diff options
Diffstat (limited to 'open_issues/glibc')
| -rw-r--r-- | open_issues/glibc/mremap.mdwn | 163 |
1 files changed, 5 insertions, 158 deletions
diff --git a/open_issues/glibc/mremap.mdwn b/open_issues/glibc/mremap.mdwn index a293eea0..874c7ae0 100644 --- a/open_issues/glibc/mremap.mdwn +++ b/open_issues/glibc/mremap.mdwn @@ -10,177 +10,24 @@ License|/fdl]]."]]"""]] [[!tag open_issue_glibc]] -[[!toc]] - +The Hurd does not currently support the `mremap` function. -# binutils gold +For the `MREMAP_MAYMOVE` case it is easy to work around; see +`[binutils]/gold/mremap.c`, for example. -## IRC, freenode, #hurd, 2011-01-12 - - <teythoon> I've been looking into building gold on hurd and it built fine - with one minor tweak - <teythoon> and it's working fine according to its test suite - <teythoon> the only problem is that the build system is failing to detect - the hurdish mremap which lives in libmemusage - <teythoon> on linux it is in the libc so the check succeeds - <teythoon> any hints on how to fix this properly? - <antrik> hm... it's strange that it's a different library on the Hurd - <antrik> are the implementations compatible? - <teythoon> antrik: it seems so, though the declarations differ slightly - <antrik> I guess the best thing is to ask on the appropriate list(s) why - they are different... - <teythoon> teythoon@ganymede:~/build/gold/binutils-2.21/gold$ grep -A1 - mremap /usr/include/sys/mman.h - <teythoon> extern void *mremap (void *__addr, size_t __old_len, size_t - __new_len, int __flags, ...) __THROW; - <teythoon> vs - <antrik> of course it would be possible to modify the configure script to - check for the Hurd variant too; but first we should establish whether - here is actually any reason for being different, or it's just some - historical artefact that should be fixed... - <teythoon> teythoon@ganymede:~/build/gold/binutils-2.21/gold$ fgrep 'extern - void *mremap' mremap.c - <teythoon> extern void *mremap (void *, size_t, size_t, int, ...); - <teythoon> the problem is that the test fails to link due to the fact that - mremap isn't in the libc on hurd - <antrik> yeah, it would be possible for the configure script to check - whether it works when the hurdish extra library is added explicitely - <antrik> but again, I don't see any good reason for being different here in - the first place... - <teythoon> so should I create a patch to move mremap? - <antrik> if it's not too complicated, that would be nice... it's always - easier to discuss when you already have code :-) - <antrik> OTOH, asking first might spare you some useless work if it turns - out there *is* some reason for being different after all... - so where is the right place to discuss this? - <antrik> bug-hurd mailing list and/or glibc mailing list. not sure which - one is better -- I guess it doesn't hurt to crosspost... +[[!toc]] -[[mailing_lists/libc-alpha]] is the correct list, and cross-posting to -[[mailing_lists/bug-hurd]] would be fine, too. - <teythoon> antrik: some further digging revealed that mremap belongs to - /lib/libmemusage.so on both hurd and linux - <teythoon> the only difference is that on linux there is a weak reference - to that function in /lib/libc-2.11.2.so - <teythoon> $ objdump -T /lib/libc-2.11.2.so | fgrep mremap - <teythoon> 00000000000cf7e0 w DF .text 0000000000000028 GLIBC_2.2.5 - mremap - <antrik> ah, it's probably simply a bug that we don't have this weak - reference too - <antrik> IIRC we had similar bugs before - <antrik> teythoon: can you provide a patch for that? - <teythoon> antrik: unfortunately I have no idea how that weak ref ended up - there +# IRC, freenode, #hurd, 2011-01-12 - <guillem> teythoon: also the libmemusage.s seems to be just a debugging - library to be used by LD_PRELOAD or similar - <guillem> which override those memory functions - <guillem> the libc should provide actual code for those functions, even if - the symbol is declared weak (so overridable) - <guillem> teythoon: are you sure that's the actual problem? can you paste - somewhere the build logs with the error? - <teythoon> guillem: sure - <teythoon> http://paste.debian.net/104437/ - <teythoon> that's the part of config.log that shows the detection (or the - failure to detect it) of mremap - <teythoon> this results in HAVE_MREMAP not being defined - <teythoon> as a consequence it is declared in gold.h and this declaration - conflicts with the one from sys/mman.h http://paste.debian.net/104438/ - <teythoon> on linux the test for mremap succeeds - <guillem> teythoon: hmm oh I guess it's just what that, mremap is linux - specific so it's not available on the hurd - <guillem> teythoon: I just checked glibc and seems to