The fact that it works on Linux, means that the 'bug' (the compiler linking against an extern symbol, even when declared localy) exists on almost all current versions of gcc / binutils...
Could be an interesting bug to fix, but should not _really_ be a problem, as it is unlikely to be triggered in good code.
Thanks, -justin
H. Henning Schmidt wrote:
I have discovered what may be a bug in the linker/relocater in cygwin (or, more likely, I am doing something stupid again).
When I use a structure containing function pointers, and this structure is placed in an archive, then the function pointer becomes NULL. As an example, compile the attached files as follows:
gcc -O2 -Wall -c inc.c ar rsvc inc.a inc.c gcc -O2 -Wall -o test test.c inc.a
Executing test.exe prints 0x0 (the address of the function cointained in the structure), and subsequently segfaults.
Relinking with
gcc -O2 -Wall -o test test.c inc.o
produces a binary that works correctly.
It seems that once the object file is archived, the dynamic loader losses the capability of correctly assigning the function addresses?
Any help would be greatly appreciated.
You are constructing two instances of type <struct js>. One as global static member of the module <inc>, and another instance in module <test>. The one in module <inc> gets initalized (i.e. func pointer is set to address of local func <junk>), the other one remains uninitialized. Both of these instances of type <struct js> are named <jsi> ... which is certainly a little confusing. AFAIK, the code in main() should always and only reference the local instance (the uninitialized one from module <test>), which would result in an output of either 0x0 (or any other random number, really ... this is just reading unitialized memory).
To my understanding, the fact that your second linker invocation (direct linking, no static archive involved) does use the static (and thus presumably invisible) instance of <struct js> from the <inc> module does indicate a (completely different) bug in the linker ...
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