.travis.yml: skip ppc64abi32-linux-user with plugins

We actually see failures on threadcount running without plugins:

  retry.py -n 1000 -c -- \
    ./ppc64abi32-linux-user/qemu-ppc64abi32 \
    ./tests/tcg/ppc64abi32-linux-user/threadcount

which reports:

  0: 978 times (97.80%), avg time 0.270 (0.01 varience/0.08 deviation)
  -6: 21 times (2.10%), avg time 0.336 (0.01 varience/0.12 deviation)
  -11: 1 times (0.10%), avg time 0.502 (0.00 varience/0.00 deviation)
  Ran command 1000 times, 978 passes

But when running with plugins we hit the failure a lot more often:

  0: 91 times (91.00%), avg time 0.302 (0.04 varience/0.19 deviation)
  -11: 9 times (9.00%), avg time 0.558 (0.01 varience/0.11 deviation)
  Ran command 100 times, 91 passes

The crash occurs in guest code which is the same in both pass and fail
cases. However we see various messages reported on the console about
corrupted memory lists which seems to imply the guest memory allocation
is corrupted. This lines up with the seg fault being in the guest
__libc_free function. So we think this is a guest bug which is
exacerbated by various modes of translation. If anyone has access to
real hardware to soak test the test case we could prove this properly.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20200714175516.5475-1-alex.bennee@linaro.org>

.travis.yml

@@ -350,9 +350,10 @@ jobs:
     # Run check-tcg against linux-user (with plugins)
     # we skip sparc64-linux-user until it has been fixed somewhat
     # we skip cris-linux-user as it doesn't use the common run loop
+    # we skip ppc64abi32-linux-user as it seems to have a broken libc
     - name: "GCC plugins check-tcg (user)"
       env:
-        - CONFIG="--disable-system --enable-plugins --enable-debug-tcg --target-list-exclude=sparc64-linux-user,cris-linux-user"
+        - CONFIG="--disable-system --enable-plugins --enable-debug-tcg --target-list-exclude=sparc64-linux-user,cris-linux-user,ppc64abi32-linux-user"
         - TEST_BUILD_CMD="make build-tcg"
         - TEST_CMD="make check-tcg"
         - CACHE_NAME="${TRAVIS_BRANCH}-linux-gcc-debug-tcg"