Implemented --enable-hidden-symbols configure option to enable

-fvisibility=hidden on gcc >= 4.0.  This reduces the size of the libcurl
binary and speeds up dynamic linking by hiding all the internal symbols from
the symbol table.

3 files changed, 56 insertions, 5 deletions

diff --git a/configure.ac b/configure.ac
index 41ebf6000..bb44612cf 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1954,6 +1954,29 @@ AC_HELP_STRING([--disable-cookies],[Disable cookies support]),
        AC_MSG_RESULT(yes)
 )
 
+dnl ************************************************************
+dnl Enable hiding of internal symbols in library to reduce its size and
+dnl speed dynamic linking of applications.  This currently is only supported
+dnl on gcc >= 4.0
+dnl
+AC_MSG_CHECKING([whether to enable hidden symbols in the library])
+AC_ARG_ENABLE(hidden-symbols,
+AC_HELP_STRING([--enable-hidden-symbols],[Hide internal symbols in library (gcc>=4)])
+AC_HELP_STRING([--disable-hidden-symbols],[Leave all symbols with default visibility in library]),
+[ case "$enableval" in
+  no)
+       AC_MSG_RESULT(no)
+       ;;
+  *)   AC_MSG_RESULT(yes)
+       AC_DEFINE(CURL_HIDDEN_SYMBOLS, 1, [to enable hidden symbols])
+       AC_SUBST(CURL_HIDDEN_SYMBOLS)
+       CFLAGS="$CFLAGS -fvisibility=hidden"
+       ;;
+  esac ],
+       AC_MSG_RESULT(no)
+)
+
+dnl ************************************************************
 if test "x$ws2" = "xyes"; then
 
   dnl If ws2_32 is wanted, make sure it is the _last_ lib in LIBS (makes
diff --git a/docs/INSTALL b/docs/INSTALL
index b44168051..c892283b2 100644
--- a/docs/INSTALL
+++ b/docs/INSTALL
@@ -506,13 +506,17 @@ CROSS COMPILE
 
        ./configure --host=ARCH-OS
 
+REDUCING SIZE
+=============
+
    There are a number of configure options that can be used to reduce the
    size of libcurl for embedded applications where binary size is an
-   important factor.  First, be sure to set the CFLAGS environment variable
-   when configuring with any compiler optimization flags to reduce the
-   size of the binary.  For gcc, this would mean at minimum:
+   important factor.  First, be sure to set the CFLAGS variable when
+   configuring with any relevant compiler optimization flags to reduce the
+   size of the binary.  For gcc, this would mean at minimum the -Os option
+   and probably the -march=X option as well, e.g.:
 
-      env CFLAGS='-Os' ./configure ...
+      ./configure CFLAGS='-Os' ...
 
    Be sure to specify as many --disable- and --without- flags on the configure
    command-line as you can to disable all the libcurl features that you
@@ -526,10 +530,24 @@ CROSS COMPILE
      --disable-crypto-auth (disables HTTP cryptographic authentication)
      --disable-ipv6 (disables support for IPv6)
      --disable-verbose (eliminates debugging strings and error code strings)
+     --enable-hidden-symbols (eliminates unneeded symbols in library)
      --without-libidn (disables support for the libidn DNS library)
      --without-ssl (disables support for SSL/TLS)
      --without-zlib (disables support for on-the-fly decompression)
 
+   The GNU linker has a number of options to reduce the size of the libcurl
+   dynamic libraries on some platforms even further. Specify them by giving
+   the options -Wl,-Bsymbolic and -Wl,-s on the gcc command-line.  
+   Be sure also to strip debugging symbols from your binaries after
+   compiling using 'strip' (or the appropriate variant if cross-compiling).
+   If space is really tight, you may be able to remove some unneeded
+   sections of the library using the -R option to objcopy (e.g. the
+   .comment section).
+
+   Using these techniques it is possible to create an HTTP-only shared
+   libcurl library for i386 Linux platforms that is less than 90 KB in
+   size (as of version 7.15.4).
+
    You may find that statically linking libcurl to your application will
    result in a lower total size.
 
diff --git a/include/curl/curl.h b/include/curl/curl.h
index 94c4551e0..bd9236ed3 100644
--- a/include/curl/curl.h
+++ b/include/curl/curl.h
@@ -58,7 +58,17 @@ extern "C" {
 #define CURL_EXTERN  __declspec(dllimport)
 #endif
 #else
-#define CURL_EXTERN
+
+#ifdef CURL_HIDDEN_SYMBOLS
+/*
+ * On gcc >= 4 if -fvisibility=hidden is given then this is used to cause
+ * external definitions to be put into the shared library.  It makes no
+ * difference to applications whether this is set or not, only the library.
+ */
+#define CURL_EXTERN __attribute__ ((visibility ("default")))
+#else
+#define CURL_EXTERN 
+#endif
 #endif
 
 /*