diff options
| -rw-r--r-- | open_issues/binutils_gold.mdwn | 176 |
1 files changed, 175 insertions, 1 deletions
diff --git a/open_issues/binutils_gold.mdwn b/open_issues/binutils_gold.mdwn index f9008154..aa6843a3 100644 --- a/open_issues/binutils_gold.mdwn +++ b/open_issues/binutils_gold.mdwn @@ -1,4 +1,4 @@ -[[!meta copyright="Copyright © 2010 Free Software Foundation, Inc."]] +[[!meta copyright="Copyright © 2010, 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 @@ -11,3 +11,177 @@ License|/fdl]]."]]"""]] [[!tag open_issue_binutils]] Have a look at GOLD / port as needed. + + +# teythoon's try / `mremap` issue + +IRC, #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... + +[[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 + + <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 +locating it. [[Talk to me|tschwinge]] if you'd like to have a look at this. |