tunables: Use glibc.tune.hwcap_mask tunable instead of _dl_hwcap_mask

Drop _dl_hwcap_mask when building with tunables.  This completes the
transition of hwcap_mask reading from _dl_hwcap_mask to tunables.

	* elf/dl-hwcaps.h: New file.
	* elf/dl-hwcaps.c: Include it.
	(_dl_important_hwcaps)[HAVE_TUNABLES]: Read and update
	glibc.tune.hwcap_mask.
	* elf/dl-cache.c: Include dl-hwcaps.h.
	(_dl_load_cache_lookup)[HAVE_TUNABLES]: Read
	glibc.tune.hwcap_mask.
	* sysdeps/sparc/sparc32/dl-machine.h: Likewise.
	* elf/dl-support.c (_dl_hwcap2)[HAVE_TUNABLES]: Drop
	_dl_hwcap_mask.
	* elf/rtld.c (rtld_global_ro)[HAVE_TUNABLES]: Drop
	_dl_hwcap_mask.
	(process_envvars)[HAVE_TUNABLES]: Likewise.
	* sysdeps/generic/ldsodefs.h (rtld_global_ro)[HAVE_TUNABLES]:
	Likewise.
	* sysdeps/x86/cpu-features.c (init_cpu_features): Don't
	initialize dl_hwcap_mask when tunables are enabled.

ChangeLog

@@ -1,5 +1,23 @@
 2017-06-07  Siddhesh Poyarekar  <siddhesh@sourceware.org>
 
+	* elf/dl-hwcaps.h: New file.
+	* elf/dl-hwcaps.c: Include it.
+	(_dl_important_hwcaps)[HAVE_TUNABLES]: Read and update
+	glibc.tune.hwcap_mask.
+	* elf/dl-cache.c: Include dl-hwcaps.h.
+	(_dl_load_cache_lookup)[HAVE_TUNABLES]: Read
+	glibc.tune.hwcap_mask.
+	* sysdeps/sparc/sparc32/dl-machine.h: Likewise.
+	* elf/dl-support.c (_dl_hwcap2)[HAVE_TUNABLES]: Drop
+	_dl_hwcap_mask.
+	* elf/rtld.c (rtld_global_ro)[HAVE_TUNABLES]: Drop
+	_dl_hwcap_mask.
+	(process_envvars)[HAVE_TUNABLES]: Likewise.
+	* sysdeps/generic/ldsodefs.h (rtld_global_ro)[HAVE_TUNABLES]:
+	Likewise.
+	* sysdeps/x86/cpu-features.c (init_cpu_features): Don't
+	initialize dl_hwcap_mask when tunables are enabled.
+
 	* sysdeps/unix/sysv/linux/i386/dl-procinfo.h: Add include
 	guard.
 	* sysdeps/unix/sysv/linux/s390/dl-procinfo.h: Likewise.

elf/dl-cache.c

@@ -24,6 +24,7 @@
 #include <dl-procinfo.h>
 #include <stdint.h>
 #include <_itoa.h>
+#include <dl-hwcaps.h>
 
 #ifndef _DL_PLATFORMS_COUNT
 # define _DL_PLATFORMS_COUNT 0
@@ -258,8 +259,10 @@ _dl_load_cache_lookup (const char *name)
       if (platform != (uint64_t) -1)
 	platform = 1ULL << platform;
 
+      uint64_t hwcap_mask = GET_HWCAP_MASK();
+
 #define _DL_HWCAP_TLS_MASK (1LL << 63)
-      uint64_t hwcap_exclude = ~((GLRO(dl_hwcap) & GLRO(dl_hwcap_mask))
+      uint64_t hwcap_exclude = ~((GLRO(dl_hwcap) & hwcap_mask)
 				 | _DL_HWCAP_PLATFORM | _DL_HWCAP_TLS_MASK);
 
       /* Only accept hwcap if it's for the right platform.  */

elf/dl-hwcaps.c

@@ -24,6 +24,7 @@
 #include <ldsodefs.h>
 
 #include <dl-procinfo.h>
+#include <dl-hwcaps.h>
 
 #ifdef _DL_FIRST_PLATFORM
 # define _DL_FIRST_EXTRA (_DL_FIRST_PLATFORM + _DL_PLATFORMS_COUNT)
@@ -37,8 +38,9 @@ internal_function
 _dl_important_hwcaps (const char *platform, size_t platform_len, size_t *sz,
 		      size_t *max_capstrlen)
 {
+  uint64_t hwcap_mask = GET_HWCAP_MASK();
   /* Determine how many important bits are set.  */
-  uint64_t masked = GLRO(dl_hwcap) & GLRO(dl_hwcap_mask);
+  uint64_t masked = GLRO(dl_hwcap) & hwcap_mask;
   size_t cnt = platform != NULL;
   size_t n, m;
   size_t total;
@@ -125,7 +127,12 @@ _dl_important_hwcaps (const char *platform, size_t platform_len, size_t *sz,
 	 LD_HWCAP_MASK environment variable (or default HWCAP_IMPORTANT).
 	 So there is no way to request ignoring an OS-supplied dsocap
 	 string and bit like you can ignore an OS-supplied HWCAP bit.  */
-      GLRO(dl_hwcap_mask) |= (uint64_t) mask << _DL_FIRST_EXTRA;
+      hwcap_mask |= (uint64_t) mask << _DL_FIRST_EXTRA;
+#if HAVE_TUNABLES
+      TUNABLE_SET (glibc, tune, hwcap_mask, uint64_t, hwcap_mask);
+#else
+      GLRO(dl_hwcap_mask) = hwcap_mask;
+#endif
       size_t len;
       for (const char *p = dsocaps; p < dsocaps + dsocapslen; p += len + 1)
 	{

