Hi,
I'm doing the unusual task of converting some c++ code into a FreeBSD
kernel module. Now all has been going great, and thus far I've been
able to debug quite a bit of it using printfs. However, I decided to
start using a kernel debugger, and to make this easier I passed g++
the –O0 flag, to make it compile without optimisations.
Bang, I hit a problem. All of a sudden when using the –O0 my module
wouldn't load because it was missing an undefined reference to
memmove. I found the specific object file which was using memmove. I
did that by doing objdump –t *.o and finding which file had an
undefined symbol memmove. Once I found the object file I grepped the
associated source and I was sure I was not using memmove. I then got
gcc to output both the post-processed source, as well as the asm.
The .ii file (post-processed source) did NOT mention memmove at all.
So I found it very odd that an undefined symbol existed in the object
file. So then I looked in the .s file (asm), and it was clearing
making a single call to memmove.
So after a few hours of pulling my hair out I found this in the gcc manual:
"-nostdlib .... The compiler may generate calls to memcmp, memset,
memcpy and memmove. These entries are usually resolved by entries in
libc. These entry points should be supplied through some other
mechanism when this option is specified."
So it appears that gcc may add calls to those four functions even if
you don't use them yourself? I assume this has not been a problem for
anyone yet due to only crazy people trying to use c++ in the kernel,
and the specific set of gcc options I'm using.
For the moment I have fixed this problem now by defining my own memmove like so:
extern "C" void * memmove(void * dst, const void * src, size_t len) {
bcopy(src, dst, len);
return dst;
}
But I was wondering if those four functions should be defined in the
kernel? I notice that memcpy and memset are already defined by the
kernel somewhere, so perhaps memmove and memcmp should join them?
Oh I should mention this was happening with the default gcc under FreeBSD 7.1.
Thanks
Andrew
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