[Qemu-devel] [Bug 1652373] [NEW] User-mode QEMU is not deterministic

[Lluís Vilanova]

Public bug reported:

QEMU in user-mode (linux-user or bsd-user) has no way to get the
equivalent of the "-icount" argument found in softmmu mode.

It is true that some system calls in user-mode can prevent deterministic
execution, but it would be very simple to patch time-related syscalls to
return a number based on icount when in deterministic mode.

Putting both changes together (icount + time-related syscalls) would
cover the needs for deterministic execution of most benchmarks (i.e.,
those not interacting with the network or other programs in the system).

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1652373

Title:
  User-mode QEMU is not deterministic

Status in QEMU:
  New

Bug description:
  QEMU in user-mode (linux-user or bsd-user) has no way to get the
  equivalent of the "-icount" argument found in softmmu mode.

  It is true that some system calls in user-mode can prevent
  deterministic execution, but it would be very simple to patch time-
  related syscalls to return a number based on icount when in
  deterministic mode.

  Putting both changes together (icount + time-related syscalls) would
  cover the needs for deterministic execution of most benchmarks (i.e.,
  those not interacting with the network or other programs in the
  system).

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