[build] Use weak definitions instead of weak declarations

This removes the need for inline safety wrappers, marginally reducing
the size penalty of weak functions, and works around an apparent
binutils bug that causes undefined weak symbols to not actually be
NULL when compiling with -fPIE (as EFI builds do).

A bug in versions of binutils prior to 2.16 (released in 2005) will
cause same-file weak definitions to not work with those
toolchains. Update the README to reflect our new dependency on
binutils >= 2.16.

Signed-off-by: Joshua Oreman <oremanj@rwcr.net>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

README

-iPXE README File
-
-Quick start guide:
-
-   cd src
-   make
-
-For any more detailed instructions, see http://ipxe.org

src/arch/i386/include/pxe_call.h

 extern int pxe_deactivate ( void );
 extern int pxe_start_nbp ( void );
 extern __asmcall void pxe_api_call ( struct i386_all_regs *ix86 );
-extern int _pxe_api_call_weak ( struct i386_all_regs *ix86 )
-	__attribute__ (( weak ));
-
-/**
- * Dispatch PXE API call weakly
- *
- * @v ix86		Registers for PXE call
- * @ret present		Zero if the PXE stack is present, nonzero if not
- *
- * A successful return only indicates that the PXE stack was available
- * for dispatching the call; it says nothing about the success of
- * whatever the call asked for.
- */
-static inline int pxe_api_call_weak ( struct i386_all_regs *ix86 )
-{
-	if ( _pxe_api_call_weak != NULL )
-		return _pxe_api_call_weak ( ix86 );
-	return -1;
-}
+extern int pxe_api_call_weak ( struct i386_all_regs *ix86 );
 
 #endif /* _PXE_CALL_H */

src/arch/i386/interface/pxe/pxe_call.c

  * @v ix86		Registers for PXE call
  * @ret present		Zero (PXE stack present)
  */
-int _pxe_api_call_weak ( struct i386_all_regs *ix86 )
+int pxe_api_call_weak ( struct i386_all_regs *ix86 )
 {
 	pxe_api_call ( ix86 );
 	return 0;

src/arch/i386/interface/pxeparent/pxeparent_dhcp.c

 /**
  * Present cached DHCP packet if it exists
  */
-void __weak_impl ( get_cached_dhcpack ) ( void ) {
+void get_cached_dhcpack ( void ) {
 	struct undi_device *undi;
 	struct s_PXENV_GET_CACHED_INFO get_cached_info;
 	int rc;

src/arch/i386/interface/syslinux/comboot_call.c

 }
 
 
+/**
+ * Dispatch PXE API call weakly
+ *
+ * @v ix86		Registers for PXE call
+ * @ret present		Zero if the PXE stack is present, nonzero if not
+ *
+ * A successful return only indicates that the PXE stack was available
+ * for dispatching the call; it says nothing about the success of
+ * whatever the call asked for.
+ */
+__weak int pxe_api_call_weak ( struct i386_all_regs *ix86 __unused ) {
+	return -1;
+}
+
 /**
  * SYSLINUX API
  */

src/include/compiler.h

 /** Select file identifier for errno.h (if used) */
 #define ERRFILE PREFIX_OBJECT ( ERRFILE_ )
 
-/**
- * @defgroup weakmacros Macros to manage weak symbol definitions
- *
- * Weak symbols allow one to reference a function in another file
- * without necessarily requiring that file to be linked in. In their
- * native form, the function will be @c NULL if its file is not linked
- * in; these macros provide an inline wrapper that returns an
- * appropriate error indication or default value.
- *
- * @{
- */
 #ifndef ASSEMBLY
 
-/** Mangle @a name into its weakly-referenced implementation */
-#define __weak_impl( name )   _w_ ## name
-
-/**
- * Declare a weak function with inline safety wrapper
- *
- * @v ret	Return type of weak function
- * @v name	Name of function to expose
- * @v proto	Parenthesized list of arguments with types
- * @v args	Parenthesized list of argument names
- * @v dfl	Value to return if weak function is not available
- */
-#define __weak_decl( ret, name, proto, args, dfl )		\
-        ret __weak_impl( name ) proto __attribute__ (( weak ));	\
-        static inline ret name proto {				\
-                if ( __weak_impl( name ) )			\
-                        return __weak_impl( name ) args;	\
-                return dfl;					\
-        }
+/** Declare a function as weak (use *before* the definition) */
+#define __weak		__attribute__ (( weak ))
 