confirm that - <braunr> CONFORMING TO This call is Linux-specific, and should not be used - in programs intended to be portable. - <teythoon> ah okay - <teythoon> so I guess we shouldn't ship an header with that declaration... - <guillem> teythoon: yeah :/ good luck telling that to drepper :) - <guillem> teythoon: I guess he'll suggest that everyone else needs to get - our own copy of sys/mman.h - <guillem> s/our/their/ - <teythoon> hm, so how should I proceed? - <braunr> what's your goal ? - <braunr> detecting mremap ? - <teythoon> making binutils/gold compile ootb on hurd - <teythoon> I picked it from the open issues page ;) - <braunr> well, if there is no mremap, you need a replacement - <teythoon> gold has a replacement - <braunr> ok - <braunr> so your problem is fixing the detection of mremap right ? - <teythoon> yes - <braunr> ok, that's a build system question then :/ - <braunr> you need to ask an autotools guy - <teythoon> well, actually the build system correctly detects the absence of - mremap - <braunr> (gold does use the autotools right ?) - <teythoon> yes - <braunr> oh, i'm lost now (i admit i didn't read the whole issue :/) - <teythoon> it is just that the declaration in sys/mman.h conflicts with - their own declaration - <braunr> ah - <braunr> so in the absence of mremap, they use their own builtin function - <teythoon> yes - <teythoon> and according to the test suite it is working perfectly - <teythoon> gold that is - <teythoon> the declaration in mman.h has an extra __THROW - <guillem> a workaround would be to rename gold's mremap to something else, - gold_mremap for example - <braunr> that's really the kind of annoying issue - <braunr> you either have to change glibc, or gold - <guillem> yeah - <braunr> you'll face difficulty changing glibc, as guillem told you - <guillem> the correct solution though IMO is to fix glibc - <braunr> but this may be true for gold too - <braunr> guillem: i agree <antrik> maybe it would be easiest actually to implement mremap()?... - <braunr> but as this is something quite linux specific, it makes sense to - use another internal name, and wrap that to the linux mremap if it's - detected <braunr> antrik: i'm nto sure - <antrik> braunr: I don't think using such workarounds is a good - idea. clearly there would be no issue if the header file wouldn't be - incorrect on Hurd - <braunr> antrik: that's why i said i agree with guillem when he says "the - correct solution though IMO is to fix glibc" - <teythoon> what exactly is the problem with getting a patch into glibc? - <braunr> the people involved - <guillem> teythoon: and touching a generic header file - <braunr> but feel free to try, you could be lucky - <teythoon> but glibc is not an linux specific piece of software, right? - <braunr> teythoon: no, it's not - <guillem> erm... - <braunr> teythoon: but in practice, it is - <guillem> supposedly not :) - <antrik> braunr: BTW, by "easiest" I don't mean coding alone, but - coding+pushing upstream :-) - <guillem> so the problem is, misc/sys/mman.h should be a generic header and - as such not include linux specific parts, which are not present on hurd, - kfreebsd, etc etc - <braunr> antrik: yes, that's why guillem and i suggested the workaround - thing in gold - <antrik> that also requires pushing upstream. and quite frankly, if I were - the gold maintainer, I wouldn't accept it. - <guillem> but the easiest (and wrong) solution in glibc to avoid maintainer - conflict will probably be copying that file under hurd's glibc tree and - install that instead <braunr> antrik: implementing mremap could be relatively easy to do actually <braunr> antrik: IIRC, vm_map() supports overlapping - <antrik> well, actually the easiest solution would be to create a patch - that never goes upstream but is included in Debian, like many - others... but that's obviously not a good long-term plan <antrik> braunr: yes, I think so too <antrik> braunr: haven't checked, but I have a vague recollection that the fundamentals are pretty much there - <antrik> teythoon: so, apart from an ugly workaround in gold, there are - essentially three options: 1. implement mremap; 2. make parts of mman.h - conditional; 3. use our own copy of mman.h - <antrik> 1. would be ideal, but might be non-trivial; 2. would might be - tricky to get right, and even more tricky to get upstream; 3. would be - simple, but a maintenance burden in the long term - <teythoon> looking at golds replacement code (mmap & memcpy) 1 sounds like - the best option performance wise [[!taglink open_issue_glibc]]: check if it is possible to implement `mremap`. [[I|tschwinge]] remember some discussion about this, but have not yet worked on |