Fix static-binary lazy FPU context allocation

Long ago static startup did not parse the auxiliary vector and therefore
could not get at any `AT_FPUCW' tag to check whether upon FPU context
allocation the kernel would use a FPU control word setting different to
that provided by the `__fpu_control' variable.  Static startup therefore
always initialized the FPU control word, forcing immediate FPU context
allocation even for binaries that otherwise never used the FPU.

As from GIT commit f8f900ecb9096ec47f5b7bb7626e29223c69061a static
startup supports parsing the auxiliary vector, so now it can avoid
explicit initialization of the FPU control word, just as can dynamic
startup, in the usual case where the setting written to the FPU control
word would be the same as the kernel uses.  This defers FPU context
allocation until the binary itself actually pokes at the FPU.

Note that the `AT_FPUCW' tag is usually absent from the auxiliary vector
in which case _FPU_DEFAULT is assumed to be the kernel default.

8 files changed, 69 insertions, 11 deletions

diff --git a/ChangeLog b/ChangeLog
index 9b73de5..ae3a10c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,25 @@
+2013-09-09  Maciej W. Rozycki  <macro@codesourcery.com>
+
+	* csu/init-first.c (_init): Remove the !SHARED condition around
+	FPU control word initialization.
+	* elf/dl-support.c (_dl_fpu_control): New variable.
+	(_dl_aux_init) <AT_FPUCW>: Initialize it.
+	* math/test-fpucw.c [!FPU_CONTROL] (FPU_CONTROL): New macro.
+	(main): Replace _FPU_DEFAULT with FPU_CONTROL throughout.
+	* math/test-fpucw-static.c: New file.
+	* math/test-fpucw-ieee.c: New file.
+	* math/test-fpucw-ieee-static.c: New file.
+	* math/Makefile (tests): Add `test-fpucw-ieee' and
+	`$(tests-static)'.
+	(tests-static): New variable.
+	[($(build-shared),yes)] ($(addprefix $(objpfx),$(tests))): Move
+	dependency to...
+	[($(build-shared),yes)]
+	($(addprefix $(objpfx),$(filter-out $(tests-static),$(tests)))):
+	... this.
+	[($(build-shared),yes)] ($(addprefix $(objpfx),$(tests-static))):
+	New dependency.
+
 2013-09-09  Allan McRae  <allan@archlinux.org>
 
 	[BZ #15939]
diff --git a/csu/init-first.c b/csu/init-first.c
index f0ebc94..b4d22ce 100644
--- a/csu/init-first.c
+++ b/csu/init-first.c
@@ -61,11 +61,8 @@ _init (int argc, char **argv, char **envp)
   if (!__libc_multiple_libcs)
     {
       /* Set the FPU control word to the proper default value if the
-	 kernel would use a different value.  (In a static program we
-	 don't have this information.)  */
-#ifdef SHARED
+	 kernel would use a different value.  */
       if (__fpu_control != GLRO(dl_fpu_control))
-#endif
 	__setfpucw (__fpu_control);
     }
 
diff --git a/elf/dl-support.c b/elf/dl-support.c
index 5a082fe..2023bd0 100644
--- a/elf/dl-support.c
+++ b/elf/dl-support.c
@@ -167,6 +167,9 @@ size_t _dl_phnum;
 uint64_t _dl_hwcap __attribute__ ((nocommon));
 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;
+
 /* 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
@@ -253,6 +256,9 @@ _dl_aux_init (ElfW(auxv_t) *av)
       case AT_HWCAP2:
 	GLRO(dl_hwcap2) = (unsigned long int) av->a_un.a_val;
 	break;
+      case AT_FPUCW:
+	GLRO(dl_fpu_control) = av->a_un.a_val;
+	break;
 #ifdef NEED_DL_SYSINFO
       case AT_SYSINFO:
 	GL(dl_sysinfo) = av->a_un.a_val;
diff --git a/math/Makefile b/math/Makefile
index 3ed78fc..a9bd49b 100644
--- a/math/Makefile
+++ b/math/Makefile
@@ -87,9 +87,11 @@ long-c-yes = $(calls:=l)
 
