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authorThomas Schwinge <thomas@schwinge.name>2011-11-30 16:54:25 +0100
committerThomas Schwinge <thomas@schwinge.name>2011-11-30 16:54:25 +0100
commit06b13cd7d45923b1f08d939935f1c213416186ef (patch)
treecae52d8d588f9481578d981c02a7109cb5b192b6 /open_issues/glibc/t/tls.mdwn
parent75bc54c39f371a464e6f8b7ad3bb0891cea1b28e (diff)
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+[[!meta copyright="Copyright © 2011 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
+document under the terms of the GNU Free Documentation License, Version 1.2 or
+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
+License|/fdl]]."]]"""]]
+
+[[!tag open_issue_glibc open_issue_libpthread]]
+
+# To Do
+
+ * Discuss d2431f633e6139a62e1575ec18830f7e81160cf0 with Samuel.
+
+ * `TLS_INIT_TP_EXPENSIVE` is unused; Hurd def. can be removed.
+
+
+# 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).
+ <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 :)