs:hooked_bios_interrupts
 	jne	1f
 
 	/* OK to free memory */
+	movw	%cs, %ax
 	addw	$_text16_memsz_pgh, %ax
 	addw	$_data16_memsz_pgh, %ax
 	shrw	$6, %ax
 	movw	%ax, %fs:0x13
 	xorw	%ax, %ax
 
 1:	/* Restore registers and return */
+	popw	%ax
 	popw	%fs
 	ret
 	.size free_basemem, . - free_basemem
@@ -872,8 +873,7 @@ close_payload:
  * Uninstall all text and data segments.
  *
  * Parameters:
- *   %ax  : .text16 segment address
- *   %bx  : .data16 segment address
+ *   none (.text16 segment address is implicit in %cs)
  * Returns:
  *   none
  * Corrupts: