Re: #pragma weak conformance

[David Edelsohn <dje at watson dot ibm dot com>]

>>>>> Geoff Keating writes:

Geoff> I believe that GCC is trying to conform to the union of all the
Geoff> implementations out there.  '#pragma weak' is only for compatibility
Geoff> with other implementations, so it should try to be compatible with as
Geoff> many other implementations as possible :-).

	The problem is:

#pragma weak foo=bar

as opposed to

extern bar __attribute__ ((weak, alias ("foo")))

	The former calls ASM_OUTPUT_WEAK_ALIAS from weak_finish() while
the latter calls ASM_OUTPUT_DEF_FROM_DECLS from assemble_weak().  Not
calling ASM_OUTPUT_DEF_FROM_DECLS means that some additional machinery
necessary for a weak function may not be invokved.  The pragma case does
not have any associated DECL.

	The Solaris semantics require that an alias of an identifier match
a declaration.  Is there any way to find the GCC declaration associated
with an identifier?

	What I am proposing is something along the lines of the following
patch.  The main piece missing is that I am calling declare_weak with an
identifier tree structure instead of a decl tree structure.

Thanks, David


Index: c-pragma.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/c-pragma.c,v
retrieving revision 1.45
diff -c -p -r1.45 c-pragma.c
*** c-pragma.c	2001/08/31 19:27:12	1.45
--- c-pragma.c	2001/11/02 22:20:00
*************** handle_pragma_weak (dummy)
*** 282,304 ****
       cpp_reader *dummy ATTRIBUTE_UNUSED;
  {
    tree name, value, x;
!   enum cpp_ttype t;
  
    value = 0;
  
!   if (c_lex (&name) != CPP_NAME)
      BAD ("malformed #pragma weak, ignored");
!   t = c_lex (&x);
!   if (t == CPP_EQ)
      {
!       if (c_lex (&value) != CPP_NAME)
  	BAD ("malformed #pragma weak, ignored");
!       t = c_lex (&x);
      }
!   if (t != CPP_EOF)
      warning ("junk at end of #pragma weak");
  
!   add_weak (IDENTIFIER_POINTER (name), value ? IDENTIFIER_POINTER (value) : 0);
  }
  #endif
  
--- 282,318 ----
       cpp_reader *dummy ATTRIBUTE_UNUSED;
  {
    tree name, value, x;
!   enum cpp_ttype t_name, t_value, t_x;
  
    value = 0;
  
!   t_name = c_lex (&name);
! 
!   if (t_name != CPP_NAME && t_name != CPP_STRING)
      BAD ("malformed #pragma weak, ignored");
!   if (t_name == CPP_NAME && !DECL_P (name))
!     BAD ("#pragma weak identifier not defined in compilation unit");
! 
!   t_x = c_lex (&x);
!   if (t_x == CPP_EQ)
      {
!       t_value = c_lex (&value);
!       /* Name and value must both be identifier or string.  */
!       if (t_value != CPP_NAME && t_value != CPP_STRING && t_value != t_name)
  	BAD ("malformed #pragma weak, ignored");
!       if (t_value == CPP_NAME && !DECL_P (value))
! 	BAD ("#pragma weak identifier not defined in compilation unit");
! 
!       t_x = c_lex (&x);
      }
!   if (t_x != CPP_EOF)
      warning ("junk at end of #pragma weak");
  
!   if (t_name == CPP_NAME)
!     declare_weak (name, value);
!   else
!     add_weak (IDENTIFIER_POINTER (name),
! 	      value ? IDENTIFIER_POINTER (value) : 0);
  }
  #endif