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Diffstat (limited to 'open_issues/glibc_init_first.mdwn')
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diff --git a/open_issues/glibc_init_first.mdwn b/open_issues/glibc_init_first.mdwn new file mode 100644 index 00000000..774b7828 --- /dev/null +++ b/open_issues/glibc_init_first.mdwn @@ -0,0 +1,78 @@ +[[!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! |