 # Rules for the test suite.
 tests = test-matherr test-fenv atest-exp atest-sincos atest-exp2 basic-test \
-	test-misc test-fpucw tst-definitions test-tgmath test-tgmath-ret \
-	bug-nextafter bug-nexttoward bug-tgmath1 test-tgmath-int \
-	test-tgmath2 test-powl tst-CMPLX tst-CMPLX2 test-snan
+	test-misc test-fpucw test-fpucw-ieee tst-definitions test-tgmath \
+	test-tgmath-ret bug-nextafter bug-nexttoward bug-tgmath1 \
+	test-tgmath-int test-tgmath2 test-powl tst-CMPLX tst-CMPLX2 test-snan \
+	$(tests-static)
+tests-static = test-fpucw-static test-fpucw-ieee-static
 # We do the `long double' tests only if this data type is available and
 # distinct from `double'.
 test-longdouble-yes = test-ldouble test-ildoubl
@@ -217,7 +219,8 @@ $(objpfx)libieee.a: $(objpfx)ieee-math.o
 	$(LN_S) $(<F) $(@F)
 
 ifeq ($(build-shared),yes)
-$(addprefix $(objpfx),$(tests)): $(objpfx)libm.so$(libm.so-version)
+$(addprefix $(objpfx),$(filter-out $(tests-static),$(tests))): $(objpfx)libm.so$(libm.so-version)
+$(addprefix $(objpfx),$(tests-static)): $(objpfx)libm.a
 else
 $(addprefix $(objpfx),$(tests)): $(objpfx)libm.a
 endif
diff --git a/math/test-fpucw-ieee-static.c b/math/test-fpucw-ieee-static.c
new file mode 100644
index 0000000..3a35542
--- /dev/null
+++ b/math/test-fpucw-ieee-static.c
@@ -0,0 +1 @@
+#include "test-fpucw-ieee.c"
diff --git a/math/test-fpucw-ieee.c b/math/test-fpucw-ieee.c
new file mode 100644
index 0000000..ae5fc73
--- /dev/null
+++ b/math/test-fpucw-ieee.c
@@ -0,0 +1,24 @@
+/* FPU control word overridden initialization test.
+   Copyright (C) 2013 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/>.  */
+
+#define FPU_CONTROL _FPU_IEEE
+
+#include "test-fpucw.c"
+
+/* Preempt the library's definition of `__fpu_control'.  */
+fpu_control_t __fpu_control = _FPU_IEEE;
diff --git a/math/test-fpucw-static.c b/math/test-fpucw-static.c
new file mode 100644
index 0000000..bc1cfa8
--- /dev/null
+++ b/math/test-fpucw-static.c
@@ -0,0 +1 @@
+#include "test-fpucw.c"
diff --git a/math/test-fpucw.c b/math/test-fpucw.c
index 1961a67..ae6a2c9 100644
--- a/math/test-fpucw.c
+++ b/math/test-fpucw.c
@@ -19,6 +19,10 @@
 #include <fpu_control.h>
 #include <stdio.h>
 
+#ifndef FPU_CONTROL
+# define FPU_CONTROL _FPU_DEFAULT
+#endif
+
 int
 main (void)
 {
@@ -30,11 +34,11 @@ main (void)
 
   cw &= ~_FPU_RESERVED;
 
-  if (cw != (_FPU_DEFAULT & ~_FPU_RESERVED))
+  if (cw != (FPU_CONTROL & ~_FPU_RESERVED))
     printf ("control word is 0x%lx but should be 0x%lx.\n",
-	    (long int) cw, (long int) (_FPU_DEFAULT & ~_FPU_RESERVED));
+	    (long int) cw, (long int) (FPU_CONTROL & ~_FPU_RESERVED));
 
-  return cw != (_FPU_DEFAULT & ~_FPU_RESERVED);
+  return cw != (FPU_CONTROL & ~_FPU_RESERVED);
 
 #else
   return 0;