[Qemu-devel] [Bug 995758] [NEW] Possibly inaccurate statement in PC Platform Docs

[Qemu-devel] [Bug 995758] [NEW] Possibly inaccurate statement in PC Platform Docs

[Graham Cottrell]

Public bug reported:

The documentation at:

http://wiki.qemu.org/Documentation/Platforms/PC

Contains the statement that the processor, after reset, executes code
starting from address 0xFFFFF, corresponding to the last byte of the
single megabyte of memory in the old 8086 address range.

>From my recollection of working in the microcomputer industry in the
late 1980's, execution actually starts in real mode at the start of the
last 16 bytes of addressable memory, at 0xFFFF0.  Think about it - if
it's the last byte there's no room for an address operand to accompany a
1-byte opcode.

** Affects: qemu
     Importance: Undecided
         Status: New

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Title:
  Possibly inaccurate statement in PC Platform Docs

Status in QEMU:
  New

Bug description:
  The documentation at:

  http://wiki.qemu.org/Documentation/Platforms/PC

  Contains the statement that the processor, after reset, executes code
  starting from address 0xFFFFF, corresponding to the last byte of the
  single megabyte of memory in the old 8086 address range.

  From my recollection of working in the microcomputer industry in the
  late 1980's, execution actually starts in real mode at the start of
  the last 16 bytes of addressable memory, at 0xFFFF0.  Think about it -
  if it's the last byte there's no room for an address operand to
  accompany a 1-byte opcode.

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[Qemu-devel] [Bug 995758] Re: Possibly inaccurate statement in PC Platform Docs

[Graham Cottrell]

Oh, and if I recall correctly, on the 80286 and 80386 and 80486, on
reset the amount of addressable memory was 16MiB, 4GiB and 4GiB
respectively, and IBM made the choice to map the BIOS ROMs to both the
top of addressable memory and at the top of the first MiB.  The CPU's
themselves always reset to near the top of their address range, and the
BIOS writers promptly jumped back down to somewhere near the top of the
first MiB.

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https://bugs.launchpad.net/bugs/995758

Title:
  Possibly inaccurate statement in PC Platform Docs

Status in QEMU:
  New

Bug description:
  The documentation at:

  http://wiki.qemu.org/Documentation/Platforms/PC

  Contains the statement that the processor, after reset, executes code
  starting from address 0xFFFFF, corresponding to the last byte of the
  single megabyte of memory in the old 8086 address range.

  From my recollection of working in the microcomputer industry in the
  late 1980's, execution actually starts in real mode at the start of
  the last 16 bytes of addressable memory, at 0xFFFF0.  Think about it -
  if it's the last byte there's no room for an address operand to
  accompany a 1-byte opcode.

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[Qemu-devel] [Bug 995758] Re: Possibly inaccurate statement in PC Platform Docs

[Thomas Huth]

As far as I can see, the wording on the page only says that the BIOS
ends at address 0xFFFFF, not that it starts execution at exactly that
address. So I think that page is ok.

** Changed in: qemu
       Status: New => Invalid

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https://bugs.launchpad.net/bugs/995758

Title:
  Possibly inaccurate statement in PC Platform Docs

Status in QEMU:
  Fix Released

Bug description:
  The documentation at:

  http://wiki.qemu.org/Documentation/Platforms/PC

  Contains the statement that the processor, after reset, executes code
  starting from address 0xFFFFF, corresponding to the last byte of the
  single megabyte of memory in the old 8086 address range.

  From my recollection of working in the microcomputer industry in the
  late 1980's, execution actually starts in real mode at the start of
  the last 16 bytes of addressable memory, at 0xFFFF0.  Think about it -
  if it's the last byte there's no room for an address operand to
  accompany a 1-byte opcode.

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[Qemu-devel] [Bug 995758] Re: Possibly inaccurate statement in PC Platform Docs

[Thomas Huth]

OK, I just read the text again, and the sentences before the one with
the 0xfffff indeed sounded like the the start address was at the last
byte. I've reworded the text now a little bit so that it should be more
accurate.

** Changed in: qemu
       Status: Invalid => Fix Released

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/995758

Title:
  Possibly inaccurate statement in PC Platform Docs

Status in QEMU:
  Fix Released

Bug description:
  The documentation at:

  http://wiki.qemu.org/Documentation/Platforms/PC

  Contains the statement that the processor, after reset, executes code
  starting from address 0xFFFFF, corresponding to the last byte of the
  single megabyte of memory in the old 8086 address range.

  From my recollection of working in the microcomputer industry in the
  late 1980's, execution actually starts in real mode at the start of
  the last 16 bytes of addressable memory, at 0xFFFF0.  Think about it -
  if it's the last byte there's no room for an address operand to
  accompany a 1-byte opcode.

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/995758/+subscriptions