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1 dnl @synopsis AX_GCC_ALIGNS_STACK([ACTION-IF-YES], [ACTION-IF-NO])
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2 dnl @summary check whether gcc can align stack to 8-byte boundary
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3 dnl @category Misc
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4 dnl
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5 dnl Check to see if we are using a version of gcc that aligns the stack
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6 dnl (true in gcc-2.95+, which have the -mpreferred-stack-boundary flag).
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7 dnl Also, however, checks whether main() is correctly aligned by the
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8 dnl OS/libc/..., as well as for a bug in the stack alignment of gcc-2.95.x
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9 dnl (see http://gcc.gnu.org/ml/gcc-bugs/1999-11/msg00259.html).
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10 dnl
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11 dnl ACTION-IF-YES/ACTION-IF-NO are shell commands to execute if we are
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12 dnl using gcc and the stack is/isn't aligned, respectively.
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13 dnl
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14 dnl Requires macro: AX_CHECK_COMPILER_FLAGS, AX_GCC_VERSION
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15 dnl
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16 dnl @version 2005-05-30
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17 dnl @license GPLWithACException
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18 dnl @author Steven G. Johnson <stevenj@alum.mit.edu>
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19 AC_DEFUN([AX_GCC_ALIGNS_STACK],
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20 [
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21 AC_REQUIRE([AC_PROG_CC])
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22 ax_gcc_aligns_stack=no
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23 if test "$GCC" = "yes"; then
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24 AX_CHECK_COMPILER_FLAGS(-mpreferred-stack-boundary=4, [
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25 AC_MSG_CHECKING([whether the stack is at least 8-byte aligned by gcc])
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26 save_CFLAGS="$CFLAGS"
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27 CFLAGS="-O"
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28 AX_CHECK_COMPILER_FLAGS(-malign-double, CFLAGS="$CFLAGS -malign-double")
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29 AC_TRY_RUN([#include <stdlib.h>
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30 # include <stdio.h>
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31 struct yuck { int blechh; };
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32 int one(void) { return 1; }
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33 struct yuck ick(void) { struct yuck y; y.blechh = 3; return y; }
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34 # define CHK_ALIGN(x) if ((((long) &(x)) & 0x7)) { fprintf(stderr, "bad alignment of " #x "\n"); exit(1); }
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35 void blah(int foo) { double foobar; CHK_ALIGN(foobar); }
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36 int main2(void) {double ok1; struct yuck y; double ok2; CHK_ALIGN(ok1);
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37 CHK_ALIGN(ok2); y = ick(); blah(one()); return 0;}
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38 int main(void) { if ((((long) (__builtin_alloca(0))) & 0x7)) __builtin_alloca(4); return main2(); }
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39 ], [ax_gcc_aligns_stack=yes; ax_gcc_stack_align_bug=no],
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40 ax_gcc_stack_align_bug=yes, [AX_GCC_VERSION(3,0,0, ax_gcc_stack_align_bug=no, ax_gcc_stack_align_bug=yes)])
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41 CFLAGS="$save_CFLAGS"
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42 AC_MSG_RESULT($ax_gcc_aligns_stack)
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43 ])
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44 fi
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45 if test "$ax_gcc_aligns_stack" = yes; then
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46 m4_default([$1], :)
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47 else
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48 m4_default([$2], :)
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49 fi
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50 ])
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