[syslinux] Linker script assertion with binutils 2.21

[Colin Watson]

On Mon, Jan 17, 2011 at 11:41:01AM -0800, H. Peter Anvin wrote:
> The assertion in the linker script compares the symbols
> syslinux_ldlinux_size (from the assembler) with __payload_len (from the
> linker).  Comment out the assert and check the value of __payload_len in
> syslinux.elf; if it is something other than 0x7c00 we need to find out
> where it gets the value (by backtracking the component values.)

Thanks:

  $ objdump -t syslinux.elf  | grep payload
  ffff8400 l    d  .payload       00000000 .payload
  00000200 g       *ABS*  00000000 __payload_lma
  40000000 g       *ABS*  00000000 __payload_dwords
  fffff840 g       *ABS*  00000000 __payload_sseg
  ffff8400 g       .payload       00000000 __payload_start
  ffff8400 g       .payload       00007c00 syslinux_ldlinux
  00000000 g       .payload       00000000 __payload_end
  00000000 g       .payload       00000000 __payload_len

Looks like subtracting one relative address from another doesn't work
right, at least not when one is negative.  This fixes it, but I haven't
tested it with binutils < 2.21 (although ABSOLUTE predates the commit I
referred to in my original post, at least):

diff --git a/dos/dosexe.ld b/dos/dosexe.ld
index c67c506..423fd62 100644
--- a/dos/dosexe.ld
+++ b/dos/dosexe.ld
@@ -28,9 +28,9 @@ SECTIONS
 
 	. = 0x100000000 - syslinux_ldlinux_size;
 	.payload : AT (__payload_lma) {
-		 __payload_start = .;
+		 __payload_start = ABSOLUTE(.);
 		 *(.payload)
-		 __payload_end = .;
+		 __payload_end = ABSOLUTE(.);
 	}
 	__payload_len = __payload_end - __payload_start;
 	__payload_dwords = __payload_len >> 2;

-- 
Colin Watson                                       [cjwatson at ubuntu.com]