Petr Vandrovec wrote:
+
+# Old-style boot protocol?
+old_cl:
+ push %ds # aka INITSEG
+ pop %fs
+
+ cmpw $0xa33f, (0x20)
+ jne done_cl # No command line at all?
+ movw (0x22), %si # Pointer relative to INITSEG
Perhaps you should convert ds:si to flat pointer and then this flat
pointer to fs:si using method above, to avoid problems with dword access
with si > 0xfffc or word access with si > 0xfffe ?
+
+# fs:si has the pointer to the command line now
+have_cl_pointer:
+
# loop through kernel command line one byte at a time
-cl_loop:
- cmpl $EDD_CL_EQUALS, (%si)
+cl_atspace:
+ movl %fs:(%si), %eax
This looks fine for new boot protocol, but what if old boot protocol
puts command line so that its last byte is at INITSEG:0xffff ? You get
#GP here, then, although command line is correctly zero terminated and
does not overflow segment.
With the old protocol, the command line is supposed to fit inside the
64K segment, so I don't think that's an issue. Putting "Hail Mary"
break at 0xfffd isn't a bad idea, though (especially since even if that
is legitimate, we can't fit "edd=" into that one.)
If si is 0xfffb here, bad things happen. I know, things I've pointed
out should not be problem in real world, and new code is definitely
better than old one, but if you already have code to avoid endless loop
if command line points to 64KB array of 0xFF let's do that right, no?
Agreed. I'll update the patch shortly.
-hpa
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