> You find complete details about this approach in
> http://www.haible.de/bruno/woe32dll.html
>
<quote>
extern __declspec(dllimport) int externvar[5];
extern __declspec(dllimport) int externfunc(int);
int externfunc2 (int x)
{
return externvar[x] + externfunc (0);
}
int externvar[5] = { 11, 22, 33, 44, 55 };
int externfunc (int x)
{
if (x == 0)
return 42;
else
return externfunc2 (x);
}
extern __declspec(dllimport) int externvar[5];
extern __declspec(dllimport) int externfunc(int);
int externfunc2 (int x)
{
return externvar[x] + externfunc (0);
}
int externvar[5] = { 11, 22, 33, 44, 55 };
int externfunc (int x)
{
if (x == 0)
return 42;
else
return externfunc2 (x);
}
gcc reports warnings:
warning: 'externvar' defined locally after being referenced with
dllimport linkage
warning: 'externfunc' defined locally after being referenced with
dllimport linkage
Once libtool is changed to not cause link errors for self-references,
there is no need any more for this warning. gcc should remove this
warning.
</quote>
Are you sure about that.
The reason that gcc emits these warnings is this:
gcc -S dllimp.c
.file "dllimp.c"
.text
.globl _externfunc2
.def _externfunc2; .scl 2; .type 32; .endef
_externfunc2:
pushl %ebp
movl %esp, %ebp
pushl %ebx
subl $4, %esp
movl 8(%ebp), %edx
movl __imp__externvar, %eax <<< imported
movl (%eax,%edx,4), %ebx
movl $0, (%esp)
movl __imp__externfunc, %eax <<< imported
call *%eax
leal (%ebx,%eax), %eax
addl $4, %esp
popl %ebx
popl %ebp
ret
.globl _externvar <<< exported
.data
.align 4
_externvar:
.long 11
.long 22
.long 33
.long 44
.long 55
.text
.globl _externfunc <<< exported
.def _externfunc; .scl 2; .type 32; .endef
_externfunc:
pushl %ebp
movl %esp, %ebp
subl $8, %esp
cmpl $0, 8(%ebp)
jne L4
movl $42, -4(%ebp)
jmp L6
L4:
movl 8(%ebp), %eax
movl %eax, (%esp)
call _externfunc2
movl %eax, -4(%ebp)
L6:
movl -4(%ebp), %eax
leave
ret
There is dangerous ambiguity.
In the past this kind of ambiguity cause most of the dllimport-related
ICE's in GCC.
Does the client really want to resolve the two symbols using dllimport
semantics?
With unit-a-time optimizations, we delay adding the attribute until the
whole unit
is processed.
gcc -O2 -funit-at-a-time -S dllimp.c
.file "dllimp.c"
.text
.p2align 4,,15
.globl _externfunc
.def _externfunc; .scl 2; .type 32; .endef
_externfunc:
pushl %ebp
movl %esp, %ebp
movl 8(%ebp), %eax
testl %eax, %eax
jne L8
popl %ebp
movl $42, %eax
ret
.p2align 4,,7
L8:
popl %ebp
jmp _externfunc2
.p2align 4,,15
.globl _externfunc2
.def _externfunc2; .scl 2; .type 32; .endef
_externfunc2:
pushl %ebp
movl %esp, %ebp
subl $8, %esp
movl $0, (%esp)
call _externfunc
movl 8(%ebp), %edx
movl _externvar(,%edx,4), %ecx
leave
addl %ecx, %eax
ret
.globl _externvar
.data
.align 4
_externvar:
.long 11
.long 22
.long 33
.long 44
.long 55
which is probably what the user wanted.
Maybe not.
Maybe the user really just made a [im|ex] typo.
I think this is what MSVC compiler does, warning that dllimport has
been
replaced by dllexport.
You may be interested in the dllimport/export sematics used by the SH
symbian OS. See the comfig/gcc/sh/symbian.c for a quick overview.
There s a complete spec available on the web, but I've misplaced the
reference.
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