Symbol versioning works

Author: cirosantilli

shared-library/symbol-version/Makefile

@@ -2,16 +2,26 @@ CC := gcc -pedantic-errors -std=c89 -Wall -Wextra
 
 .PHONY: all clean run
 
-main.out: main.o libcirosantilli_a.so
-	$(CC) -L'.' main.o -o '$@' -lcirosantilli_a
+all: main.out main1.out main2.out
 
-run: main.out
+run: all
 	LD_LIBRARY_PATH=. ./main.out
+	LD_LIBRARY_PATH=. ./main1.out
+	LD_LIBRARY_PATH=. ./main2.out
+
+main.out: main.c libcirosantilli_a.so
+	$(CC) -L'.' main.c -o '$@' -lcirosantilli_a
+
+main1.out: main.c libcirosantilli_a.so
+	$(CC) -DV1 -L'.' main.c -o '$@' -lcirosantilli_a
+
+main2.out: main.c libcirosantilli_a.so
+	$(CC) -DV2 -L'.' main.c -o '$@' -lcirosantilli_a
 
 libcirosantilli_a.so: a.o
 	$(CC) -Wl,--version-script,a.map -L'.' -shared a.o -o '$@'
 
-%.o: %.c
+libcirosantilli_a.o: a.c
 	$(CC) -fPIC -c '$<' -o '$@'
 
 clean:

shared-library/symbol-version/README.md

@@ -2,4 +2,6 @@
 
 Trying to replicate glibc's `symbol@@VERSION` madness.
 
-TODO: not working, and I have no idea what I'm doing.
+This allows you to have a single library `v2`, that also contains symbols from `v1`.
+
+<https://www.technovelty.org/c/symbol-versions-and-dependencies.html> contains a nice example.

shared-library/symbol-version/a.c

@@ -4,10 +4,11 @@
 
 __asm__(".symver a1,a@LIBA_1");
 void a1(void) {
-    puts("a");
+    puts("a1");
 }
 
-__asm__(".symver a2,a@LIBA_2");
+/* @@ means "default version". */
+__asm__(".symver a2,a@@LIBA_2");
 void a2(void) {
-    puts("a");
+    puts("a2");
 }

shared-library/symbol-version/main.c

@@ -3,7 +3,13 @@
 
 #include "a.h"
 
-__asm__(".symver a1,a@LIBA_1");
+/* TODO: any clearer way of doing this maybe
+ * with some compilation option only? */
+#if defined(V1)
+__asm__(".symver a,a@LIBA_1");
+#elif defined(V2)
+__asm__(".symver a,a@LIBA_2");
+#endif
 
 int main(void) {
     a();