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Trivial Change (E820map) : arch/i386/boot/setup.S

DISCUSSION Romit Dasgupta 2 participants 2 messages Jul 16, 2003

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Romit Dasgupta

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#0 lore raw

Hi,

     After reading the e820 method from Ralf Brown's interrupt list(

http://www.ctyme.com/intr/rb-1741.htm)
it seems that the es register wont get thrashed. So there is no need to repatedly execute (for getting each map entry) the following two lines inside jmpe820: of seutp.S and thus can be moved out as below. Is there any reason to do it inside?

pushw %ds
popw %es

jmpe820:

       movl    $0x0000e820, %eax               # e820, upper word zeroed
       movl    $SMAP, %edx                     # ascii 'SMAP'
       movl    $20, %ecx                       # size of the e820rec
#       pushw   %ds                             # data record.
#       popw    %es

Diff
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===== setup.S 1.22 vs edited =====
318a319,320

Quoted 2 lines

pushw %ds
popw %es

324,325c326,327

<       pushw   %ds                             # data record.
<       popw    %es

---

Quoted 2 lines

# pushw %ds # data record.
# popw %es

1156d1157
<

Tested in my i386 machine and here is the relevant portion of dmesg after boot.

Quoted 5 lines

Linux version 2.6.0-test1 (root@feynman) (gcc version 3.2 20020903 (Red Hat Linux 8.0 3.2-7)) #14 Thu Jul 17 01:05:15 SGT 2003 Video mode to be used for restore is f00
BIOS-provided physical RAM map:
BIOS-e820: 0000000000000000 - 000000000009f800 (usable)
BIOS-e820: 000000000009f800 - 00000000000a0000 (reserved)

Quoted 8 lines

BIOS-e820: 00000000000e0000 - 0000000000100000 (reserved)
BIOS-e820: 0000000000100000 - 0000000017ff0000 (usable)
BIOS-e820: 0000000017ff0000 - 0000000017ffec00 (ACPI data)
BIOS-e820: 0000000017ffec00 - 0000000018000000 (ACPI NVS)
BIOS-e820: 00000000fff80000 - 0000000100000000 (reserved)
0MB HIGHMEM available.
383MB LOWMEM available.
On node 0 totalpages: 98288

Regards,
-Romit

#1 lore raw
Quoted 7 lines · Romit Dasgupta

Hi,

      After reading the e820 method from Ralf Brown's interrupt list(

http://www.ctyme.com/intr/rb-1741.htm)
it seems that the es register wont get thrashed. So there is no need to repatedly execute (for getting each map entry) the following two lines inside jmpe820: of seutp.S and thus can be moved out as below. Is there any reason to do it inside?

Yes - BIOSes and the specification are only distant relatives. We get all sorts of fun from them - 0 sized regions, system ROM reported as RAM, E801 returns in the wrong registers and so on