libstdc++: Prefer to use mmap instead of malloc in libbacktrace

As reported in PR libbacktrace/105240, libbacktrace leaks memory when
using malloc for allocations. I originally thought it would be simpler
to just use malloc unconditionally (because it's supported on all
targets) but the leaks make that problematic.

This adds libbacktrace's detection for mmap to the libstdc++
configury, so that we use mmap.c and mmapio.c when possible. This avoids
the leaks seen previously, at least on linux.

libstdc++-v3/ChangeLog:

	* acinclude.m4 (GLIBCXX_ENABLE_BACKTRACE): Check for mmap.
	* config.h.in: Regenerate.
	* configure: Regenerate.

libstdc++-v3/acinclude.m4

@@ -5003,18 +5003,41 @@ elf64) elfsize=64 ;;
 esac
 BACKTRACE_CPPFLAGS="$BACKTRACE_CPPFLAGS -DBACKTRACE_ELF_SIZE=$elfsize"
 
-  ALLOC_FILE=alloc.lo
-  AC_SUBST(ALLOC_FILE)
-  VIEW_FILE=read.lo
-  AC_SUBST(VIEW_FILE)
-
   AC_MSG_CHECKING([whether to build libbacktrace support])
   if test "$enable_libstdcxx_backtrace" == "auto"; then
     enable_libstdcxx_backtrace=no
   fi
   if test "$enable_libstdcxx_backtrace" == "yes"; then
     BACKTRACE_SUPPORTED=1
-    BACKTRACE_USES_MALLOC=1
+
+    AC_CHECK_HEADERS(sys/mman.h)
+    case "${host}" in
+      *-*-msdosdjgpp) # DJGPP has sys/man.h, but no mmap
+	have_mmap=no ;;
+      *-*-*)
+	have_mmap="$ac_cv_header_sys_mman_h" ;;
+    esac
+
+    if test "$have_mmap" = "no"; then
+      VIEW_FILE=read.lo
+      ALLOC_FILE=alloc.lo
+    else
+      VIEW_FILE=mmapio.lo
+      AC_PREPROC_IFELSE([AC_LANG_SOURCE([
+    #include <sys/mman.h>
+    #if !defined(MAP_ANONYMOUS) && !defined(MAP_ANON)
+      #error no MAP_ANONYMOUS
+    #endif
+    ])], [ALLOC_FILE=mmap.lo], [ALLOC_FILE=alloc.lo])
+    fi
+    AC_SUBST(VIEW_FILE)
+    AC_SUBST(ALLOC_FILE)
+
+    BACKTRACE_USES_MALLOC=0
+    if test "$ALLOC_FILE" = "alloc.lo"; then
+      BACKTRACE_USES_MALLOC=1
+    fi
+
     if test "$ac_has_gthreads" = "yes"; then
       BACKTRACE_SUPPORTS_THREADS=1
     else

libstdc++-v3/config.h.in

@@ -420,6 +420,9 @@
 /* Define to 1 if you have the <sys/machine.h> header file. */
 #undef HAVE_SYS_MACHINE_H
 
+/* Define to 1 if you have the <sys/mman.h> header file. */
+#undef HAVE_SYS_MMAN_H
+
 /* Define to 1 if you have the <sys/param.h> header file. */
 #undef HAVE_SYS_PARAM_H
 

libstdc++-v3/configure

@@ -681,8 +681,8 @@ BACKTRACE_SUPPORTS_THREADS
 BACKTRACE_USES_MALLOC
 BACKTRACE_SUPPORTED
 BACKTRACE_CPPFLAGS
-VIEW_FILE
 ALLOC_FILE
+VIEW_FILE
 FORMAT_FILE
 ENABLE_FILESYSTEM_TS_FALSE
 ENABLE_FILESYSTEM_TS_TRUE
@@ -16190,7 +16190,7 @@ ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
 
     ac_save_CXXFLAGS="$CXXFLAGS"
 
-        cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+                cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
     #if ! defined __GCC_HAVE_SYNC_COMPARE_AND_SWAP_2
@@ -77463,11 +77463,6 @@ elf64) elfsize=64 ;;
 esac
 BACKTRACE_CPPFLAGS="$BACKTRACE_CPPFLAGS -DBACKTRACE_ELF_SIZE=$elfsize"
 
-  ALLOC_FILE=alloc.lo
-
-  VIEW_FILE=read.lo
-
-
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether to build libbacktrace support" >&5
 $as_echo_n "checking whether to build libbacktrace support... " >&6; }
   if test "$enable_libstdcxx_backtrace" == "auto"; then
@@ -77475,7 +77470,55 @@ $as_echo_n "checking whether to build libbacktrace support... " >&6; }
   fi
   if test "$enable_libstdcxx_backtrace" == "yes"; then
     BACKTRACE_SUPPORTED=1
-    BACKTRACE_USES_MALLOC=1
+
+    for ac_header in sys/mman.h
+do :
+  ac_fn_c_check_header_mongrel "$LINENO" "sys/mman.h" "ac_cv_header_sys_mman_h" "$ac_includes_default"
+if test "x$ac_cv_header_sys_mman_h" = xyes; then :
+  cat >>confdefs.h <<_ACEOF
+#define HAVE_SYS_MMAN_H 1
+_ACEOF
+
+fi
+
+done
+
+    case "${host}" in
+      *-*-msdosdjgpp) # DJGPP has sys/man.h, but no mmap
+	have_mmap=no ;;
+      *-*-*)
+	have_mmap="$ac_cv_header_sys_mman_h" ;;
+    esac
+
+    if test "$have_mmap" = "no"; then
+      VIEW_FILE=read.lo
+      ALLOC_FILE=alloc.lo
+    else
+      VIEW_FILE=mmapio.lo
+      cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+    #include <sys/mman.h>
+    #if !defined(MAP_ANONYMOUS) && !defined(MAP_ANON)
+      #error no MAP_ANONYMOUS
+    #endif
+
+_ACEOF
+if ac_fn_c_try_cpp "$LINENO"; then :
+  ALLOC_FILE=mmap.lo
+else
+  ALLOC_FILE=alloc.lo
+fi
+rm -f conftest.err conftest.i conftest.$ac_ext
+    fi
+
+
+
+    BACKTRACE_USES_MALLOC=0
+    if test "$ALLOC_FILE" = "alloc.lo"; then
+      BACKTRACE_USES_MALLOC=1
+    fi
+
     if test "$ac_has_gthreads" = "yes"; then
       BACKTRACE_SUPPORTS_THREADS=1
     else