* Stefan Hajnoczi: > I've been trying to make the inline asm that gets the address of a TLS > variable for QEMU coroutines pass QEMU's GitLab CI. > https://gitlab.com/stefanha/qemu/-/blob/coroutine-tls-fix/include/qemu/coroutine-tls.h#L89 > > The code isn't -fPIC-friendly (R_X86_64_TPOFF32 relocations aren't > allowed in -fPIC shared libraries) so builds fail with ./configure > --enable-modules. While I was tackling this I stumbled on this: > > void *dst_ptr; > asm volatile("" : "=r"(dst_ptr) : "0"(&tls_var)) > > What's nice about it: > - It's portable, there are no arch-specific assembly instructions. > - It works for both -fPIC and non-PIC. > > However, I wonder if the compiler might reuse a register that already > contains the address. Then we'd have the coroutine problem again when > qemu_coroutine_yield() is called between the earlier address calculation > and the asm volatile statement. > > Thoughts?
Sorry, I don't see why this isn't equivalent to a plain &tls_var. What exactly are you trying to achieve? Thanks, Florian
