Hi, On 2021-11-24 17:55:03 -0500, Andrew Dunstan wrote: > On 11/24/21 13:55, Andres Freund wrote: > > On 2021-11-23 17:28:08 +0100, Peter Eisentraut wrote: > >> On 22.11.21 23:32, Tom Lane wrote: > >>>> The easier approach for this class of issues is to use the linker option > >>>> -Bsymbolic. > >>> I don't recall details, but we've previously rejected the idea of > >>> trying to use -Bsymbolic widely; apparently it has undesirable > >>> side-effects on some platforms. See commit message for e3d77ea6b > >>> (hopefully there's some detail in the email thread [1]). It sounds > >>> like you're not actually proposing that, but I thought it would be > >>> a good idea to note the hazard here. > >> Also, IIRC, -Bsymbolic was once frowned upon by packaging policies, since > >> it > >> prevents use of LD_PRELOAD. I'm not sure what the current thinking there > >> is, however. > > It doesn't break some (most?) of the uses of LD_PRELOAD. In particular, it > > doesn't break things like replacing the malloc implementation. When do you > > have a symbol that you want to override *inside* your library (executables > > already bind to their own symbols at compile time)? I've seen that for > > replacing buggy functions in closed source things, but that's about it? > > > > Which things does it break exactly?
-Bsymbolic causes symbols that are defined and referenced within one shared library to use that definition. E.g. if a shared lib has a function "do_something()" and some of its code calls do_something(), you cannot use LD_PRELOAD (or a definition in the main binary) to redirect the call to do_something() inside the shared library to something else. I.e. if a shared library calls a function that's *not* defined within that shared library, -Bsymbolic doesn't have an effect for that symbol. > I have a case where a library that > is LD_PRELOADed calls PQsetSSLKeyPassHook_OpenSSL() in its constructor > function. I'd be very unhappy if that stopped working (and so would our > client). Bsymbolic shouldn't affect that at all. Greetings, Andres Freund