 #endif
-/** @} */
 
 /** @defgroup dbg Debugging infrastructure
  * @{

src/include/ipxe/dhcp.h

  * should look for such a packet and call store_cached_dhcpack() with
  * it if it exists.
  */
-__weak_decl ( void, get_cached_dhcpack, ( void ), (), );
+extern void get_cached_dhcpack ( void );
 
 extern void store_cached_dhcpack ( userptr_t data, size_t len );
 

src/include/ipxe/sec80211.h

 /** @file
  *
  * Definitions for general secured-network routines.
- *
- * Any function in this file which may be referenced by code which is
- * not exclusive to encryption-enabled builds (e.g. sec80211_detect(),
- * which is called by net80211_probe_step() to fill the net80211_wlan
- * structure's security fields) must be declared as a weak symbol,
- * using an inline interface similar to that used for
- * sec80211_detect() below. This prevents secure network support from
- * bloating general builds by any more than a few tiny hooks to call
- * crypto functions when crypto structures are non-NULL.
  */
 
-int _sec80211_detect ( struct io_buffer *iob,
-		       enum net80211_security_proto *secprot,
-		       enum net80211_crypto_alg *crypt )
-	__attribute__ (( weak ));
-
-
-/**
- * Inline safety wrapper for _sec80211_detect()
- *
- * @v iob	I/O buffer containing beacon frame
- * @ret secprot	Security handshaking protocol used by network
- * @ret crypt	Cryptosystem used by network
- * @ret rc	Return status code
- *
- * This function transparently calls _sec80211_detect() if the file
- * containing it was compiled in, or returns an error indication of
- * @c -ENOTSUP if not.
- */
-static inline int sec80211_detect ( struct io_buffer *iob,
-				    enum net80211_security_proto *secprot,
-				    enum net80211_crypto_alg *crypt ) {
-	if ( _sec80211_detect )
-		return _sec80211_detect ( iob, secprot, crypt );
-	return -ENOTSUP;
-}
+int sec80211_detect ( struct io_buffer *iob,
+		      enum net80211_security_proto *secprot,
+		      enum net80211_crypto_alg *crypt );
 
 int sec80211_detect_ie ( int is_rsn, u8 *start, u8 *end,
 			 enum net80211_security_proto *secprot,

src/include/usr/autoboot.h

 					   const char *filename );
 extern int boot_root_path ( const char *root_path );
 
-extern int pxe_menu_boot ( struct net_device *netdev )
-	__attribute__ (( weak ));
+extern int pxe_menu_boot ( struct net_device *netdev );
 
 #endif /* _USR_AUTOBOOT_H */

src/net/80211/net80211.c

 	int times_tried;
 };
 
+/**
+ * Detect secure 802.11 network when security support is not available
+ *
+ * @return -ENOTSUP, always.
+ */
+__weak int sec80211_detect ( struct io_buffer *iob __unused,
+			     enum net80211_security_proto *secprot __unused,
+			     enum net80211_crypto_alg *crypt __unused ) {
+	return -ENOTSUP;
+}
+
 /**
  * @defgroup net80211_netdev Network device interface functions
  * @{

src/net/udp/dhcp.c

 	.sa_family = AF_INET,
 };
 
+/**
+ * Get cached DHCPACK where none exists
+ */
+__weak void get_cached_dhcpack ( void ) {}
+
 /**
  * Start DHCP state machine on a network device
  *

src/usr/autoboot.c

 /** Shutdown flags for exit */
 int shutdown_exit_flags = 0;
 
+/**
+ * Perform PXE menu boot when PXE stack is not available
+ */
+__weak int pxe_menu_boot ( struct net_device *netdev __unused ) {
+	return -ENOTSUP;
+}
+
 /**
  * Identify the boot network device
  *
 			       buf, sizeof ( buf ) );
 	pxe_discovery_control =
 		fetch_uintz_setting ( NULL, &pxe_discovery_control_setting );
-	if ( ( strcmp ( buf, "PXEClient" ) == 0 ) && pxe_menu_boot != NULL &&
+	if ( ( strcmp ( buf, "PXEClient" ) == 0 ) &&
 	     setting_exists ( NULL, &pxe_boot_menu_setting ) &&
 	     ( ! ( ( pxe_discovery_control & PXEBS_SKIP ) &&
 		   setting_exists ( NULL, &filename_setting ) ) ) ) {