On Tue, Aug 13, 2013 at 9:42 PM, Jakub Jelinek <ja...@redhat.com> wrote:
> We right now ICE with -mcmodel=large -fpic on x86_64 on TLS GD and LD > sequences, because obviously we can't call __tls_get_addr@plt there from code > potentially more than 2GB away from the PLT slot. > > The attached patches add support for that in gcc and also teaches linker > about those, because otherwise the linker will fail if you try to link such > -mcmodel=large -fpic code into binaries or PIEs. > > To make transitions possible, we emit always > leaq foo@tlsgd(%rip), %rdi > movabsq $__tls_get_addr@pltoff, %rax > addq $rbx, %rax > call *%rax > resp. > leaq foo@tlsld(%rip), %rdi > movabsq $__tls_get_addr@pltoff, %rax > addq $rbx, %rax > call *%rax > sequences (22 bytes, 6 bytes longer than what we do for TLSGD for normal > libraries). > > Bootstrapped/regtested on x86_64-linux and i686-linux, attached is also the > sources I've used to test all the 3 different transitions. > > Ok for trunk and 4.8 branch (and binutils trunk)? The implementation for x86 is technically OK, but I wonder if these sequences should be documented in some authoritative document about TLS relocations. The "ELF Handling For Thread-Local Storage" document [1] doesn't mention various code models fo x86_64, so I was not able to cross-check the implementaton vs. documentation. [1] http://www.akkadia.org/drepper/tls.pdf Thanks, Uros.
