1# alloca.m4 serial 19
2dnl Copyright (C) 2002-2004, 2006-2007, 2009-2020 Free Software Foundation,
3dnl Inc.
4dnl This file is free software; the Free Software Foundation
5dnl gives unlimited permission to copy and/or distribute it,
6dnl with or without modifications, as long as this notice is preserved.
7
8AC_DEFUN([gl_FUNC_ALLOCA],
9[
10  AC_REQUIRE([AC_FUNC_ALLOCA])
11  if test $ac_cv_func_alloca_works = no; then
12    gl_PREREQ_ALLOCA
13  fi
14
15  # Define an additional variable used in the Makefile substitution.
16  if test $ac_cv_working_alloca_h = yes; then
17    AC_CACHE_CHECK([for alloca as a compiler built-in], [gl_cv_rpl_alloca], [
18      AC_EGREP_CPP([Need own alloca], [
19#if defined __GNUC__ || defined _AIX || defined _MSC_VER
20        Need own alloca
21#endif
22        ], [gl_cv_rpl_alloca=yes], [gl_cv_rpl_alloca=no])
23    ])
24    if test $gl_cv_rpl_alloca = yes; then
25      dnl OK, alloca can be implemented through a compiler built-in.
26      AC_DEFINE([HAVE_ALLOCA], [1],
27        [Define to 1 if you have 'alloca' after including <alloca.h>,
28         a header that may be supplied by this distribution.])
29      ALLOCA_H=alloca.h
30    else
31      dnl alloca exists as a library function, i.e. it is slow and probably
32      dnl a memory leak. Don't define HAVE_ALLOCA in this case.
33      ALLOCA_H=
34    fi
35  else
36    ALLOCA_H=alloca.h
37  fi
38  AC_SUBST([ALLOCA_H])
39  AM_CONDITIONAL([GL_GENERATE_ALLOCA_H], [test -n "$ALLOCA_H"])
40
41  if test $ac_cv_working_alloca_h = yes; then
42    HAVE_ALLOCA_H=1
43  else
44    HAVE_ALLOCA_H=0
45  fi
46  AC_SUBST([HAVE_ALLOCA_H])
47])
48
49# Prerequisites of lib/alloca.c.
50# STACK_DIRECTION is already handled by AC_FUNC_ALLOCA.
51AC_DEFUN([gl_PREREQ_ALLOCA], [:])
52
53m4_version_prereq([2.69c], [], [
54
55# This works around a bug in autoconf <= 2.68 and has simplifications
56# from 2.69c.  See:
57# https://lists.gnu.org/r/bug-gnulib/2011-06/msg00277.html
58# https://git.savannah.gnu.org/cgit/autoconf.git/commit/?id=6cd9f12520b0d6f76d3230d7565feba1ecf29497
59# https://git.savannah.gnu.org/cgit/autoconf.git/commit/?id=15edf7fd8094fd14a89d9891dd72a9624762597a
60
61# _AC_LIBOBJ_ALLOCA
62# -----------------
63# Set up the LIBOBJ replacement of 'alloca'.  Well, not exactly
64# AC_LIBOBJ since we actually set the output variable 'ALLOCA'.
65# Nevertheless, for Automake, AC_LIBSOURCES it.
66m4_define([_AC_LIBOBJ_ALLOCA],
67[# The SVR3 libPW and SVR4 libucb both contain incompatible functions
68# that cause trouble.  Some versions do not even contain alloca or
69# contain a buggy version.  If you still want to use their alloca,
70# use ar to extract alloca.o from them instead of compiling alloca.c.
71AC_LIBSOURCES(alloca.c)
72AC_SUBST([ALLOCA], [\${LIBOBJDIR}alloca.$ac_objext])dnl
73AC_DEFINE(C_ALLOCA, 1, [Define to 1 if using 'alloca.c'.])
74
75AC_CACHE_CHECK([stack direction for C alloca],
76               [ac_cv_c_stack_direction],
77[AC_RUN_IFELSE([AC_LANG_SOURCE(
78[AC_INCLUDES_DEFAULT
79int
80find_stack_direction (int *addr, int depth)
81{
82  int dir, dummy = 0;
83  if (! addr)
84    addr = &dummy;
85  *addr = addr < &dummy ? 1 : addr == &dummy ? 0 : -1;
86  dir = depth ? find_stack_direction (addr, depth - 1) : 0;
87  return dir + dummy;
88}
89
90int
91main (int argc, char **argv)
92{
93  return find_stack_direction (0, argc + !argv + 20) < 0;
94}])],
95               [ac_cv_c_stack_direction=1],
96               [ac_cv_c_stack_direction=-1],
97               [ac_cv_c_stack_direction=0])])
98AH_VERBATIM([STACK_DIRECTION],
99[/* If using the C implementation of alloca, define if you know the
100   direction of stack growth for your system; otherwise it will be
101   automatically deduced at runtime.
102        STACK_DIRECTION > 0 => grows toward higher addresses
103        STACK_DIRECTION < 0 => grows toward lower addresses
104        STACK_DIRECTION = 0 => direction of growth unknown */
105#undef STACK_DIRECTION])dnl
106AC_DEFINE_UNQUOTED(STACK_DIRECTION, $ac_cv_c_stack_direction)
107])
108])
109