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compiler: Explain the slim hidden macros.

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The slim_hidden_* macro definitions are rather cryptic at first
sight and I keep needing to rederive how they work just find out
what they're supposed to do.  This patch adds a comment explaining
how they're used and work.
This commit is contained in:
M Joonas Pihlaja 2010-02-25 13:58:53 +02:00
parent dcf897967d
commit ef807119ff
1 changed files with 30 additions and 0 deletions
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30
src/cairo-compiler-private.h
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@ -53,6 +53,36 @@
#define CAIRO_STACK_ARRAY_LENGTH(T) (CAIRO_STACK_BUFFER_SIZE / sizeof(T))
/*
* The goal of this block is to define the following macros for
* providing faster linkage to functions in the public API for calls
* from within cairo.
*
* slim_hidden_proto(f)
* slim_hidden_proto_no_warn(f)
*
* Declares `f' as a library internal function and hides the
* function from the global symbol table. This macro must be
* expanded after `f' has been declared with a prototype but before
* any calls to the function are seen by the compiler. The no_warn
* variant inhibits warnings about the return value being unused at
* call sites. The macro works by renaming `f' to an internal name
* in the symbol table and hiding that. As far as cairo internal
* calls are concerned they're calling a library internal function
* and thus don't need to bounce via the PLT.
*
* slim_hidden_def(f)
*
* Exports `f' back to the global symbol table. This macro must be
* expanded right after the function definition and only for symbols
* hidden previously with slim_hidden_proto(). The macro works by
* adding a global entry to the symbol table which points at the
* internal name of `f' created by slim_hidden_proto().
*
* Functions in the public API which aren't called by the library
* don't need to be hidden and re-exported using the slim hidden
* macros.
*/
#if __GNUC__ >= 3 && defined(__ELF__) && !defined(__sun)
# define slim_hidden_proto(name) slim_hidden_proto1(name, slim_hidden_int_name(name)) cairo_private
# define slim_hidden_proto_no_warn(name) slim_hidden_proto1(name, slim_hidden_int_name(name)) cairo_private_no_warn