elf/dl-hwcaps.h

@@ -0,0 +1,31 @@
+/* Hardware capability support for run-time dynamic loader.
+   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 <elf/dl-tunables.h>
+
+#ifdef SHARED
+# if HAVE_TUNABLES
+#  define GET_HWCAP_MASK() \
+  TUNABLE_GET (glibc, tune, hwcap_mask, uint64_t, NULL)
+# else
+#  define GET_HWCAP_MASK() GLRO(dl_hwcap_mask)
+# endif
+#else
+/* HWCAP_MASK is ignored in static binaries.  */
+# define GET_HWCAP_MASK() (0)
+#endif

elf/dl-support.c

@@ -164,6 +164,7 @@ uint64_t _dl_hwcap2 __attribute__ ((nocommon));
 /* The value of the FPU control word the kernel will preset in hardware.  */
 fpu_control_t _dl_fpu_control = _FPU_DEFAULT;
 
+#if !HAVE_TUNABLES
 /* This is not initialized to HWCAP_IMPORTANT, matching the definition
    of _dl_important_hwcaps, below, where no hwcap strings are ever
    used.  This mask is still used to mediate the lookups in the cache
@@ -171,6 +172,7 @@ fpu_control_t _dl_fpu_control = _FPU_DEFAULT;
    LD_HWCAP_MASK environment variable here), there is no real point in
    setting _dl_hwcap nonzero below, but we do anyway.  */
 uint64_t _dl_hwcap_mask __attribute__ ((nocommon));
+#endif
 
 /* Prevailing state of the stack.  Generally this includes PF_X, indicating it's
  * executable but this isn't true for all platforms.  */

elf/rtld.c

@@ -159,7 +159,9 @@ struct rtld_global_ro _rtld_global_ro attribute_relro =
     ._dl_debug_fd = STDERR_FILENO,
     ._dl_use_load_bias = -2,
     ._dl_correct_cache_id = _DL_CACHE_DEFAULT_ID,
+#if !HAVE_TUNABLES
     ._dl_hwcap_mask = HWCAP_IMPORTANT,
+#endif
     ._dl_lazy = 1,
     ._dl_fpu_control = _FPU_DEFAULT,
     ._dl_pagesize = EXEC_PAGESIZE,
@@ -2402,6 +2404,7 @@ process_envvars (enum mode *modep)
 	    _dl_show_auxv ();
 	  break;
 
+#if !HAVE_TUNABLES
 	case 10:
 	  /* Mask for the important hardware capabilities.  */
 	  if (!__libc_enable_secure
@@ -2409,6 +2412,7 @@ process_envvars (enum mode *modep)
 	    GLRO(dl_hwcap_mask) = __strtoul_internal (&envline[11], NULL,
 						      0, 0);
 	  break;
+#endif
 
 	case 11:
 	  /* Path where the binary is found.  */

sysdeps/generic/ldsodefs.h

@@ -515,8 +515,10 @@ struct rtld_global_ro
   /* Mask for hardware capabilities that are available.  */
   EXTERN uint64_t _dl_hwcap;
 
+#if !HAVE_TUNABLES
   /* Mask for important hardware capabilities we honour. */
   EXTERN uint64_t _dl_hwcap_mask;
+#endif
 
 #ifdef HAVE_AUX_VECTOR
   /* Pointer to the auxv list supplied to the program at startup.  */

sysdeps/sparc/sparc32/dl-machine.h

@@ -27,6 +27,7 @@
 #include <sysdep.h>
 #include <tls.h>
 #include <dl-plt.h>
+#include <elf/dl-hwcaps.h>
 
 /* Return nonzero iff ELF header is compatible with the running host.  */
 static inline int
@@ -37,7 +38,8 @@ elf_machine_matches_host (const Elf32_Ehdr *ehdr)
   else if (ehdr->e_machine == EM_SPARC32PLUS)
     {
 #ifdef SHARED
-      return GLRO(dl_hwcap) & GLRO(dl_hwcap_mask) & HWCAP_SPARC_V9;
+      uint64_t hwcap_mask = GET_HWCAP_MASK();
+      return GLRO(dl_hwcap) & hwcap_mask & HWCAP_SPARC_V9;
 #else
       return GLRO(dl_hwcap) & HWCAP_SPARC_V9;
 #endif

sysdeps/x86/cpu-features.c

@@ -316,7 +316,11 @@ no_cpuid:
   /* Reuse dl_platform, dl_hwcap and dl_hwcap_mask for x86.  */
   GLRO(dl_platform) = NULL;
   GLRO(dl_hwcap) = 0;
+#if !HAVE_TUNABLES
+  /* The glibc.tune.hwcap_mask tunable is initialized already, so no need to do
+     this.  */
   GLRO(dl_hwcap_mask) = HWCAP_IMPORTANT;
+#endif
 
 # ifdef __x86_64__
   if (cpu_features->kind == arch_kind_intel)