[PATCH v3 02/32] Mini-OS: explicitly mark symbols to be visible for apps

[Juergen Gross <jgross@xxxxxxxx>]

Add an EXPORT_SYMBOL() macro to explicitly mark a symbol to be visible
for an app or library linked with Mini-OS. This prepares hiding all
other symbols from external components, avoiding any problems with
duplicate symbol names.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V3:
- new patch
---
 .gitignore       |  1 +
 Makefile         |  3 ++-
 include/export.h | 10 ++++++++++
 include/lib.h    |  1 +
 4 files changed, 14 insertions(+), 1 deletion(-)
 create mode 100644 include/export.h

diff --git a/.gitignore b/.gitignore
index abef46b2..bacf787e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -16,3 +16,4 @@ mini-os.gz
 minios-config.mk
 mini-os-debug
 mini-os-debug.gz
+syms
diff --git a/Makefile b/Makefile
index 85c6db75..588496cb 100644
--- a/Makefile
+++ b/Makefile
@@ -166,10 +166,11 @@ $(OBJ_DIR)/arch/x86/minios-x86%.lds:  
arch/x86/minios-x86.lds.S
 
 $(OBJ_DIR)/$(TARGET)-kern.o: $(OBJS) arch_lib 
$(OBJ_DIR)/$(TARGET_ARCH_DIR)/minios-$(MINIOS_TARGET_ARCH).lds
        $(LD) -r $(LDFLAGS) $(HEAD_OBJ) $(OBJS) $(LDARCHLIB) -o $@
+       $(OBJCOPY) --dump-section .export_symbol=$(OBJ_DIR)/syms $@
 
 $(OBJ_DIR)/$(TARGET): $(OBJ_DIR)/$(TARGET)-kern.o $(APP_O)
        $(LD) -r $(LDFLAGS) $(OBJ_DIR)/$(TARGET)-kern.o $(APP_O) $(LDLIBS) -o 
$@.o
-       $(OBJCOPY) -w -G $(GLOBAL_PREFIX)* -G _start $@.o $@.o
+       $(OBJCOPY) -w -G $(GLOBAL_PREFIX)* -G _start 
--remove-section=.export_symbol $@.o $@.o
        $(LD) $(LDFLAGS) $(LDFLAGS_FINAL) $@.o $(EXTRA_OBJS) -o $@-debug
        strip -s $@-debug -o $@
        gzip -n -f -9 -c $@-debug >$@-debug.gz
diff --git a/include/export.h b/include/export.h
new file mode 100644
index 00000000..7140ac68
--- /dev/null
+++ b/include/export.h
@@ -0,0 +1,10 @@
+#ifndef _EXPORT_H_
+#define _EXPORT_H_
+
+/* Mark a symbol to be visible for apps and libs. */
+#define EXPORT_SYMBOL(sym)          \
+    asm(".section .export_symbol\n" \
+        ".ascii \""#sym"\\n\"\n"    \
+        ".previous\n")
+
+#endif /* _EXPORT_H_ */
diff --git a/include/lib.h b/include/lib.h
index dd68985a..abd4e9ab 100644
--- a/include/lib.h
+++ b/include/lib.h
@@ -53,6 +53,7 @@
 #include <stddef.h>
 #include <xen/xen.h>
 #include <xen/event_channel.h>
+#include <mini-os/export.h>
 #include "gntmap.h"
 
 #if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 6)
-- 
2.35.3