Re: [Patch, mach-o/gas] correct a case where stub size is not filled in by GAS.

[Iain Sandoe <developer at sandoe-acoustics dot co dot uk>]

On 9 Feb 2012, at 15:17, Tristan Gingold wrote:

> On Feb 9, 2012, at 3:28 PM, Iain Sandoe wrote:
>
> > the stub size for well-known-stub sections is not filled in from  
> > the BFD section translation table, but the other flags *are* when  
> > the section type is recognized.
> >
> > This leads to a failure to fill in the stub-size when someone  
> > specifies a well-known stub section by a hand-written section  
> > command. (e.g. darwin.S in libffi).
>
> Sorry, but I still do not understand the patch.  Maybe you should  
> quote the line in darwin.S if this is not this one:
>
> .section __IMPORT,__jump_table,symbol_stubs,self_modifying_code 
> +pure_instructions,5

that's the line.

> Currently, stub_size is always extracted from the .section (but  
> default to 0).  So currently it was set to 5.  What your patch  
> changes on darwin.S ?

the size is extracted correctly and passed to  
obj_mach_o_make_or_get_sect ().

However, when obj_mach_o_make_or_get_sect makes the section - it will  
be provided with default values for the attributes and flags by BFD  
[ which recognizes the section as a 'standard' one].  However, this  
does not include the stub-size, which is not part of our translation  
table at present.

Anyway, in obj_mach_o_make_or_get_sect () we then find that flags !=  
NO_FLAGS and so bypass the code that filled in the stub size.

> Also, I don't understand why stub_size is handled differently from  
> alignment.

Well, it seemed to expand the translation tables a lot for just a  
handful of cases .. it seemed like bloat... I guess we could revisit  
that.

Iain

> > fixed thus:
> >
> > gas:
> >
> > 	* config/obj-macho.c (obj_mach_o_make_or_get_sect): Always fill in  
> > stub size
> > 	when provided.  (obj_mach_o_section): Flag that stub-size has been  
> > provided.
> >
> > diff --git a/gas/config/obj-macho.c b/gas/config/obj-macho.c
> > index ba09780..17a21e6 100644
> > --- a/gas/config/obj-macho.c
> > +++ b/gas/config/obj-macho.c
> > @@ -168,6 +168,7 @@ obj_mach_o_get_section_names (char *seg, char  
> > *sec,
> > #define SECT_TYPE_SPECIFIED 0x0001
> > #define SECT_ATTR_SPECIFIED 0x0002
> > #define SECT_ALGN_SPECIFIED 0x0004
> > +#define SECT_STUB_SPECIFIED 0x0008
> >
> > static segT
> > obj_mach_o_make_or_get_sect (char * segname, char * sectname,
> > @@ -267,7 +268,6 @@ obj_mach_o_make_or_get_sect (char * segname,  
> > char * sectname,
> >
> >      msect->align = secalign;
> >      msect->flags = sectype | secattr;
> > -      msect->reserved2 = stub_size;
> >
> >      if (sectype == BFD_MACH_O_S_ZEROFILL
> > 	  || sectype == BFD_MACH_O_S_GB_ZEROFILL)
> > @@ -280,6 +280,10 @@ obj_mach_o_make_or_get_sect (char * segname,  
> > char * sectname,
> > 	as_warn (_("Ignoring changed section attributes for %s"), name);
> >    }
> >
> > +  if (specified_mask & SECT_STUB_SPECIFIED)
> > +    /* At present, the stub size is not supplied from the BFD  
> > tables.  */
> > +    msect->reserved2 = stub_size;
> > +
> >  return sec;
> > }
> >
> > @@ -413,6 +417,7 @@ obj_mach_o_section (int ignore ATTRIBUTE_UNUSED)
> >
> > 	      input_line_pointer++;
> >              sizeof_stub = get_absolute_expression ();
> > +              specified_mask |= SECT_STUB_SPECIFIED;
> >            }
> >          else if ((specified_mask & SECT_ATTR_SPECIFIED)
> > 		   && sectype == BFD_MACH_O_S_SYMBOL_STUBS)