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95e7cf295e
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 f8f900ecb9 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.
47 lines
1.3 KiB
C
47 lines
1.3 KiB
C
/* Copyright (C) 2000-2013 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Andreas Jaeger <aj@suse.de>, 2000.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <fpu_control.h>
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#include <stdio.h>
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#ifndef FPU_CONTROL
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# define FPU_CONTROL _FPU_DEFAULT
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#endif
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int
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main (void)
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{
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#ifdef _FPU_GETCW
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/* Some architectures don't have _FPU_GETCW (e.g. Linux/Alpha). */
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fpu_control_t cw;
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_FPU_GETCW (cw);
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cw &= ~_FPU_RESERVED;
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if (cw != (FPU_CONTROL & ~_FPU_RESERVED))
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printf ("control word is 0x%lx but should be 0x%lx.\n",
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(long int) cw, (long int) (FPU_CONTROL & ~_FPU_RESERVED));
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return cw != (FPU_CONTROL & ~_FPU_RESERVED);
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#else
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return 0;
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#endif
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}
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