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From: "bugdal at aerifal dot cx" <sourceware-bugzilla@sourceware.org>
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Subject: [Bug dynamic-link/21050] Prevent tailcall optimizations of libdl
 functions
Date: Mon, 12 Oct 2020 15:25:49 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D21050

--- Comment #3 from Rich Felker <bugdal at aerifal dot cx> ---
The suggestion in comment 2 is a spec violation; it has a static identifier
dlsym in place of the required extern one, and also breaks the identity of
function pointers (different pointer per translation unit). You have to use
function-like macros to do this kind of thing in a conforming way, and the
macro still does not cover the case where the caller undefines the macro or
directly calls the function via its address.

I believe the right solution is to deprecate the old constant value of
RTLD_NEXT and instead define RTLD_NEXT to expand to the address of a static
anchor object inside the translation unit. The dynamic linker can then use =
that
anchor object, rather than the return address, to identify the DSO from whi=
ch
it was called. This also fixes a lot of other usage patterns, e.g. where
library A calls dlsym_wrapper(RTLD_NEXT, "foo") and dlsym_wrapper is define=
d in
library B.

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