[Qemu-devel] [Bug 1349277] Re: AArch64 emulation ignores SPSel=0 when taking (or returning from) an exception at EL1 or greater

[Andy Whitcroft]

** Also affects: qemu (Ubuntu)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1349277

Title:
  AArch64 emulation ignores SPSel=0 when taking (or returning from) an
  exception at EL1 or greater

Status in QEMU:
  New
Status in qemu package in Ubuntu:
  New

Bug description:
  The AArch64 emulation ignores SPSel=0 when:

  (1) taking an interrupt from an exception level greater than EL0
  (e.g., EL1t),

  (2) returning from an exception (via ERET) to an exception level
  greater than EL0 (e.g., EL1t), with SPSR_ELx[SPSel]=0.

  The attached patch fixes the problem in my application.

  Background:

  I'm running a standalone application (toy OS) that is performing
  preemptive multithreading between threads running at EL1t, with
  exception handling / context switching occurring at EL1h.  This bug
  causes the stack pointer to be corrupted in the threads running at
  EL1t (they end up with a version of the EL1h stack pointer (SP_EL1)).

  Occurs in:
        qemu-2.1.0-rc1 (found in)
        commit c60a57ff497667780132a3fcdc1500c83af5d5c0 (current master)

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