[COMMITTED] BZ#18383: Another test case, with TLS refs and defs in separate TUs.
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Message ID 20150602235638.52B7A2C3AB9@topped-with-meat.com
State New
Headers show

Commit Message

Roland McGrath June 2, 2015, 11:56 p.m. UTC
In investigating BZ#18383 (the elf/tst-tlsalign case) on ARM, I found that
it in fact appears to be an assembler bug.  That bug is only tickled by the
way GCC emits the references to the TLS variables when they are in the same
translation unit.  So this new test case (tst-tlsalign-extern) puts them in
a separate file.  On ARM, tst-tlsalign-extern works while tst-tlsalign
fails.  I think this demonstrates that libc is not actually buggy on ARM.

However, the original case still fails when statically linked on i?86 and
x86_64 (it crashes in early startup, which was never the ARM failure
mode)--and so does tst-tlsalign-extern-static.  So I think x86 has a bug
that is distinct from the ARM bug, though one of the same tests tickles
both bugs.

Since my current focus is on ARM, I'm going to report the ARM assembler bug
and not worry about this further for now.  It would be worthwhile for
someone to investigate the x86 bug, which is probably an actual libc bug.
(It affects only static linking and only an unusual usage pattern, so it's
not a high priority.)


Thanks,
Roland


2015-06-02  Roland McGrath  <roland@hack.frob.com>

	[BZ #18383]
	* elf/tst-tlsalign-extern.c: New file.
	* elf/tst-tlsalign-extern-static.c: New file.
	* elf/tst-tlsalign-vars.c: New file.
	* elf/Makefile (tests-static): Add tst-tlsalign-extern-static.
	[$(build-shared) = yes] (tests): Add tst-tlsalign-extern.
	($(objpfx)tst-tlsalign-extern): Depend on tst-tlsalign-vars.o.
	($(objpfx)tst-tlsalign-extern-static): Likewise.
	(test-xfail-tst-tlsalign-extern-static): New variable.

Patch
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diff --git a/elf/Makefile b/elf/Makefile
index dedf3c7..f2a115a 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -121,7 +121,8 @@  tests = tst-tls1 tst-tls2 tst-tls9 tst-leaks1 \
 	tst-auxv
 tests-static = tst-tls1-static tst-tls2-static tst-stackguard1-static \
 	       tst-leaks1-static tst-array1-static tst-array5-static \
-	       tst-ptrguard1-static tst-dl-iter-static tst-tlsalign-static
+	       tst-ptrguard1-static tst-dl-iter-static \
+	       tst-tlsalign-static tst-tlsalign-extern-static
 ifeq (yes,$(build-shared))
 tests-static += tst-tls9-static
 tst-tls9-static-ENV = \
@@ -146,7 +147,7 @@  tests += loadtest restest1 preloadtest loadfail multiload origtest resolvfail \
 	 tst-stackguard1 tst-addr1 tst-thrlock \
 	 tst-unique1 tst-unique2 $(if $(CXX),tst-unique3 tst-unique4) \
 	 tst-initorder tst-initorder2 tst-relsort1 tst-null-argv \
-	 tst-ptrguard1 tst-tlsalign
+	 tst-ptrguard1 tst-tlsalign tst-tlsalign-extern
 #	 reldep9
 ifeq ($(build-hardcoded-path-in-tests),yes)
 tests += tst-dlopen-aout
@@ -528,10 +529,16 @@  $(objpfx)tst-initorder: $(objpfx)tst-initordera4.so $(objpfx)tst-initordera1.so
 $(objpfx)tst-null-argv: $(objpfx)tst-null-argv-lib.so
 $(objpfx)tst-tlsalign: $(objpfx)tst-tlsalign-lib.so
 
-# BZ#18383: broken on at least ARM (both) and x86-64 (static only).
+# BZ#18383: broken on at least ARM (both) and i386/x86-64 (static only).
 test-xfail-tst-tlsalign = yes
 test-xfail-tst-tlsalign-static = yes
 
