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Reputation: 43

libc_hidden_proto macro in gnu library C

in gnu library C source code, man could see some of functions prototype are followed with libc_hidden_proto macro, what is used for.

Upvotes: 2

Views: 749

Answers (1)

Employed Russian
Employed Russian

Reputation: 213756

what is used for.

It's documented in inlcude/libc-symbols.h:

/* The following macros are used for PLT bypassing within libc.so
   (and if needed other libraries similarly).
   First of all, you need to have the function prototyped somewhere,
   say in foo/foo.h:

   int foo (int __bar);

   If calls to foo within libc.so should always go to foo defined in libc.so,
   then in include/foo.h you add:

   libc_hidden_proto (foo)

   line and after the foo function definition:

   int foo (int __bar)
   {
     return __bar;
   }
   libc_hidden_def (foo)

   or

   int foo (int __bar)
   {
     return __bar;
   }
   libc_hidden_weak (foo)

In other words, this allows GLIBC to call e.g. __mmap which is defined inside libc.so.6 even if you LD_PRELOADed some other library which defines its own __mmap.

Upvotes: 3

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