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[Qemu-devel] [Bug 1463338] Re: qemu-system-arm injects #UND exception wi

From: Peter Maydell
Subject: [Qemu-devel] [Bug 1463338] Re: qemu-system-arm injects #UND exception with wrong PC
Date: Mon, 20 Jun 2016 15:55:53 -0000

Should be in 2.6.

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

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  qemu-system-arm injects #UND exception with wrong PC

Status in QEMU:
  Fix Released

Bug description:
  Usually all accesses to coprocessor registers are only possible in PL1
  or higher. When accessing a coprocessor register in user mode, QEMU
  generates a trap and the PC of the trapping instruction is passed to
  the OS with an offset of+ 4. Some coprocessor registers can be
  configured to allow access to them in usermode (PL0). The latest qemu-
  git (ee09f84e6bf5383a23c9624115c26b72aa1e076c) seems to add an offest
  of 8 instead of four if such a register is accessed from user mode.
  This happens only if the coprocessors register that is accessed might
  also be accessed from PL0. In case all accesses to the coprocessor
  register from PL0 cause a trap, qemu injects the #UND trap with the
  correct PC value.

  Attached is a small test program that installs a signal handler for
  "SIGILL". On a pandaboard the progam prints "Val=0x2 Val2=0x2" whereas
  on the latest "qemu-system-arm" the output is : "Val=0x1 Val2=0x2"

  Qemu was configured with: "./configure --python=`which python2.7` 
  The test can be compiled with: "gcc -g -static test2.c -o test2"

  If further information is needed, feel free to ask.



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