+$(objpfx)tst-tlsalign-extern: $(objpfx)tst-tlsalign-vars.o
+$(objpfx)tst-tlsalign-extern-static: $(objpfx)tst-tlsalign-vars.o
+
+# BZ#18383: broken on at least i386/x86-64 (static only).
+test-xfail-tst-tlsalign-extern-static = yes
+
 tst-null-argv-ENV = LD_DEBUG=all LD_DEBUG_OUTPUT=$(objpfx)tst-null-argv.debug.out
 LDFLAGS-nodel2mod3.so = $(no-as-needed)
 LDFLAGS-reldepmod5.so = $(no-as-needed)
diff --git a/elf/tst-tlsalign-extern-static.c b/elf/tst-tlsalign-extern-static.c
new file mode 100644
index 0000000..e84900e
--- /dev/null
+++ b/elf/tst-tlsalign-extern-static.c
@@ -0,0 +1 @@ 
+#include "tst-tlsalign-extern.c"
diff --git a/elf/tst-tlsalign-extern.c b/elf/tst-tlsalign-extern.c
new file mode 100644
index 0000000..661b671
--- /dev/null
+++ b/elf/tst-tlsalign-extern.c
@@ -0,0 +1,74 @@ 
+/* Test for large alignment in TLS blocks (extern case), BZ#18383.
+   Copyright (C) 2015 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+/* This is the same as tst-tlsalign-static.c, except that it uses
+   TLS variables that are defined in a separate translation unit
+   (ts-tlsalign-vars.c).  It turned out that the cause of BZ#18383
+   on ARM was actually an ARM assembler bug triggered by the ways of
+   using .tdata/.tbss sections and relocs referring to them that GCC
+   chooses when the variables are defined in the same translation
+   unit that contains the references.  */
+
+extern __thread int tdata1;
+extern __thread int tdata2;
+extern __thread int tdata3;
+extern __thread int tbss1;
+extern __thread int tbss2;
+extern __thread int tbss3;
+
+static int
+test_one (const char *which, unsigned int alignment, int *var, int value)
+{
+  uintptr_t addr = (uintptr_t) var;
+  unsigned int misalign = addr & (alignment - 1);
+
+  printf ("%s TLS address %p %% %u = %u\n",
+	  which, (void *) var, alignment, misalign);
+
+  int got = *var;
+  if (got != value)
+    {
+      printf ("%s value %d should be %d\n", which, got, value);
+      return 1;
+    }
+
+  return misalign != 0;
+}
+
+static int
+do_test (void)
+{
+  int fail = 0;
+
+  fail |= test_one ("tdata1", 4, &tdata1, 1);
+  fail |= test_one ("tdata2", 0x10, &tdata2, 2);
+  fail |= test_one ("tdata3", 0x1000, &tdata3, 4);
+
+  fail |= test_one ("tbss1", 4, &tbss1, 0);
+  fail |= test_one ("tbss2", 0x10, &tbss2, 0);
+  fail |= test_one ("tbss3", 0x1000, &tbss3, 0);
+
+  return fail ? EXIT_FAILURE : EXIT_SUCCESS;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/elf/tst-tlsalign-vars.c b/elf/tst-tlsalign-vars.c
new file mode 100644
index 0000000..01b3501
--- /dev/null
+++ b/elf/tst-tlsalign-vars.c
@@ -0,0 +1,28 @@ 
+/* This is for tst-tlsalign-extern.c, which see.  It's essential for the
+   purpose of the test that these definitions be in a separate translation
+   unit from the code using the variables.  */
+
+__thread int tdata1 = 1;
+__thread int tdata2 __attribute__ ((aligned (0x10))) = 2;
+__thread int tdata3 __attribute__ ((aligned (0x1000))) = 4;
+__thread int tbss1;
+__thread int tbss2 __attribute__ ((aligned (0x10)));
+__thread int tbss3 __attribute__ ((aligned (0x1000)));
+
+/* This function is never called.  But its presence in this translation
+   unit makes GCC emit the variables above in the order defined (perhaps
+   because it's the order in which they're used here?) rather than
+   reordering them into descending order of alignment requirement--and so
+   keeps it more similar to the tst-tlsalign-static.c case--just in case
+   that affects the bug (though there is no evidence that it does).  */
+
+void
+unused (void)
+{
+  tdata1 = -1;
+  tdata2 = -2;
+  tdata3 = -3;
+  tbss1 = -4;
+  tbss2 = -5;
+  tbss3 = -6;
+}