[gcc r12-8125] libstdc++: Prefer to use mmap instead of malloc in libbacktrace

[gcc r12-8125] libstdc++: Prefer to use mmap instead of malloc in libbacktrace

[Jonathan Wakely]

https://gcc.gnu.org/g:3c742621ed28540cf42d4cfbc2bf03433cd26738

commit r12-8125-g3c742621ed28540cf42d4cfbc2bf03433cd26738
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Apr 12 17:56:45 2022 +0100

    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.

Diff:
---
 libstdc++-v3/acinclude.m4 | 35 +++++++++++++++++++++++-----
 libstdc++-v3/config.h.in  |  3 +++
 libstdc++-v3/configure    | 59 ++++++++++++++++++++++++++++++++++++++++-------
 3 files changed, 83 insertions(+), 14 deletions(-)

diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index f53461c85a5..eac8aeda48b 100644
--- a/libstdc++-v3/acinclude.m4
+++ b/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
diff --git a/libstdc++-v3/config.h.in b/libstdc++-v3/config.h.in
index f6212de9268..f30a8c51c45 100644
--- a/libstdc++-v3/config.h.in
+++ b/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
 
diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
index ef80912d0b9..35dc3f49383 100755
--- a/libstdc++-v3/configure
+++ b/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