shuffler: work around KVM problem with the new shuffler

KVM uses V86 mode to simulate real mode.  This causes problems with
the new shuffler.  This changes the shuffler handover to be in
16-bit protected mode instead, and requires the stub to do the actual
entry to real mode.  For the KVM hack to work, all segments must have:

(seg.base & 0xfff0000f) == 0 && seg.limit == 0xffff

As a result, we have to make sure the real-mode entry stub is
paragraph-aligned, lest we violate the first criterion.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 14 insertions, 1 deletions

diff --git a/core/syslinux.ld b/core/syslinux.ld
index 6f7f5a78..c1da230e 100644
--- a/core/syslinux.ld
+++ b/core/syslinux.ld
@@ -44,7 +44,7 @@ SECTIONS
 	__bss_len = __bss_end - __bss_start;
 	__bss_dwords = (__bss_len + 3) >> 2;
 
-	.config : AT (__config_lma) {
+ 	.config : AT (__config_lma) {
 		__config_start = .;
 		*(.config)
 		__config_end = .;
@@ -52,6 +52,15 @@ SECTIONS
 	__config_len = __config_end - __config_start;
 	__config_dwords = (__config_len + 3) >> 2;
 
+	. = ALIGN(16);
+ 	.replacestub : AT (__replacestub_lma) {
+		__replacestub_start = .;
+		*(.replacestub)
+		__replacestub_end = .;
+	}
+	__replacestub_len = __replacestub_end - __replacestub_start;
+	__replacestub_dwords = (__replacestub_len + 3) >> 2;
+
 	/* Stack */
 
 	STACK_BASE = 0x7c00 - STACK_LEN;
@@ -99,6 +108,10 @@ SECTIONS
 	__config_lma = .;
 	. += SIZEOF(.config);
 
+	. = ALIGN(4);
+	__replacestub_lma = .;
+	. += SIZEOF(.replacestub);
+
 	/* ADV, must be the last intialized section */
 
 	. = ALIGN(512);