Date: Thu, 10 May 2012 08:56:59 -0400 From: Chet Ramey <chet.ramey@case.edu> To: Craig Rodrigues <rodrigc@crodrigues.org>, sbruno@freebsd.org Cc: Current FreeBSD <freebsd-current@freebsd.org>, chet.ramey@case.edu Subject: Re: ports/bash4 --enable-static fails Message-ID: <4FABBB1B.4080108@case.edu> In-Reply-To: <CAG=rPVdwu-k4bKNXBHuv47TL-90CrB_hV9ivzhD9E1LZhcRzig@mail.gmail.com> References: <1336599447.71431.2.camel@powernoodle-l7> <CAG=rPVdwu-k4bKNXBHuv47TL-90CrB_hV9ivzhD9E1LZhcRzig@mail.gmail.com>
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On 5/10/12 12:20 AM, Craig Rodrigues wrote: > Bash is trying to override the malloc() functions in libc with its own > implementation in lib/malloc/malloc.c . > I have seen this type of trick before 3rd party code that tries to > override the libc implementation of malloc() / free() with its own. > > kan@ explained this to me before, but I don't know if I can explain it > as well as him, because it has to do > with how static linking works. :) > > Basically, the malloc.o object from bash, *must* have implementations of > *all* the relevant functions in jemalloc_jemalloc.o in order for > malloc.o to properly override jemalloc_jemalloc.o. > > If you have something like: > jemalloc_jemalloc.o (libc) malloc.o (Bash) > =============== ============= > malloc() malloc() > free() free() > calloc() > realloc() > > > the static linker will not be able to replace jemalloc_jemalloc.o from > libc with malloc.o from Bash, > because calloc() and realloc() symbols in jemalloc_jemalloc.o (libc) > do not exist malloc.o (Bash). > > Since the linker can only deal with whole objects (.o files), it will > try to pull in both > jemalloc_jemalloc.o and malloc.o when doing static linking. > > I may have got some of the details/explanation wrong, but I have fixed > something similar > to this in 3rd party code, when the layout of malloc() functions in > libc changed between FreeBSD 4 and FreeBSD 6. This explanation is substantially correct. > > What you need to do is: > (1) run nm or readelf on jemalloc_jemalloc.o, then run nm or > readelf on malloc.o > (2) Look at the symbols in both > (3) Add the missing symbols to malloc.c in Bash The bash malloc includes definitions for malloc/free/realloc/calloc/cfree/ valloc/memalign. I'd be interested in knowing what other global symbols jemalloc exports. I'd also be interested in seeing how someone managed to compile the bash malloc and leave out realloc. Chet -- ``The lyf so short, the craft so long to lerne.'' - Chaucer ``Ars longa, vita brevis'' - Hippocrates Chet Ramey, ITS, CWRU chet@case.edu http://cnswww.cns.cwru.edu/~chet/
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