15 Feb
2005
15 Feb
'05
7:39 p.m.
Boaz Harrosh wrote:
> Danny Smith wrote:
>
>> Boaz Harrosh wrote:
>>
>>
>>> [Q] I'm (well ATL is) using __attribute__((weak)) (translated from
>>> __declspec( selectany) ) for instantiation of members and variables in
>>> headers. I had no problem with it On GCC in Linux (gcc 3.2.2). On MinGW
>>>
>>>
>>
>> IMAGE_COMDAT_SELECT_ANY is not quite same as PECOFF version of "weak" ,
but
>> AFAICT is equivalent to the GCC section flag ".linkonce discard". I
don't
>> think there is a way for the user to specify that for data using an
>> attribute, but it could be done with asm statements.
>>
>> .weak directive is partially supported in current binutils CVS.
>> __attribute__((weak)) is not supported by GCC-3.4.x but will be in the next
>> major GCC release (4.0.0).
>>
Sorry, that was unclear. I should have qualified with "on windows
targets"
>> The semantics of weak for PECOFF differ from
that on Linux.See the PECOFF60
>> specs (Microsoft Portable Executable and Common Object File Format
>> Specification) section on weak externals
>>
>> Danny
>>
>>
> (binutils at sources dot redhat dot com please also cc me as I'm not on
> the list)
>
> Attached is a proof (See fooInt.h) that gcc (gcc version 3.2 (mingw
> special 20020817-1)) has support for weak symbols. Just not with the
> regular syntax.
> But when templates are used duplicate symbols are merged by the linker.
>
> What would be the assembler magic to cram into the __WEAK__ definition
> that would make this project link?
>
I am currently testing a patch to GCC to add an __attribute__ ((selectany)) that
would work the way it is discribed in MS docs and in the spec of
IMAGE_COMDAT_SELECT_ANY in PECOFF doc. Basically it puts the symbol into its
own section with ".linkonce discard" charcteristics.
__declspec (selectany) int foo = 1;
becomes:
.globl _foo
.section .data$foo,"w"
.linkonce discard
.align 4
_foo:
.long 1
So far the only problem I've seen is that, although it works for global objects
with non-trivial constructors
eg:
struct X {
static int s;
int m;
X(int _i) : m(_i) {
m++;
}
};
__declspec(selectany) int X::s = -1; // OK
__declspec(selectany) X x(1); // This is OK but app will be bloated with
// duplicate initialization code.
.
I haven't figured out how to get rid of the duplicated inititialization code
I will submit the patch for comment once GCC trunk branches.
Danny
Free Life
Boaz