dos: We cannot use memset() for a far object, introduce memset_sl()

We started using memset() on the extents buffer in ldlinux.sys, which
doesn't reside in the main segment, which worked on all the installer
platforms except DOS.  Fix DOS by introducing memset_sl() for this
case.

Reported-by: Ady <ady-sf@hotmail.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/dos/getsetsl.c b/dos/getsetsl.c
index fadef438..5260a2a1 100644
--- a/dos/getsetsl.c
+++ b/dos/getsetsl.c
@@ -123,3 +123,20 @@ void memcpy_from_sl(void *dst, const void *src, size_t len)
 		 : "r" (seg)
 		 : "memory");
 }
+
+void memset_sl(void *dst, int c, size_t len)
+{
+    uint16_t seg;
+    uint16_t off;
+
+    seg = ds() + ((size_t)dst >> 4);
+    off = (size_t)dst & 15;
+
+    asm volatile("pushw %%es ; "
+		 "movw %3,%%es ; "
+		 "rep ; stosb ; "
+		 "popw %%es"
+		 : "+D" (off), "+c" (len)
+		 : "a" (c), "r" (seg)
+		 : "memory");
+}