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From: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>
References: <cover.1586650013.git.v.shpilevoy@tarantool.org>
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Date: Thu, 16 Apr 2020 01:15:45 +0200
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Subject: Re: [Tarantool-patches] [PATCH 00/43] Unhide symbols
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To: tarantool-patches@dev.tarantool.org

With help of Timur there was a discovered a little less
intrusive solution: a little hack with the compiler.

Consider this diff:

====================
diff --git a/src/exports.c b/src/exports.c
index de1892026..47fe1b9bd 100644
--- a/src/exports.c
+++ b/src/exports.c
@@ -30,6 +30,11 @@
  */
 #define EXPORT(func) extern void ** func(void)
 
+#include <time.h>
+
+extern void *bit_unused_function;
+extern void *bit_symbol;
+
 /**
  * The file is a hack to force the linker keep the needed symbols
  * in the result tarantool executable file.
@@ -121,6 +126,11 @@ export_syms(void)
 	const int func_count = sizeof(syms) / sizeof(syms[0]);
 	for (int i = 0; i < func_count; ++i)
 		((void **(*)(void))syms[i])();
+	if (time(NULL) == 0)
+	{
+		((void **(*)(void))bit_unused_function)();
+		((void **(*)(void))bit_symbol)();
+	}
 }
 
 #undef EXPORT
diff --git a/src/lib/bit/bit.c b/src/lib/bit/bit.c
index 72cc94dc3..94fe75408 100644
--- a/src/lib/bit/bit.c
+++ b/src/lib/bit/bit.c
@@ -31,6 +31,15 @@
 
 #include "bit/bit.h"
 
+void
+bit_unused_function(void)
+{
+	printf("Unused\n");
+	return;
+}
+
+int bit_symbol = 0;
+
 extern inline uint8_t
 load_u8(const void *p);
 
====================

As you can see, I managed to reference the needed symbols from a
static library without doing any includes. It means, we can
resurrect ffi_syms.c like it was before, but in a much simpler
manner, with 0 dependencies. Only extern void * of needed
variables and functions.