x86-64: Don't set GLRO(dl_platform) to NULL [BZ #22299]

Since ld.so expands $PLATFORM with GLRO(dl_platform), don't set
GLRO(dl_platform) to NULL.

	[BZ #22299]
	* sysdeps/x86/cpu-features.c (init_cpu_features): Don't set
	GLRO(dl_platform) to NULL.
	* sysdeps/x86_64/Makefile (tests): Add tst-platform-1.
	(modules-names): Add tst-platformmod-1 and
	x86_64/tst-platformmod-2.
	(CFLAGS-tst-platform-1.c): New.
	(CFLAGS-tst-platformmod-1.c): Likewise.
	(CFLAGS-tst-platformmod-2.c): Likewise.
	(LDFLAGS-tst-platformmod-2.so): Likewise.
	($(objpfx)tst-platform-1): Likewise.
	($(objpfx)tst-platform-1.out): Likewise.
	(tst-platform-1-ENV): Likewise.
	($(objpfx)x86_64/tst-platformmod-2.os): Likewise.
	* sysdeps/x86_64/tst-platform-1.c: New file.
	* sysdeps/x86_64/tst-platformmod-1.c: Likewise.
	* sysdeps/x86_64/tst-platformmod-2.c: Likewise.

5 files changed, 103 insertions, 4 deletions

diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index c267f17b76..332b0f0d4a 100644
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -335,7 +335,6 @@ no_cpuid:
 #endif
 
   /* Reuse dl_platform, dl_hwcap and dl_hwcap_mask for x86.  */
-  GLRO(dl_platform) = NULL;
 #if !HAVE_TUNABLES && defined SHARED
   /* The glibc.tune.hwcap_mask tunable is initialized already, so no need to do
      this.  */
@@ -346,13 +345,15 @@ no_cpuid:
   GLRO(dl_hwcap) = HWCAP_X86_64;
   if (cpu_features->kind == arch_kind_intel)
     {
+      const char *platform = NULL;
+
       if (CPU_FEATURES_ARCH_P (cpu_features, AVX512F_Usable)
 	  && CPU_FEATURES_CPU_P (cpu_features, AVX512CD))
 	{
 	  if (CPU_FEATURES_CPU_P (cpu_features, AVX512ER))
 	    {
 	      if (CPU_FEATURES_CPU_P (cpu_features, AVX512PF))
-		GLRO(dl_platform) = "xeon_phi";
+		platform = "xeon_phi";
 	    }
 	  else
 	    {
@@ -363,7 +364,7 @@ no_cpuid:
 	    }
 	}
 
-      if (GLRO(dl_platform) == NULL
+      if (platform == NULL
 	  && CPU_FEATURES_ARCH_P (cpu_features, AVX2_Usable)
 	  && CPU_FEATURES_ARCH_P (cpu_features, FMA_Usable)
 	  && CPU_FEATURES_CPU_P (cpu_features, BMI1)
@@ -371,7 +372,10 @@ no_cpuid:
 	  && CPU_FEATURES_CPU_P (cpu_features, LZCNT)
 	  && CPU_FEATURES_CPU_P (cpu_features, MOVBE)
 	  && CPU_FEATURES_CPU_P (cpu_features, POPCNT))
-	GLRO(dl_platform) = "haswell";
+	platform = "haswell";
+
+      if (platform != NULL)
+	GLRO(dl_platform) = platform;
     }
 #else
   GLRO(dl_hwcap) = 0;
diff --git a/sysdeps/x86_64/Makefile b/sysdeps/x86_64/Makefile
index 1514805f4a..12d4737240 100644
--- a/sysdeps/x86_64/Makefile
+++ b/sysdeps/x86_64/Makefile
@@ -58,6 +58,21 @@ LDFLAGS-tst-x86_64mod-1.so = -Wl,-soname,tst-x86_64mod-1.so
 
 $(objpfx)tst-x86_64-1: $(objpfx)x86_64/tst-x86_64mod-1.so
 
+ifneq (no,$(have-tunables))
+tests += tst-platform-1
+modules-names += tst-platformmod-1 x86_64/tst-platformmod-2
+CFLAGS-tst-platform-1.c = -mno-avx
+CFLAGS-tst-platformmod-1.c = -mno-avx
+CFLAGS-tst-platformmod-2.c = -mno-avx
+LDFLAGS-tst-platformmod-2.so = -Wl,-soname,tst-platformmod-2.so
+$(objpfx)tst-platform-1: $(objpfx)tst-platformmod-1.so
+$(objpfx)tst-platform-1.out: $(objpfx)x86_64/tst-platformmod-2.so
+# Turn off AVX512F_Usable and AVX2_Usable so that GLRO(dl_platform) is
+# always set to x86_64.
+tst-platform-1-ENV = LD_PRELOAD=$(objpfx)\$$PLATFORM/tst-platformmod-2.so \
+	GLIBC_TUNABLES=glibc.tune.hwcaps=-AVX512F_Usable,-AVX2_Usable
+endif
+
 tests += tst-audit3 tst-audit4 tst-audit5 tst-audit6 tst-audit7 \
 	 tst-audit10 tst-sse tst-avx tst-avx512
 test-extras += tst-audit4-aux tst-audit10-aux \
@@ -141,3 +156,8 @@ do-tests-clean common-mostlyclean: tst-x86_64-1-clean
 .PHONY: tst-x86_64-1-clean
 tst-x86_64-1-clean:
 	-rm -rf $(objpfx)x86_64
+
+$(objpfx)x86_64/tst-platformmod-2.os: $(objpfx)tst-platformmod-2.os
+	$(make-target-directory)
+	rm -f $@
+	ln $< $@
diff --git a/sysdeps/x86_64/tst-platform-1.c b/sysdeps/x86_64/tst-platform-1.c
new file mode 100644
index 0000000000..76a02e4b6d
--- /dev/null
+++ b/sysdeps/x86_64/tst-platform-1.c
@@ -0,0 +1,29 @@
+/* Test PRELOAD with $PLATFORM.
+   Copyright (C) 2017 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 <stdlib.h>
+
+extern int preload (void);
+
+static int
+do_test (void)
+{
+  return preload () == 0x1234 ? EXIT_SUCCESS : EXIT_FAILURE;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/x86_64/tst-platformmod-1.c b/sysdeps/x86_64/tst-platformmod-1.c
new file mode 100644
index 0000000000..9ef5e2b5be
--- /dev/null
+++ b/sysdeps/x86_64/tst-platformmod-1.c
@@ -0,0 +1,23 @@
+/* Test PRELOAD with $PLATFORM.
+   Copyright (C) 2017 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/>.  */
+
+int
+preload (void)
+{
+  return 0;
+}
diff --git a/sysdeps/x86_64/tst-platformmod-2.c b/sysdeps/x86_64/tst-platformmod-2.c
new file mode 100644
index 0000000000..d0e5103892
--- /dev/null
+++ b/sysdeps/x86_64/tst-platformmod-2.c
@@ -0,0 +1,23 @@
+/* Test PRELOAD with $PLATFORM.
+   Copyright (C) 2017 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/>.  */
+
+int
+preload (void)
+{
+  return 0x1234;
+}