Export public functions implemented in assembly on Windows.

[cdavis5x]

Summary

By default, symbols aren't visible outside of the module that defines
them. To make them visible, they must be exported. The easiest way to do
that is to embed an -export:symname directive into the object file.

[rnk]

src/assembly.h

76–78 ↗

(On Diff #163414)

Maybe .pushsection / .popsection is better than assuming you were in .text.

[cdavis5x]

src/assembly.h

76–78 ↗

(On Diff #163414)

I initially wanted to do that, but those directives aren't supported by COFF. Neither, by the way, is .previous. Perhaps this needs to be fixed in LLVM.

[rnk]

lgtm

src/assembly.h

76–78 ↗

(On Diff #163414)

Huh, I guess neither does gas. .text is fine then. I'll file a bug to implement those directives for COFF. They're pretty handy, especially for an object file format that uses comdat sections so frequently.

libunwind/trunk/src/assembly.h

 
 #define GLUE2(a, b) a ## b
 #define GLUE(a, b) GLUE2(a, b)
 #define SYMBOL_NAME(name) GLUE(__USER_LABEL_PREFIX__, name)
 
 #if defined(__APPLE__)
 
 #define SYMBOL_IS_FUNC(name)
+#define EXPORT_SYMBOL(name)
 #define HIDDEN_SYMBOL(name) .private_extern name
 #define NO_EXEC_STACK_DIRECTIVE
 
 #elif defined(__ELF__)
 
 #if defined(__arm__)
 #define SYMBOL_IS_FUNC(name) .type name,%function
 #else
 #define SYMBOL_IS_FUNC(name) .type name,@function
 #endif
+#define EXPORT_SYMBOL(name)
 #define HIDDEN_SYMBOL(name) .hidden name
 
 #if defined(__GNU__) || defined(__FreeBSD__) || defined(__Fuchsia__) || \
     defined(__linux__)
 #define NO_EXEC_STACK_DIRECTIVE .section .note.GNU-stack,"",%progbits
 #else
 #define NO_EXEC_STACK_DIRECTIVE
 #endif
 
 #elif defined(_WIN32)
 
 #define SYMBOL_IS_FUNC(name)                                                   \
   .def name SEPARATOR                                                          \
     .scl 2 SEPARATOR                                                           \
     .type 32 SEPARATOR                                                         \
   .endef
+#define EXPORT_SYMBOL2(name)                              \
+  .section .drectve,"yn" SEPARATOR                        \
+  .ascii "-export:", #name, "\0" SEPARATOR                \
+  .text
+#define EXPORT_SYMBOL(name) EXPORT_SYMBOL2(name)
 #define HIDDEN_SYMBOL(name)
 
 #define NO_EXEC_STACK_DIRECTIVE
 
 #else
 
 #error Unsupported target
 
 #endif
 
 #define DEFINE_LIBUNWIND_FUNCTION(name)                   \
   .globl SYMBOL_NAME(name) SEPARATOR                      \
+  EXPORT_SYMBOL(name) SEPARATOR                           \
   SYMBOL_IS_FUNC(SYMBOL_NAME(name)) SEPARATOR             \
   SYMBOL_NAME(name):
 
 #define DEFINE_LIBUNWIND_PRIVATE_FUNCTION(name)           \
   .globl SYMBOL_NAME(name) SEPARATOR                      \
   HIDDEN_SYMBOL(SYMBOL_NAME(name)) SEPARATOR              \
   SYMBOL_IS_FUNC(SYMBOL_NAME(name)) SEPARATOR             \
   SYMBOL_NAME(name):