[PATCH, C++] Warn on redefinition of builtin functions (PR c++/71973)

Joseph Myers joseph@codesourcery.com
Mon Oct 17 18:06:00 GMT 2016

On Sun, 16 Oct 2016, Bernd Edlinger wrote:

> Second, the declaration in the glibc header files simply look wrong,
> because the type of argv, and envp is "char *const *" while the
> builtin function wants "const char**", thus only the array of char*
> itself is const, not the actual char stings they point to.

char *const * is the POSIX type.  (It can't be const char ** or const char 
*const * because you can't convert char ** implicitly to those types in 
ISO C.)  You'd need to check the list archives for rationale for the 
built-in functions doing something different.

> Third, in C the  builtins are not diagnosed, because C does only look
> at the mode of the parameters see match_builtin_function_types in
> c/c-decl.c, which may itself be wrong, because that makes an ABI
> decision dependent on the mode of the parameter.

The matching needs to be loose because of functions using types such as 
FILE * where the compiler doesn't know the exact contents of the type when 
processing built-in function definitions.  (Historically there were also 
issues with pre-ISO headers, but that may be less relevant now.)

Joseph S. Myers

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