[perl #126240] use -DPERL_USE_SAFE_PUTENV where possible on OS X

On threaded builds on OS X, libSystem registers atfork handlers that
call setenv(), which internally modifies members of environ[], setting
them to malloc()ed blocks.

In some cases Perl_my_setenv() reallocates environ[] using
safesysmalloc(), which under debugging builds adds a tracking header,
and if perl_destruct() sees that environ[] has been reallocated, frees
it with safesysfree().

When these combine, perl attempts to free the malloc()ed block with
safesysfree(), which attempts to access the tracking header, causing
an invalid access in tools like valgrind, or a "free from wrong pool"
error, since the header contains unrelated data.

Avoid this mess by letting libc manage environ[] if unsetenv() is
available.

1 files changed, 10 insertions, 0 deletions

diff --git a/hints/darwin.sh b/hints/darwin.sh
index ee2076013b..2af6ae7331 100644
--- a/hints/darwin.sh
+++ b/hints/darwin.sh
@@ -490,3 +490,13 @@ esac
 # makefile in the same place.  Since Darwin uses GNU make, this dodges
 # the problem.
 firstmakefile=GNUmakefile;
+
+# Parts of the system call setenv(), in particular in an atfork handler.
+# This causes problems when the child tries to clean up environ[], so
+# let libc manage environ[].
+cat >> config.over <<'EOOVER'
+if test "$d_unsetenv" = "$define" -a \
+    `expr "$ccflags" : '.*-DPERL_USE_SAFE_PUTENV'` -eq 0; then
+        ccflags="$ccflags -DPERL_USE_SAFE_PUTENV"
+fi
+EOOVER