[Qemu-devel] [PATCH 0/7] target-ppc/linux-user: NPTL support

[Nathan Froyd]

This patch series adds NPTL support in Linux user-mode emulation to
32-bit PowerPC targets.

The main complication comes from implementing atomic instructions
properly.  We chose to implement a simplistic model:

- reserved loads record the value loaded;

- conditional stores check that the memory at the effective address
  contains the value loaded by the previous reserved load, in addition
  to all other checks.  if so, the store succeeds; otherwise, it fails.

It is possible to implement something more sophisticated using mprotect:

- reserved loads write-protect the page from which the value is loaded;

- regular stores to the page (through SIGSEGV handling) remove the write
  protection (which is roughly how the architecture really works);

- conditional stores fail if the page was not write-protected, in
  addition to all other checks.  If the store succeeds, then the page is
  unprotected.

but the simple scheme works well enough and should be somewhat faster.
The simple scheme is what's already done for system mode, too; it's even
slightly dumber in system mode because we don't check for equality of
values.

The patch series has been tested against the glibc testsuite, where it
passes a good chunk (90%+) of the testsuite.  The other 10% are
basically things that are not going to work in QEMU anytime soon
(e.g. sharing futexes between multiple processes, using clone(2)
directly, etc.).  I should note that proper testing requires a patch to
use a correct exit status for uncaught signals; such a patch has been
posted to this list before by Riku Voipio.  (I have a different local
version that I used instead.)  Testing with recent glibc also requires
adding support for private futexes and a few other futex operations;
again, a patch for this has been posted by Riku and I used a slightly
different local version.

-Nathan

Nathan Froyd (7):
  linux-user: initialize mmap_mutex properly
  target-ppc: fix cpu_clone_regs
  target-ppc: add cpu_set_tls
  target-ppc: retain l{w,d}arx loaded value
  target-ppc: add exceptions for conditional stores
  linux-user: handle POWERPC_EXCP_STCX
  enable NPTL for ppc-linux-user targets in configure

 configure              |    2 +
 linux-user/main.c      |   68 ++++++++++++++++++++++++++++++++++++++
 linux-user/mmap.c      |    2 +-
 target-ppc/cpu.h       |   24 +++++++++++--
 target-ppc/helper.c    |    2 +-
 target-ppc/machine.c   |    4 +-
 target-ppc/op_helper.c |    4 +-
 target-ppc/translate.c |   84 ++++++++++++++++++++++++++++++++++--------------
 8 files changed, 156 insertions(+), 34 deletions(-)