Re: [PATCH COMMITTED] Do not require memset elimination in explicit_bzero test

[Stefan Liebler <stli at linux dot vnet dot ibm dot com>]

On 12/30/2016 01:16 PM, Florian Weimer wrote:
> On 12/21/2016 07:04 PM, Florian Weimer wrote:
> > On 12/20/2016 11:09 AM, Florian Weimer wrote:
> > > Some targets fail to apply dead store elimination to the
> > > memset call in setup_ordinary_clear.  Before this commit,
> > > this causes the test case to fail.  Instead, the test case
> > > now logs lack of memset elimination as an informational
> > > message.
> > >
> > > 2016-12-20  Florian Weimer  <fweimer@redhat.com>
> > >
> > >     Do not require memset elimination in explicit_bzero test.
> > >     * string/tst-xbzero-opt.c (prepare_test_buffer): Force inlining.
> > >     (enum test_expectation): Add NO_EXPECTATIONS.
> > >     (subtests): NO_EXPECTATIONS for ordinary clear.
> > >     (check_test_buffer): Handle NO_EXPECTATIONS.
> > >     * string/Makefile (CFLAGS-tst-xbzero-opt.c): Compile with -O3.
> >
> > Stefan, this test still fails for me on s390x:
> >
> > PASS: no clear/prepare: expected 32 got 32
> > PASS: no clear/test: expected some got 32
> > PASS: ordinary clear/prepare: expected 32 got 32
> > INFO: ordinary clear/test: found 0 patterns (memset not eliminated)
> > PASS: explicit clear/prepare: expected 32 got 32
> > FAIL: explicit clear/test: expected 0 got 1
> >
> > Do you have an idea what's going on there?
>
> I filed bug 21006 and will add it as a release blocker.
>
> Thanks,
> Florian
Hi Florian,

the test is also failing on my system and I've had a look into it.

In setup_explicit_clear, the buffer is filled with the test_pattern.
On s390x the memcpy in prepare_test_buffer is done by loading
r4 / r5 with the test_pattern and using store multiple instruction
to store r4 / r5 to buf.
If explicit_bzero is resolved in setup_explicit_clear, r4 / r5 is
stored to stack by _dl_runtime_resolve and the call to memmem in
count_test_patterns finds a hit of the test_pattern on the stack.

The attached patch resolves all symbols at program startup by linking
with -z now.  This omits the call of _dl_runtime_resolve within
setup_explicit_clear and the test passes.

If this is okay, I'll commit this patch and clear this bug in the 
release blockers list in the release-wiki.

Bye
Stefan

ChangeLog:

	[BZ #21006]
	* string/Makefile (LDFLAGS-tst-xbzero-opt): New variable.

commit a07f447fd235d1898a56af7317a4ff6a11a603b9
Author: Stefan Liebler <stli@linux.vnet.ibm.com>
Date:   Tue Jan 10 08:47:13 2017 +0100

    S390: Fix FAIL in test string/tst-xbzero-opt [BZ #21006]
    
    On s390x this test failed with:
    FAIL: explicit clear/test: expected 0 got 1
    
    In setup_explicit_clear, the buffer is filled with the test_pattern.
    On s390x the memcpy in prepare_test_buffer is done by loading
    r4 / r5 with the test_pattern and using store multiple instruction
    to store r4 / r5 to buf.
    If explicit_bzero is resolved in setup_explicit_clear, r4 / r5 is
    stored to stack by _dl_runtime_resolve and the call to memmem in
    count_test_patterns finds a hit of the test_pattern on the stack.
    
    This patch resolves all symbols at program startup by linking with
    -z now.  This omits the call of _dl_runtime_resolve within
    setup_explicit_clear and the test passes.
    
    ChangeLog:
    
    	[BZ #21006]
    	* string/Makefile (LDFLAGS-tst-xbzero-opt): New variable.

diff --git a/string/Makefile b/string/Makefile
index 04e9da9..87e0d1d 100644
--- a/string/Makefile
+++ b/string/Makefile
@@ -73,6 +73,14 @@ CFLAGS-stratcliff.c = -fno-builtin
 CFLAGS-test-ffs.c = -fno-builtin
 CFLAGS-tst-inlcall.c = -fno-builtin
 CFLAGS-tst-xbzero-opt.c = -O3
+# BZ 21006: Resolve all functions but at least explicit_bzero at startup.
+# Otherwise the test fails on s390x as the memcpy in prepare_test_buffer is
+# done by loading r4 / r5 with the test_pattern and using store multiple
+# instruction to store r4 / r5 to buf.  If explicit_bzero would be resolved in
+# setup_explicit_clear, r4 / r5 would be stored to stack by _dl_runtime_resolve
+# and the call to memmem in count_test_patterns will find a hit of the
+# test_pattern on the stack.
+LDFLAGS-tst-xbzero-opt = -z now
 
 # Called during TLS initialization.
 CFLAGS-memcpy.c = $(no-stack-protector)