Date: Wed, 09 Feb 2022 21:44:13 +0100 From: Florian Weimer <fweimer@...hat.com> To: Rich Felker <dalias@...c.org> Cc: Yehuda Yitchak <yehuda80@...il.com>, musl@...ts.openwall.com Subject: Re: Accessing Thread-Local-Storage in GDB * Rich Felker: > On Wed, Feb 09, 2022 at 09:32:10AM +0200, Yehuda Yitchak wrote: >> Hello >> >> one of the applications i am debugging is compiled using MUSL libc >> (aarch64) Version 1.1.19 >> when i inspect a core-dump and try to view TLS variables with "print >> __percpu_dev" gdb (v8.3) complains: >> >> Cannot find thread-local storage for LWP 22873, executable file >> <core-dump-file> >> Cannot find thread-local variables on this target >> >> Any idea how I can overcome this? >> Appreciate if you could CC me since i'm not subscribed. > > I think this is a consequence of gdb wanting to have a libthread_db (a > GNU- and Solaris-ism) to tell it how to interact with the threads > implementation of the process being debugged rather than just doing > things in a libpthread-agnostic way like musl wants it to do. I think > it should be fixable on the gdb side without too much headache, but I > don't know how. GDB would have to poke at libc internals and basically reimplement __tls_get_addr. Maybe something can be done by calling libc ABI functions for TLS access instead, but that doesn't work for core files. > As a workaround, if the program is dynamic-linked, you can do > something like print *(int *)dlsym(0, "foo") from the relevant thread > context and it should work. This only works if foo is a dynamic symbol (and if you aren't examining a coredump). My interest in initial-exec TLS (despite its impact on dlopen) is somewhat motivated by a desire to make things easier for debuggers. Thanks, Florian
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