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authorThomas Schwinge <thomas@schwinge.name>2011-10-15 12:22:01 +0200
committerThomas Schwinge <thomas@schwinge.name>2011-10-15 12:22:01 +0200
commit080e7638c9c1b626b041594ca774bf4a7de4301f (patch)
tree6c7a3b7769138e76203e9fcb0a75fd1828f4a477 /open_issues/glibc_init_first.mdwn
parenta8e650d27aa54a83986a1cd7fca5607498aeab70 (diff)
open_issues/glibc: t/init-first.c.
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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]]
-
-IRC, freenode, #hurd, 2011-07-22
-
- [additional init-first.c patch]
- < tschwinge> civodul: The only thing I wonder about: Roland also once had
- done similar changes, which I then found they didn'T work with GCC 4.1,
- and backed them out in 08f53ee9d265ffdc7e0affd6acf346cceeb65559 and fixed
- the issue differently in d8d27e633a7860b37fd2e3142822b640a066cc0f (and
- e17cef66140d4c97710ea88bd8d12612799e1e0f). Have you reviewed this?
- < tschwinge> That's in the Savannah glibc repository.
- < tschwinge> And this has been in 2007, four years ago. I don't remember
- all the details.
- < tschwinge> And here is quite a good summary of this stuff, from
- init-first.c:
- < tschwinge> /* XXX This is all a crock and I am not happy with it.
- < tschwinge> This poorly-named function is called by static-start.S,
- < civodul> braunr: thanks; i must admit it took me a while to figure it out
- ;-)
- < tschwinge> which should not exist at all. */
- < tschwinge> civodul: I can imagine... :-/
- < civodul> tschwinge: re Roland's changes, that's weird; i plan to try to
- reinstate his change and see if it works
- < civodul> now, i won't test with GCC 4.1...
- < tschwinge> Yeah...
- < tschwinge> I'm happy if it works with 4.4 onwards.
- < tschwinge> civodul: And it's safe (in GCC terms) to write to ``* ((void
- **) __builtin_frame_address (0) + 1)'', and similar?
- < tschwinge> Or should we be coding this few stuff in assembly?
- < civodul> tschwinge: well, we should add a compile-time assertion for
- __builtin_return_address (0) == *((void**)__builtin_frame_address (0) +
- 1)
- < civodul> (i think GCC can figure it out at compile-time)
- < civodul> but on IA32 it should always be true
- < civodul> what's the name of glibc's compile-time assert macro already?
- < tschwinge> I wonder whether that might interfere with some of GCC's
- optimizations?
- < civodul> what?
- < tschwinge> Well, it seems unclean for me to be modifying a function's
- return address from within C code.
- < tschwinge> civodul: I added a verify.h in the t/verify.h branch. But
- people didn't really like it too much. They rather wanted to directly
- inline the array[(cond)?1:-1] code.
- < civodul> ok
- < civodul> i remember a debate about Gnulib's verify.h
- < civodul> i thought something comparable had landed eventually
- < tschwinge> civodul: Oh, maybe I missed it.
- < tschwinge> civodul: In init-first.c:init, what about the usage of
- data[-1] in the else path (not using cthreads) -- is that good as-is?
- < civodul> tschwinge: oooh, it probably needs to fixed too
- < civodul> but i haven't reached that point yet ;-)
- * civodul tries to cross-bootstrap GNU from scratch
- < tschwinge> civodul: I'd be happy to learn what was wrong with Roland's
- original idea of fixing this. Or perhaps this was a GCC 4.1 bug? Or
- perhaps GCC was inlining to much, and then got confused with frames and
- return addresses?
- < civodul> tschwinge: Roland's change looks good to me, so it could have
- been a GCC bug
- < civodul> tschwinge: OK to commit the patch to t/init-first.c (with both
- data[-1] replaced)?
- < tschwinge> civodul: OK, if you are confident that it works with GCC 4.4
- onwards. If yes, please add your changelog snippet to .topmsg, and also
- add a not that Roland's original code may in fact have been fine, and we
- may have hit a compiler bug.
- < civodul> tschwinge: OK, will do
- < civodul> tschwinge: though regarding Roland's change, i'd prefer to
- actually test and see
- < tschwinge> civodul: Thanks!