Re: Fix -fsection-anchors on Darwin

[Jack Howarth <howarth at bromo dot med dot uc dot edu>]

On Wed, Apr 14, 2010 at 11:47:09AM -0400, Jack Howarth wrote:
> On Thu, Jun 08, 2006 at 03:44:20PM -0700, Mike Stump wrote:
> > Well, given the time and the wrong code gen, I've disabled -fsection- 
> > anchors for darwin.  It is safer than doing things like disappearing  
> > data on people, which is the direction Geoff wanted to go.  I think we 
> > need a new linker feature for multiple entry points to really make this 
> > work well, and if not that, then turning off subsections_via_symbols and 
> > ensuring that works well.
> 
> Mike,
>    Could you update your comments on this? Since it seems unlikely
> that the linker will ever been changed on darwin to support section-anchors,
> it seems to leave on the turning off subsections_via_symbols if we
> wanted to implement section-anchors support on darwin, no?
> 

This openradar seems to discuss disabling subsections_via_symbols in the
assembly file but doesn't indicate how to do it from within the compiler...

http://openradar.appspot.com/7201596


> >
> > If the optimizer wants to jam all the data together into one object  
> > itself, and then write out that object, that would work as well, and  
> > there is something appealing about that.  Also, to get nice codegen and 
> > dead code stripping, I think we want LTO to manage this issue.
> 
> Since it appears that Mach-O LTO will be possible, I assume this can
> be handled through that option.
>                    Jack
> 
> >
> > This fixes a regression introduced by:
> >
> > 2006-04-30  David Edelsohn  <edelsohn@gnu.org>
> >
> >         * config/rs6000/rs6000.c (rs6000_override_options): Enable
> >         TARGET_NO_FP_IN_TOC for section anchors.
> >         (optimization_options): Enable section anchors for all
> >         non-"Objective" languages.
> >
> 
> > 2006-06-08  Mike Stump  <mrs@apple.com>
> > 
> > 	PR target/26427
> > 	* config/darwin.c (darwin_asm_output_anchor): Disable
> > 	-fsection-anchors on darwin for now.
> > 	* config/darwin.h (TARGET_ASM_OUTPUT_ANCHOR): Likewise.
> > 	* rs6000/rs6000.c (optimization_options): Likewise.
> > 
> > 	PR target/26427
> > 	* gcc.dg/pr26427.c: Test to ensure that -fsection-anchors doesn't
> > 	produce bad code on darwin.
> > 
> > Doing diffs in .:
> > --- ./config/darwin.c.~1~	2006-06-06 05:36:45.000000000 -0700
> > +++ ./config/darwin.c	2006-06-08 14:52:31.000000000 -0700
> > @@ -1524,6 +1524,8 @@ darwin_binds_local_p (tree decl)
> >    return default_binds_local_p_1 (decl, 0);
> >  }
> >  
> > +#if 0
> > +/* See TARGET_ASM_OUTPUT_ANCHOR for why we can't do this yet.  */
> >  /* The Darwin's implementation of TARGET_ASM_OUTPUT_ANCHOR.  Define the
> >     anchor relative to ".", the current section position.  We cannot use
> >     the default one because ASM_OUTPUT_DEF is wrong for Darwin.  */
> > @@ -1536,6 +1538,7 @@ darwin_asm_output_anchor (rtx symbol)
> >    fprintf (asm_out_file, ", . + " HOST_WIDE_INT_PRINT_DEC "\n",
> >  	   SYMBOL_REF_BLOCK_OFFSET (symbol));
> >  }
> > +#endif
> >  
> >  /* Set the darwin specific attributes on TYPE.  */
> >  void
> > --- ./config/darwin.h.~1~	2006-06-06 05:36:45.000000000 -0700
> > +++ ./config/darwin.h	2006-06-08 14:52:31.000000000 -0700
> > @@ -812,8 +812,6 @@ enum machopic_addr_class {
> >  	goto DONE;									\
> >        }
> >  
> > -#define TARGET_ASM_OUTPUT_ANCHOR darwin_asm_output_anchor
> > -
> >  /* Experimentally, putting jump tables in text is faster on SPEC.
> >     Also this is needed for correctness for coalesced functions.  */
> >  
> > @@ -852,6 +850,7 @@ void add_framework_path (char *);
> >  #define TARGET_POSIX_IO
> >  
> >  /* All new versions of Darwin have C99 functions.  */
> > +
> >  #define TARGET_C99_FUNCTIONS 1
> >  
> >  #define WINT_TYPE "int"
> > @@ -859,7 +858,20 @@ void add_framework_path (char *);
> >  /* Every program on darwin links against libSystem which contains the pthread
> >     routines, so there's no need to explicitly call out when doing threaded
> >     work.  */
> > +
> >  #undef GOMP_SELF_SPECS
> >  #define GOMP_SELF_SPECS ""
> >  
> > +/* Darwin can't support anchors until we can cope with the adjustments
> > +   to size that ASM_DECLARE_OBJECT_NAME and ASM_DECLARE_CONSTANT_NAME
> > +   when outputting members of an anchor block and the linker can be
> > +   taught to keep them together or we find some other suitable
> > +   code-gen technique.  */
> > +
> > +#if 0
> > +#define TARGET_ASM_OUTPUT_ANCHOR darwin_asm_output_anchor
> > +#else
> > +#define TARGET_ASM_OUTPUT_ANCHOR NULL
> > +#endif
> > +
> >  #endif /* CONFIG_DARWIN_H */
> > --- ./config/rs6000/rs6000.c.~1~	2006-06-06 05:36:45.000000000 -0700
> > +++ ./config/rs6000/rs6000.c	2006-06-08 14:52:31.000000000 -0700
> > @@ -1633,7 +1633,7 @@ optimization_options (int level ATTRIBUT
> >    /* Enable section anchors by default.
> >       Skip section anchors for Objective C and Objective C++
> >       until front-ends fixed.  */
> > -  if (lang_hooks.name[4] != 'O')
> > +  if (!TARGET_MACHO && lang_hooks.name[4] != 'O')
> >      flag_section_anchors = 1;
> >  }
> >  
> > --- ./testsuite/gcc.dg/pr26427.c.~1~	2006-06-08 14:52:31.000000000 -0700
> > +++ ./testsuite/gcc.dg/pr26427.c	2006-06-08 14:54:07.000000000 -0700
> > @@ -0,0 +1,24 @@
> > +/* { dg-warning "this target does not support" } */
> > +/* { dg-do run { target { *-*-darwin* } } } */
> > +/* { dg-options { -fsection-anchors -O } } */
> > +/* PR target/26427 */
> > +
> > +struct a {};
> > +static const int d = 1;
> > +static const struct a b = {};
> > +static const int c = 1;
> > +int f(const int *, const struct a *, const int*, const int*);
> > +
> > +int g(void) {
> > +  return f(&c, &b, &d, &c);
> > +}
> > +
> > +int f(const int *b, const struct a *c, const int *d, const int *e) {
> > +  return *b == *d;
> > +}
> > +
> > +int main(void) {
> > +  if (!g())
> > +    __builtin_abort();
> > +  return 0;
> > +}
> > --------------
>