[memdisk] Make ES:DI point to the $PnP structure on entry

ES:DI is supposed to point to the $PnP structure on entry, make it sew.

2 files changed, 44 insertions, 7 deletions

diff --git a/memdisk/memdisk16.asm b/memdisk/memdisk16.asm
index 37e85967..ebcfe7e8 100644
--- a/memdisk/memdisk16.asm
+++ b/memdisk/memdisk16.asm
@@ -133,20 +133,22 @@ copy_cmdline:
 ; When init32 returns, we have been set up, the new boot sector loaded,
 ; and we should go and and run the newly loaded boot sector
 ;
-; The setup function returns (in AL) the drive number which should be
-; put into DL
+; The setup function returns (in DX) the drive number, and
+; the value for ES:DI in AX
 ;
-		mov dx,ax
+		movzx edi,ax
+		shr eax,16
+		mov es,ax
 
 		cli
 		xor esi,esi		; No partition table involved
 		mov ds,si		; Make all the segments consistent
-		mov es,si
 		mov fs,si
 		mov gs,si
 		mov ss,si
 		mov esp,0x7C00		; Good place for SP to start out
-		jmp 0:0x7C00
+		call 0:0x7C00
+		int 18h			; A far return -> INT 18h
 
 ;
 ; We enter protected mode, set up a flat 32-bit environment, run rep movsd
diff --git a/memdisk/setup.c b/memdisk/setup.c
index 2f41a4d9..fe8023b1 100644
--- a/memdisk/setup.c
+++ b/memdisk/setup.c
@@ -498,6 +498,33 @@ void __attribute__((noreturn)) die(void)
     asm volatile("hlt");
 }
 
+/*
+ * Find a $PnP installation check structure; return (ES << 16) + DI value
+ */
+static uint32_t pnp_install_check(void)
+{
+  uint32_t *seg;
+  unsigned char *p, csum;
+  int i;
+
+  for (seg = (uint32_t *)0xf0000; seg < (uint32_t *)0x100000; seg += 4) {
+    if (*seg == ('$'+('P' << 8)+('n' << 16)+('P' << 24))) {
+      p = (unsigned char *)seg;
+      if (p[2] < 0x21)
+	continue;
+      csum = 0;
+      for (i = p[2]; i; i--)
+	csum += *p++;
+      if (csum != 0)
+	continue;
+
+      return (0xf000 << 16) + (uint16_t)(unsigned long)seg;
+    }
+  }
+
+  return 0;
+}
+
 #define STACK_NEEDED	512	/* Number of bytes of stack */
 
 /*
@@ -508,7 +535,12 @@ void __attribute__((noreturn)) die(void)
 syscall_t syscall;
 void *sys_bounce;
 
-uint32_t setup(syscall_t cs_syscall, void *cs_bounce)
+struct setup_return {
+  uint32_t es;			/* ES:DI -> $PnP structure */
+  uint32_t dx;			/* DL -> boot device */
+};
+
+struct setup_return setup(syscall_t cs_syscall, void *cs_bounce)
 {
   unsigned int bin_size = (int) &_binary_memdisk_bin_size;
   struct memdisk_header *hptr;
@@ -521,6 +553,7 @@ uint32_t setup(syscall_t cs_syscall, void *cs_bounce)
   int total_size, cmdlinelen;
   com32sys_t regs;
   uint32_t ramdisk_image, ramdisk_size;
+  struct setup_return sr;
 
   /* Set up global variables */
   syscall = cs_syscall;
@@ -776,5 +809,7 @@ uint32_t setup(syscall_t cs_syscall, void *cs_bounce)
   puts("booting...\n");
 
   /* On return the assembly code will jump to the boot vector */
-  return geometry->driveno;
+  sr.esdi = pnp_install_check();
+  sr.dx = geometry->driveno;
+  return sr;
 }