libgloss/warning.h: adjust link_warning construct to modern gcc, gas and ld

[Jeff Johnston]

Patch checked in.  Thanks again.

-- Jeff J.

Hans-Peter Nilsson wrote:
> I noticed I didn't get the expected warnings at link time.  I
> looked at warning.h, and noticed that __SYMBOL_PREFIX wasn't
> used.  I fixed that.
> 
> After that, I got a warning, but without the specified message:
> /home/hp/cvs_areas/combined/cris-obj/cris-unknown-elf/./newlib/libc.a(makebuf.o):
> In function `__smakebuf':^M
> /home/hp/cvs_areas/combined/combined/newlib/libc/stdio/makebuf.c:96: warning: ^M
> 
> (empty line above; empty message)
> So I looked at the assembly code that GCC as of CVS "Fri Jan 14
> 01:28:39 UTC 2005" generates.  I noticed that the static const
> char[] isn't emitted at all!  Well, that's a valid optimization,
> since to GCC it's apparently unused!  I fixed that by adding the
> "used" attribute to the char[].
> 
> After that, I got assembler messages:
> isatty.s: Assembler messages:
> isatty.s:12: Warning: ignoring changed section type for .gnu.warning._isatty
> isatty.s:12: Warning: ignoring changed section attributes for .gnu.warning._isatty
> 
> I looked at warning.h again and noticed the
> make_section_unallocated hack; emitting a ".section
> .gnu.warning.symname" before the char symname[].  That is,
> mentioning the section name once before first use, without
> attributes and allocation letters, apparently in an attempt to
> cause later specifications; specifically allocation
> specification, to be ignored.  A brief look at ld history shows
> that this was necessary a long long time ago, but now the linker
> arranges to throw away .gnu.warning.* sections.  (The
> make_section_unallocated hack is benevolent, but nevertheless
> it's a redundant hack and the assembler messages may confuse
> users.)
> 
> I suggest just removing the make_section_unallocated hack, as
> per the following patch, which actually works.  (I also
> inspected the binary of a program where a linker message had
> been emitted to make sure there was no such string.  The local
> symbol is there, but not the string contents.)
> 
> 2005-01-16  Hans-Peter Nilsson  <hp@axis.com>
> 
> 	* libnosys/warning.h (link_warning) [HAVE_GNU_LD and HAVE_ELF]:
> 	Prefix symbol in section name with __SYMBOL_PREFIX.  Do not use
> 	__make_section_unallocated.  Mark magic variable as used.
> 
> Index: warning.h
> ===================================================================
> RCS file: /cvs/src/src/libgloss/libnosys/warning.h,v
> retrieving revision 1.3
> diff -c -p -r1.3 warning.h
> *** warning.h	15 Jan 2005 00:17:51 -0000	1.3
> --- warning.h	16 Jan 2005 18:46:17 -0000
> ***************
> *** 17,25 ****
>   
>   #  ifdef HAVE_SECTION_ATTRIBUTES
>   #   define link_warning(symbol, msg)                     \
> -   __make_section_unallocated (".gnu.warning." #symbol)  \
>     static const char __evoke_link_warning_##symbol[]     \
> !     __attribute__ ((section (".gnu.warning." #symbol))) = msg;
>   #  else
>   #   define link_warning(symbol, msg)
>   #  endif
> --- 17,25 ----
>   
>   #  ifdef HAVE_SECTION_ATTRIBUTES
>   #   define link_warning(symbol, msg)                     \
>     static const char __evoke_link_warning_##symbol[]     \
> !     __attribute__ ((section (".gnu.warning." __SYMBOL_PREFIX #symbol), \
> ! 		   __used__)) = msg;
>   #  else
>   #   define link_warning(symbol, msg)
>   #  endif
> 
> brgds, H-P