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

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.


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)

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