Change to deal with crappy GAS bug.

diff --git a/src/threads/loader.S b/src/threads/loader.S
index 811d2b60be1f2c89706d51ae4dd6ef48dea99792..2bfe1a45304c8756fb1cba4b14bd30af076c6320 100644 (file)
--- a/src/threads/loader.S
+++ b/src/threads/loader.S
@@ -70,12 +70,13 @@ start:
        cli
        cld
 
-# Set up data segments and stack.
+# Set up data segments.
 
        sub ax, ax
        mov es, ax
        mov ds, ax
 
+# Set up stack segment.
 # Stack grows downward starting from us.
 # We don't ever use the stack so this is strictly speaking
 # unnecessary.
@@ -109,7 +110,7 @@ start:
        mov al, 0xdf
        out 0x60, al
 
-#### Get memory size, via interrupt 15h function 88h.  Returns CF
+#### Get memory size, via interrupt 15h function 88h, which returns CF
 #### clear if successful, with AX = (kB of physical memory) - 1024.
 #### This only works for memory sizes <= 65 MB, which should be fine
 #### for our purposes.  We cap memory at 64 MB because that's all we
@@ -140,11 +141,17 @@ start:
 # Also add identical PDEs starting at LOADER_PHYS_BASE.
 # See [IA32-v3] section 3.7.6 for a description of the bits in eax.
 
+# A bug in some versions of GAS prevents us from using the straightforward
+#      mov es:[di + LOADER_PHYS_BASE / 1024 / 1024], eax
+# so we calculate the displacement in bx instead.
+
        mov eax, 0x11007
        mov ecx, 0x11
-       sub edi, edi
+       sub di, di
+       mov ebx, LOADER_PHYS_BASE
+       shr ebx, 20
 1:     mov es:[di], eax
-       mov es:LOADER_PHYS_BASE / 1024 / 1024[di], eax 
+       mov es:[bx + di], eax 
        add di, 4
        add eax, 0x1000
        loop 1b
@@ -155,8 +162,8 @@ start:
        mov ax, 0x1100
        mov es, ax
        mov eax, 0x7
-       mov ecx, 0x4000
-       sub edi, edi
+       mov cx, 0x4000
+       sub di, di
 1:     mov es:[di], eax 
        add di, 4 
        add eax, 0x1000
@@ -169,10 +176,6 @@ start:
        
 #### Switch to protected mode.
 
-# First we turn off interrupts because we don't set up an IDT.
-
-       cli
-
 # Then we point the GDTR to our GDT.  Protected mode requires a GDT.
 # We need a data32 prefix to ensure that all 32 bits of the GDT
 # descriptor are loaded (default is to load only 24 bits).