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[[!meta copyright="Copyright © 2011, 2012, 2013 Free Software Foundation,
Inc."]]
[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable
id="license" text="Permission is granted to copy, distribute and/or modify this
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any later version published by the Free Software Foundation; with no Invariant
Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license
is included in the section entitled [[GNU Free Documentation
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[[!tag open_issue_glibc open_issue_libpthread]]
# To Do
* Discuss d2431f633e6139a62e1575ec18830f7e81160cf0 with Samuel.
* Validate our implementation against
<https://sourceware.org/glibc/wiki/TLSandSignals>.
# Documentation
[[!taglink open_issue_documentation]]
* IRC, freenode, #hurd, 2011-11-26
<tschwinge> In glibc multiarch support (strcasecmp for i686 SSE3, etc.)
there is access to memory via gs: -- this will need to be changed for
us, right?
<youpi> depends on the access
<tschwinge> * `optimized strcasecmp and strncasecmp for x86-32`
(multiarch),
<tschwinge> 76e3966e9efc3808a9e7ad09121c5dfc1211c20b +
<tschwinge> 6abf346582ba678f4850a88b4a5950593841df1d +
<tschwinge> 5583a0862cf94f71cbcde91c4043a20af65facca. `gs`
access.
<youpi> + movl __libc_tsd_LOCALE@GOTNTPOFF(%ebx), %eax
<youpi> that's handled by the linker fine
<youpi> it's only the things held in the tcb_t structure which can pose
problem
<tschwinge> tcbhead_t?
<tschwinge> I'm looking at this.
<tschwinge> So, at gs:0, there is the TCB.
<tschwinge> And we have the same layout as NPTL/Linux, just that we
don't have as much data there as they have.
<tschwinge> We're missing multiple_threads, sysinfo, sttack_guard,
pointer_guard, gscope_flag, private_futex, __private_tm[5].
<tschwinge> So, if one of these is referenced (be it my name or by
numeric offset), this is invalid for us.
<tschwinge> Anything else should work equivalently.
<youpi> yes
<youpi> usually the only numeric offset being used is 0
<youpi> so it would simply not build
<tschwinge> And the other offsers are generated via tcb-offsets.sym.
<tschwinge> glibc's elf/stackguard-macros.h is wrong for us (but not
used anywhere apart from elf/tst-stackguard1.c, I think).
After commit a9538892adfbb9f092e0bb14ff3a1703973968af, it's
`sysdeps/i386/stackguard-macros.h`; problem remains.
<tschwinge> __thread __locale_t __libc_tsd_LOCALE = &_nl_global_locale;
-- this means that a __libc_tsd_LOCALE values will be in the TLS
segment, and this is what is being accessed from the assembler code
with %gs:__libc_tsd_LOCALE@NTPOFF, and the linker will resolve this.
<youpi> yes
<youpi> see in the nm output, the libc_tsd symbols
<youpi> these provide the offsets
<tschwinge> youpi: Thank you, I'm now understanding this part of TLS
much better.
<youpi> have you had a look at the tls.pdf from Uli ?
<youpi> all the gory details are there :)
Commit c61b4d41c9647a54a329aa021341c0eb032b793e, [[!sourceware_PR 15754]], adds
`sysdeps/i386/stackguard-macros.h:POINTER_CHK_GUARD`, which is not correct for
us (at the moment), but it also shouldn't cause any harm, as this file is only
used in `elf/tst-ptrguard1.c` and `elf/tst-stackguard1.c`, which now will fail
to build for us, as we don't have a `pointer_guard` member in
`sysdeps/mach/hurd/tls.h:tcbhead_t`.
We don't define `THREAD_SET_POINTER_GUARD`.
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