Messages in this thread | | | From | Florian Weimer <> | Subject | Re: [PATCH 1/5] glibc: Perform rseq(2) registration at C startup and thread creation (v10) | Date | Wed, 12 Jun 2019 16:22:55 +0200 |
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* Mathieu Desnoyers:
>> It's the registration from libc.so which needs some care. In >> particular, we must not override an existing registration. > > OK, so it could check if __rseq_abi.cpu_id is -1, and only > perform registration if it is the case. Or do you have another > approach in mind ?
No, __rseq_abi will not be shared with the outer libc, so the inner libc will always see -1 there, even if the outer libc has performed registration.
libio/vtables.c has some example what you can do:
/* In case this libc copy is in a non-default namespace, we always need to accept foreign vtables because there is always a possibility that FILE * objects are passed across the linking boundary. */ { Dl_info di; struct link_map *l; if (!rtld_active () || (_dl_addr (_IO_vtable_check, &di, &l, NULL) != 0 && l->l_ns != LM_ID_BASE)) return; }
_IO_vtable_check would have to be replaced with your own function; the actual function doesn't really matter.
The rtld_active check covers the static dlopen case, where rtld_active () is false in the inner libc.
Thanks, Florian
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