diff options
Diffstat (limited to 'arch/i386/boot/edd.S')
| -rw-r--r-- | arch/i386/boot/edd.S | 97 |
1 files changed, 75 insertions, 22 deletions
diff --git a/arch/i386/boot/edd.S b/arch/i386/boot/edd.S index 4b84ea2..3432136 100644 --- a/arch/i386/boot/edd.S +++ b/arch/i386/boot/edd.S @@ -15,42 +15,95 @@ #include <asm/setup.h> #if defined(CONFIG_EDD) || defined(CONFIG_EDD_MODULE) + +# It is assumed that %ds == INITSEG here + movb $0, (EDD_MBR_SIG_NR_BUF) movb $0, (EDDNR) -# Check the command line for two options: +# Check the command line for options: # edd=of disables EDD completely (edd=off) # edd=sk skips the MBR test (edd=skipmbr) +# edd=on re-enables EDD (edd=on) + pushl %esi - cmpl $0, %cs:cmd_line_ptr - jz done_cl + movw $edd_mbr_sig_start, %di # Default to edd=on + movl %cs:(cmd_line_ptr), %esi -# ds:esi has the pointer to the command line now - movl $(COMMAND_LINE_SIZE-7), %ecx -# loop through kernel command line one byte at a time -cl_loop: - cmpl $EDD_CL_EQUALS, (%si) + andl %esi, %esi + jz old_cl # Old boot protocol? + +# Convert to a real-mode pointer in fs:si + movl %esi, %eax + shrl $4, %eax + movw %ax, %fs + andw $0xf, %si + jmp have_cl_pointer + +# 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 + +# fs:si has the pointer to the command line now +have_cl_pointer: + +# Loop through kernel command line one byte at a time. Just in +# case the loader is buggy and failed to null-terminate the command line +# terminate if we get close enough to the end of the segment that we +# cannot fit "edd=XX"... +cl_atspace: + cmpw $-5, %si # Watch for segment wraparound + jae done_cl + movl %fs:(%si), %eax + andb %al, %al # End of line? + jz done_cl + cmpl $EDD_CL_EQUALS, %eax jz found_edd_equals - incl %esi - loop cl_loop - jmp done_cl + cmpb $0x20, %al # <= space consider whitespace + ja cl_skipword + incw %si + jmp cl_atspace + +cl_skipword: + cmpw $-5, %si # Watch for segment wraparound + jae done_cl + movb %fs:(%si), %al # End of string? + andb %al, %al + jz done_cl + cmpb $0x20, %al + jbe cl_atspace + incw %si + jmp cl_skipword + found_edd_equals: # only looking at first two characters after equals - addl $4, %esi - cmpw $EDD_CL_OFF, (%si) # edd=of - jz do_edd_off - cmpw $EDD_CL_SKIP, (%si) # edd=sk - jz do_edd_skipmbr - jmp done_cl +# late overrides early on the command line, so keep going after finding something + movw %fs:4(%si), %ax + cmpw $EDD_CL_OFF, %ax # edd=of + je do_edd_off + cmpw $EDD_CL_SKIP, %ax # edd=sk + je do_edd_skipmbr + cmpw $EDD_CL_ON, %ax # edd=on + je do_edd_on + jmp cl_skipword do_edd_skipmbr: - popl %esi - jmp edd_start + movw $edd_start, %di + jmp cl_skipword do_edd_off: - popl %esi - jmp edd_done + movw $edd_done, %di + jmp cl_skipword +do_edd_on: + movw $edd_mbr_sig_start, %di + jmp cl_skipword + done_cl: popl %esi - + jmpw *%di # Read the first sector of each BIOS disk device and store the 4-byte signature edd_mbr_sig_start: |
