[Qemu-devel] [Bug 1783437] [NEW] read-modify-write page faults error code has write bit unset

[Fabian Hemmer]

Public bug reported:

Consider the attached C file, which does a read-modify-write of the form
`add [mem], reg`, where `mem` points to a non-present page. In the
resulting page fault, the W/R bit is not set, while real hardware does
set this bit.

% gcc -m32 qemu-bug1.c&& ./a.out && qemu-i386 ./a.out
page fault: addr=0x70000000 err=0x6
page fault: addr=0x70000000 err=0x4

Tested on the qemu-3.0.0-rc1 release.

** Affects: qemu
     Importance: Undecided
         Status: New

** Attachment added: "qemu-bug1.c"
   
https://bugs.launchpad.net/bugs/1783437/+attachment/5167345/+files/qemu-bug1.c

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https://bugs.launchpad.net/bugs/1783437

Title:
  read-modify-write page faults error code has write bit unset

Status in QEMU:
  New

Bug description:
  Consider the attached C file, which does a read-modify-write of the
  form `add [mem], reg`, where `mem` points to a non-present page. In
  the resulting page fault, the W/R bit is not set, while real hardware
  does set this bit.

  % gcc -m32 qemu-bug1.c&& ./a.out && qemu-i386 ./a.out
  page fault: addr=0x70000000 err=0x6
  page fault: addr=0x70000000 err=0x4

  Tested on the qemu-3.0.0-rc1 release.

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