hide private functions with __attribute__((visibility("hidden")))

This allows us to enforce API boundaries and potentially enables
compiler optimisations.

We've been always hiding non-public symbols on Windows. This commit
brings that to the other platforms.

1 files changed, 30 insertions, 0 deletions

diff --git a/Configure b/Configure
index ee63ae6047..723ed94676 100755
--- a/Configure
+++ b/Configure
@@ -391,6 +391,7 @@ d_attribute_nonnull=''
 d_attribute_noreturn=''
 d_attribute_pure=''
 d_attribute_unused=''
+d_attribute_visibility=''
 d_attribute_warn_unused_result=''
 d_printf_format_null=''
 d_backtrace=''
@@ -11337,6 +11338,34 @@ set d_attribute_always_inline
 eval $setvar
 $rm -f attrib*
 
+: Look for GCC-style attribute visibility
+case "$d_attribute_visibility" in
+'')
+echo " "
+echo "Checking whether your compiler can handle __attribute__((visibility)) ..." >&4
+$cat >attrib.c <<'EOCP'
+#include <stdio.h>
+__attribute__((visibility("hidden"))) int I_will_be_hidden(void);
+EOCP
+if $cc $ccflags -c attrib.c >attrib.out 2>&1 ; then
+        if $compiler_warning attrib.out >/dev/null 2>&1; then
+                echo "Your C compiler doesn't support __attribute__((visibility))."
+                val="$undef"
+        else
+                echo "Your C compiler supports __attribute__((visibility))."
+                val="$define"
+        fi
+else
+        echo "Your C compiler doesn't seem to understand __attribute__ at all."
+        val="$undef"
+fi
+;;
+*) val="$d_attribute_visibility" ;;
+esac
+set d_attribute_visibility
+eval $setvar
+$rm -f attrib*
+
 : see if getpgrp exists
 set getpgrp d_getpgrp
 eval $inlibc
@@ -24598,6 +24627,7 @@ d_attribute_nonnull='$d_attribute_nonnull'
 d_attribute_noreturn='$d_attribute_noreturn'
 d_attribute_pure='$d_attribute_pure'
 d_attribute_unused='$d_attribute_unused'
+d_attribute_visibility='$d_attribute_visibility'
 d_attribute_warn_unused_result='$d_attribute_warn_unused_result'
 d_backtrace='$d_backtrace'
 d_bsd='$d_bsd'