Add support for "pseudo-kernels" < 64K in size.

4 files changed, 44 insertions, 6 deletions

diff --git a/NEWS b/NEWS
index f18dc3e0..6c307067 100644
--- a/NEWS
+++ b/NEWS
@@ -7,6 +7,8 @@ Changes in 1.65:
 	  correctly; unfortunately many BIOSes apparently don't.
 	* Support Linux boot protocol version 2.03 (explicitly
 	  specify the initrd address limit.)
+	* Handle small "pseudo-kernels"; images that use the Linux
+	  kernel boot protocols but are less than 64K in size.
 
 Changes in 1.64:
 	* Limited support for hardware flow control when using a
diff --git a/isolinux.asm b/isolinux.asm
index 5aaa3d06..1c165bc2 100644
--- a/isolinux.asm
+++ b/isolinux.asm
@@ -1726,14 +1726,20 @@ kernel_good:
 ; kernel code.	The boot sector is never executed when using an external
 ; booting utility, but it contains some status bytes that are necessary.
 ;
-; First check that our kernel is at least 64K and less than 8M (if it is
+; First check that our kernel is at least 1K and less than 8M (if it is
 ; more than 8M, we need to change the logic for loading it anyway...)
 ;
+; We used to require the kernel to be 64K or larger, but it has gotten
+; popular to use the Linux kernel format for other things, which may
+; not be so large.
+;
 is_linux_kernel:
                 cmp dx,80h			; 8 megs
 		ja kernel_corrupt
 		and dx,dx
-		jz kernel_corrupt
+		jnz kernel_sane
+		cmp ax,1024			; Bootsect + 1 setup sect
+		jb near kernel_corrupt
 kernel_sane:	push ax
 		push dx
 		push si
@@ -1775,6 +1781,10 @@ kernel_sane:	push ax
 		call abort_check		; Check for abort key
 		mov cx,[ClustPerMoby]
 		shr cx,1			; Half a moby
+		cmp cx,[KernelClust]
+		jna .normalkernel
+		mov cx,[KernelClust]
+.normalkernel:
 		sub [KernelClust],cx
 		xor bx,bx
                 pop si                          ; Cluster pointer on stack
@@ -2016,6 +2026,8 @@ high_load_loop:
                 call cwritestr
                 call abort_check
                 mov cx,[KernelClust]
+		and cx,cx
+		jz high_load_done		; Zero left (tiny kernel?)
 		cmp cx,[ClustPerMoby]
 		jna high_last_moby
 		mov cx,[ClustPerMoby]
diff --git a/ldlinux.asm b/ldlinux.asm
index 6b5a9ba9..eabc3122 100644
--- a/ldlinux.asm
+++ b/ldlinux.asm
@@ -1774,14 +1774,20 @@ kernel_good:
 ; stuff means 512 bytes *no matter what*, so here I am using that piece
 ; of knowledge.
 ;
-; First check that our kernel is at least 64K and less than 8M (if it is
+; First check that our kernel is at least 1K and less than 8M (if it is
 ; more than 8M, we need to change the logic for loading it anyway...)
 ;
+; We used to require the kernel to be 64K or larger, but it has gotten
+; popular to use the Linux kernel format for other things, which may
+; not be so large.
+;
 is_linux_kernel:
                 cmp dx,80h			; 8 megs
 		ja kernel_corrupt
 		and dx,dx
-		jz kernel_corrupt
+		jnz kernel_sane
+		cmp ax,1024			; Bootsect + 1 setup sect
+		jb kernel_corrupt
 kernel_sane:	push ax
 		push dx
 		push si
@@ -1823,6 +1829,10 @@ kernel_sane:	push ax
 		call abort_check		; Check for abort key
 		mov cx,[ClustPerMoby]
 		shr cx,1			; Half a moby
+		cmp cx,[KernelClust]
+		jna .normalkernel
+		mov cx,[KernelClust]
+.normalkernel:
 		sub [KernelClust],cx
 		xor bx,bx
                 pop si                          ; Cluster pointer on stack
@@ -2121,6 +2131,8 @@ high_load_loop:
                 call cwritestr
                 call abort_check
                 mov cx,[KernelClust]
+		and cx,cx
+		jz high_load_done		; Zero left (tiny kernel?)
 		cmp cx,[ClustPerMoby]
 		jna high_last_moby
 		mov cx,[ClustPerMoby]
diff --git a/pxelinux.asm b/pxelinux.asm
index 1bf8060e..3dfdfa4c 100644
--- a/pxelinux.asm
+++ b/pxelinux.asm
@@ -1523,14 +1523,20 @@ kernel_good:
 ; kernel code.	The boot sector is never executed when using an external
 ; booting utility, but it contains some status bytes that are necessary.
 ;
-; First check that our kernel is at least 64K and less than 8M (if it is
+; First check that our kernel is at least 1K and less than 8M (if it is
 ; more than 8M, we need to change the logic for loading it anyway...)
 ;
+; We used to require the kernel to be 64K or larger, but it has gotten
+; popular to use the Linux kernel format for other things, which may
+; not be so large.
+;
 is_linux_kernel:
                 cmp dx,80h			; 8 megs
 		ja kernel_corrupt
 		and dx,dx
-		jz kernel_corrupt
+		jnz kernel_sane
+		cmp ax,1024			; Bootsect + 1 setup sect
+		jb kernel_corrupt
 kernel_sane:	push ax
 		push dx
 		push si
@@ -1572,6 +1578,10 @@ kernel_sane:	push ax
 		call abort_check		; Check for abort key
 		mov cx,[ClustPerMoby]
 		shr cx,1			; Half a moby
+		cmp cx,[KernelClust]
+		jna .normalkernel
+		mov cx,[KernelClust]
+.normalkernel:
 		sub [KernelClust],cx
 		xor bx,bx
                 pop si                          ; Cluster pointer on stack
@@ -1821,6 +1831,8 @@ high_load_loop:
                 call cwritestr
                 call abort_check
                 mov cx,[KernelClust]
+		and cx,cx
+		jz high_load_done		; Zero left (tiny kernel?)
 		cmp cx,[ClustPerMoby]
 		jna high_last_moby
 		mov cx,[ClustPerMoby]