----- On Nov 26, 2018, at 3:28 AM, Florian Weimer fweimer@xxxxxxxxxx wrote: > * Mathieu Desnoyers: > >> Using a "weak" symbol in early adopter libraries is important, so they >> can be loaded together into the same process without causing loader >> errors due to many definitions of the same strong symbol. > > This is not how ELF dynamic linking works. If the symbol name is the > same, one definition interposes the others. > > You need to ensure that the symbol has the same size everywhere, though. > There are some tricky interactions with symbol versions, too. (The > interposing libraries must not use symbol versioning.) I was under the impression that loading the same strong symbol into an application multiple times would cause some kind of warning if non-weak. I did some testing to figure out which case I remembered would cause this. When compiling with "-fno-common", dynamic and static linking work fine, but trying to add multiple instances of a given symbol into a single object fails with: /tmp/ccSakXZV.o:(.bss+0x0): multiple definition of `a' /tmp/ccQBJBOo.o:(.bss+0x0): first defined here Even if the symbol has the same size. So considering that we don't care about compiling into a single object here, and only care about static and dynamic linking of libraries, indeed the "weak" symbol is not useful. So let's make __rseq_abi and __rseq_refcount strong symbols then ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
