Re: Basesystem programs redefine routine symbols from libc

[David Young <dyoung%pobox.com@localhost>]

On Sat, Dec 09, 2017 at 03:46:42PM +0100, Kamil Rytarowski wrote:
> I'm testing LLVM sanitizers. Right now, not every one is compatible
> as-is, because there are linker issues. The sanitizers redefine symbols
> for routines in libc like uname(3) in order to sanitize it with internal
> logic. However there exist programs in the basesystem that shadow libc
> symbol routines as well, for example ps(1):
> 
> bin/ps/extern.h:void    uname(struct pinfo *, VARENT *, enum mode);
> bin/ps/keyword.c:      VAR4("user", "USER", LJUST, uname),
> bin/ps/print.c:uname(struct pinfo *pi, VARENT *ve, enum mode mode)

Hi Kamil,

I am curious where this redefinition occurs.

For example, does an LLVM pass look for calls to `uname` and rewrite
them to call `intercept_uname`?  In that case, it seems like it could
check the number & type of parameters and then skip the rewriting if
there was not a match.

Or does some symbol rewriting trickery---perhaps with objcopy, ld, or
the moral equivalent---perform the rewriting?

I was under the impression that at least part of the LLVM-tsan rewriting
was done using the dlsym() tricks, but a badly out-of-date LLVM-tsan may
have made that impression. :-) Or maybe you're talking about one of the
other sanitizers.

Dave

-- 
David Young
dyoung%pobox.com@localhost    Urbana, IL    (217) 721-9981