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Re: [Patch, mach-o/gas] correct a case where stub size is not filled in by GAS.
On Feb 9, 2012, at 4:26 PM, Iain Sandoe wrote:
> 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.
Ah, ok that's what I missed.
> 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.
well, we use an unsigned int for sectalign, which is large. So we could expanded the table without increasing memory footprint (if this is a concern).
So, it is OK.
Thank you for the extra comments.
>>> fixed thus:
>>> * 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)
>>> sizeof_stub = get_absolute_expression ();
>>> + specified_mask |= SECT_STUB_SPECIFIED;
>>> else if ((specified_mask & SECT_ATTR_SPECIFIED)
>>> && sectype == BFD_MACH_O_S_SYMBOL_STUBS)