[lldb-dev] question about link_map data structure in elf on 64-bit Linux systems

Steve Pucci spucci at google.com
Sat Feb 1 08:37:19 PST 2014

Hi all,

I'm trying to determine if some code in DynamicLoaderPOSIXDYLD is correct
and I could use some confirmation:

The code in question reads the module id of a module as part of finding the
TLS block associated with that module, by determining its location and then
reading with a hardcoded 32-bit unsigned read.  (The code in question is
source/Plugins/DynamicLoader/POSIX-DYLD/DynamicLoaderPOSIXDYLD.cpp, in

I've read http://dev.gentoo.org/~dberkholz/articles/toolchain/tls.pdf ,
which describes a number of architectures and in all cases the value seems
to be either size_t or "unsigned long int".  Thus the code appears to be
wrong in at least some cases, in that it should be reading 64 bits when
debugging 64-bit runtimes.  The code presumably works today for 64-bit LSB
(little-endian) systems (which is most of the 64-bit Linuxes) because it's
reading the right 32-bits out of the 64-bit location.

But I'm not 100% sure, because
* I'm not sure that the referenced pdf is definitive
* I don't have an MSB 64-bit system to test on to verify that it's a bug.

Can anyone with any familiarity with this issue comment on this?

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