Symbol export whitelist

Before modules were dynamically loaded the boundary between GPL and
non-GPL code was implicit because of the separate link domains for
each module. With dynamic modules we need an explicit whitelist of
core symbols that non-GPL code can link against at runtime without
needing to be re-licensed under the GPL.

Mark such symbols with __export, so that it is explicitly clear which
symbols in the core can be linked against by non-GPL code.

Reduce the visibility of symbols in both the core and ldlinux.c32 with
-fvisibility=hidden. __export changes the visibility to 'default'.

Signed-off-by: Matt Fleming <matt.fleming@intel.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/com32/elflink/ldlinux/readconfig.c b/com32/elflink/ldlinux/readconfig.c
index 7411fcaf..6a419c6d 100644
--- a/com32/elflink/ldlinux/readconfig.c
+++ b/com32/elflink/ldlinux/readconfig.c
@@ -82,10 +82,11 @@ short vkernel = 0;		//have we seen any "label" statements?
 short displaycon = 1;		//conio.inc
 extern short NoHalt;		//idle.c
 
-const char *default_cmd = NULL;	//"default" command line
 const char *onerror = NULL;	//"onerror" command line
 const char *ontimeout = NULL;	//"ontimeout" command line
 
+__export const char *default_cmd = NULL;	//"default" command line
+
 /* Empty refstring */
 const char *empty_string;
 
@@ -599,7 +600,7 @@ uint32_t parse_argb(char **p)
 //static const char *append = NULL;
 extern const char *append;
 //static unsigned int ipappend = 0;
-unsigned int ipappend = 0;
+__export unsigned int ipappend = 0;
 extern uint16_t PXERetry;
 static struct labeldata ld;