open_issues/glibc_tls_segment_tcbhead_t_dtv_offset.mdwn


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[[!tag open_issue_glibc]]

IRC, unknown channel, unknown date.

    <youpi> you can hardcode DTV_OFFSET as 4 for now
    <youpi> it's the offset of the dtv field in the tcbhead_t structure from hurd/libpthread
    <tschwinge> youpi: May very well be that I'm misunderstanding something, but wouldn't it rather be the offset of tcb in __pthread + the offset of dtv in tcbhead_t (which indeed is 4)?
    <youpi> what you don't know is that DTV_OFFSET is not relative to __pthread, but to the tls segment
    <tschwinge> Oh, aha.  Thanks.
    <youpi> and drepper abused the fact that in nptl __pthread appears at the start of the tls segment

kFreeBSD, glibc:

    ++#if 0
    + DTV_OFFSET                    offsetof(struct pthread, header.dtv)
    ++#else
    ++DTV_OFFSET                      offsetof(struct _pthread_descr_struct, p_header.data.dtvp)
    ++#endif