dos: change the link procedure to use negative pointers below DGROUP

Use negative pointer values below DGROUP, i.e. for the .payload
segment.  This makes it a lot easier to figure out if we are dealing
with pointers that shouldn't come from where they do, since the DGROUP
and .payload segments no longer overlap, and in fact are congruent.

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

4 files changed, 10 insertions, 10 deletions

diff --git a/dos/Makefile b/dos/Makefile
index 3d19ff29..9f48962b 100755
--- a/dos/Makefile
+++ b/dos/Makefile
@@ -31,10 +31,10 @@ SRCS     = syslinux.c \
 	   ../libinstaller/syslxopt.c \
 	   ../libinstaller/setadv.c \
 	   ../libinstaller/bootsect_bin.c \
-	   ../libinstaller/ldlinux_bin.c \
 	   ../libinstaller/mbr_bin.c \
            $(wildcard ../libfat/*.c)
-OBJS	 = header.o crt0.o $(patsubst %.c,%.o,$(notdir $(SRCS)))
+OBJS	 = header.o crt0.o ldlinux.o \
+	   $(patsubst %.c,%.o,$(notdir $(SRCS)))
 LIBOBJS	 = int2526.o conio.o memcpy.o memset.o memmove.o skipatou.o atou.o \
 	   malloc.o free.o getopt_long.o getsetsl.o strchr.o strtoul.o \
 	   strntoumax.o argv.o printf.o __divdi3.o __udivmoddi4.o
diff --git a/dos/dosexe.ld b/dos/dosexe.ld
index 4612b30a..c67c5060 100755
--- a/dos/dosexe.ld
+++ b/dos/dosexe.ld
@@ -26,20 +26,22 @@ SECTIONS
 	__header_size = .;
 	__payload_lma = .;
 
-	. = 0;
+	. = 0x100000000 - syslinux_ldlinux_size;
 	.payload : AT (__payload_lma) {
 		 __payload_start = .;
-		 ldlinux_bin.o(.data)
+		 *(.payload)
 		 __payload_end = .;
 	}
 	__payload_len = __payload_end - __payload_start;
 	__payload_dwords = __payload_len >> 2;
 
-	. = ALIGN(16);
-	__text_lma = __payload_lma + .;
+	__text_lma = __payload_lma + syslinux_ldlinux_size;
 	__payload_sseg = (__payload_lma - __text_lma) >> 4;
 	_exe_text_seg  = (__text_lma - __header_size) >> 4;
 
+	__assert1 = ASSERT((__payload_len == syslinux_ldlinux_size),
+	"syslinux_ldlinux_size must equal the size of .payload");
+
 	. = 0;
 	.text : AT (__text_lma) {
 		*(.text .stub .text.* .gnu.linkonce.t.*)
diff --git a/dos/getsetsl.c b/dos/getsetsl.c
index a48f3df2..5c1dbbda 100644
--- a/dos/getsetsl.c
+++ b/dos/getsetsl.c
@@ -87,7 +87,7 @@ void memcpy_to_sl(void *dst, const void *src, size_t len)
     uint16_t seg;
     uint16_t off;
 
-    seg = ldlinux_seg + ((size_t)dst >> 4);
+    seg = ds() + ((size_t)dst >> 4);
     off = (size_t)dst & 15;
 
     asm volatile("pushw %%es ; "
diff --git a/libinstaller/syslxint.h b/libinstaller/syslxint.h
index f16c2e5c..b8e872a7 100644
--- a/libinstaller/syslxint.h
+++ b/libinstaller/syslxint.h
@@ -111,8 +111,6 @@ static inline void set_64(uint64_t *p, uint64_t v)
  */
 #ifdef __MSDOS__
 
-extern uint16_t ldlinux_seg;	/* Defined in dos/syslinux.c */
-
 static inline __attribute__ ((const))
 uint16_t ds(void)
 {
@@ -125,7 +123,7 @@ static inline void *set_fs(const void *p)
 {
     uint16_t seg;
 
-    seg = ldlinux_seg + ((size_t) p >> 4);
+    seg = ds() + ((size_t) p >> 4);
     asm volatile ("movw %0,%%fs"::"rm" (seg));
     return (void *)((size_t) p & 0xf);
 }