e820: pre-initialize buffer

Pre-initialize the e820 buffer to all zero, except for the active bit;
we have found that BIOSes will make assumptions about the pre-existing
value of the buffer and this seems the most conservative value.

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

diff --git a/com32/lib/syslinux/memmap.c b/com32/lib/syslinux/memmap.c
index e14dd70..105c947 100644 (file)
--- a/com32/lib/syslinux/memmap.c
+++ b/com32/lib/syslinux/memmap.c
@@ -78,6 +78,8 @@ struct syslinux_memmap *syslinux_memory_map(void)
   ireg.ecx.l    = sizeof(*e820buf);
   ireg.es       = SEG(e820buf);
   ireg.edi.w[0] = OFFS(e820buf);
+  memset(e820buf, 0, sizeof *e820buf);
+  e820buf->extattr = 1;
 
   do {
     __intcall(0x15, &ireg, &oreg);

diff --git a/core/highmem.inc b/core/highmem.inc
index 7341bf2..69652b7 100644 (file)
--- a/core/highmem.inc
+++ b/core/highmem.inc
@@ -40,6 +40,11 @@ get_e820:
                mov dword [E820Max],-(1 << 20)  ; Max amount of high memory
                mov dword [E820Mem],(1 << 20)   ; End of detected high memory
 .start_over:
+               mov di,E820Buf
+               xor ax,ax
+               mov cx,12
+               rep stosw                       ; Clear buffer
+               mov byte [di-4],01h             ; Initial extattr value
                xor ebx,ebx                     ; Start with first record
                jmp short .do_e820              ; Skip "at end" check first time!
 .int_loop:     and ebx,ebx                     ; If we're back at beginning...

diff --git a/memdisk/msetup.c b/memdisk/msetup.c
index 60149c3..a206701 100644 (file)
--- a/memdisk/msetup.c
+++ b/memdisk/msetup.c
@@ -45,6 +45,8 @@ static inline int get_e820(void)
   com32sys_t regs;
 
   memset(&regs, 0, sizeof regs);
+  memset(buf, 0, sizeof *buf);
+  buf->extattr = 1;
 
   do {
     regs.eax.l = 0x0000e820;