[llvm-libgcc] Don't export __{,de}register_frame_info* and __register_frame_table

[MaskRay]

Summary

These symbols are used in the absence of PT_GNU_EH_FRAME, for ld
--no-eh-frame-hdr (gcc -static default).

libunwind defines these empty functions when
defined(_LIBUNWIND_BUILD_ZERO_COST_APIS) && defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND) && defined(_LIBUNWIND_SUPPORT_FRAME_APIS).
They should be perceived as Mac OS X workarounds.

For Linux, GCC crtbeginT.o (for -static) and clang_rt.crtbegin.o contain
weak references to __{,de}register_frame_info. Dynamically linked
executables will either not reference __{,de}register_frame_info (using
libgcc) or reference them as weak symbols (using compiler-rt).

Therefore, not defining these symbols is backward compatible.

[MaskRay]

Ｐｉｎｇ：）

[phosek]

LGTM

[cjdb]

Sorry, I didn't see the original email. Thanks for the patch: the reasoning makes sense to me.

llvm-libgcc/lib/gcc_s.ver

#elif defined(GLOBAL_64BIT)
 
   GCC_3.4   { __clzti2;      __ctzti2;  __parityti2; __popcountti2;           };
   GCC_3.4.4 { __absvti2;     __addvti3; __mulvti3;   __negvti2;    __subvti3; };
   GCC_4.2.0 { __floatuntidf; __floatuntisf;                                   };
   GCC_7.0.0 { __divmodti4;                                                    };
 #endif
 
 #if defined(GLOBAL_X86)
-  GCC_3.0 {
-    __deregister_frame_info_bases; __fixunsxfdi; __register_frame_info_bases;
-    __register_frame_info_table_bases;
-  };
-
+  GCC_3.0 { __fixunsxfdi; };
   GCC_4.0.0 { __divxc3; __mulxc3; __powixf2; };
   GCC_4.8.0 { __cpu_indicator_init;          };
 #endif
 
 #if !defined(ARM_GNUEABIHF)
   GCC_3.0 {
     _Unwind_Find_FDE; _Unwind_GetGR; _Unwind_GetIP; _Unwind_SetGR; _Unwind_SetIP;
   };

 
 #if defined(__aarch64__) || defined(__i386__)
   GLIBC_2.0 { __deregister_frame; __register_frame; };
 #endif
 
 #if defined(__i386__)
   GCC_3.0   { __fixunsxfsi; __fixxfdi; __floatdixf; };
   GCC_4.2.0 { __floatundixf; };
-
-  GLIBC_2.0 {
-    __register_frame_info; __register_frame_info_table; __register_frame_table;
-    __deregister_frame_info;
-  };
 #endif
 
 #if defined(__x86_64__)
   GCC_3.0 {
-    __register_frame_info; __register_frame_info_table; __register_frame_table;
-    __deregister_frame;    __deregister_frame_info;     __register_frame;
+    __deregister_frame;    __register_frame;
     __fixunsxfti;          __fixxfti;                   __floattixf;
   };
 
   GCC_4.2.0 { __floatuntixf; };
   GCC_4.3.0 { __divtc3; __multc3; };
 #endif