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Re: Android native build of GCC
- From: Cyd Haselton <chaselton at gmail dot com>
- To: Andrew Haley <aph at redhat dot com>
- Cc: Hans-Peter Nilsson <hp at bitrange dot com>,"gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>
- Date: Fri, 13 Feb 2015 16:40:42 -0600
- Subject: Re: Android native build of GCC
- Authentication-results: sourceware.org; auth=none
- References: <54AE581C dot 5070003 at redhat dot com> <alpine dot BSF dot 2 dot 02 dot 1502060258210 dot 10842 at arjuna dot pair dot com> <54D48673 dot 9070901 at redhat dot com> <alpine dot BSF dot 2 dot 02 dot 1502060458370 dot 29537 at arjuna dot pair dot com> <54D49731 dot 7030407 at redhat dot com> <F47323AC-2C7B-47B8-B630-D03A629DD347 at gmail dot com> <54D4A6C2 dot 1040808 at redhat dot com> <CAHu5Prbo2J1p2ueC3G5A6r-ZUo0z6JG1X_9OmshEyKPjjh0hTQ at mail dot gmail dot com> <54D4EA79 dot 10909 at redhat dot com> <6A2D97AB-19B8-4A78-ABE7-B486D1C41FCC at gmail dot com> <54DB14AB dot 3040501 at redhat dot com> <87A6FCF6-9A36-43DE-9981-6663EF51D81F at gmail dot com> <54DB3CB7 dot 1040108 at redhat dot com>
On February 11, 2015 5:27:51 AM CST, Andrew Haley <email@example.com> wrote:
>On 02/11/2015 10:00 AM, Cyd Haselton wrote:
>> On February 11, 2015 2:36:59 AM CST, Andrew Haley <firstname.lastname@example.org>
>>> On 11/02/15 00:41, Cyd Haselton wrote:
>>>>> I'd rather leave it on-list for future reference. The best thing
>>>>> would be for libfakechroot to be linked against libdl: that way,
>>>>> dlopen() was called the link would be correctly satisfied. If
>>>>> isn't possible (if dlopen() doesn't work or is incompatible) then
>>>>> libfakechroot shouldn't export the symbol for dlopen().
>>>> After experimenting with several builds of the fakechroot library I
>>>> can't see how this would be possible. Even when libdl is linked
>>>> hiding dlopen guarantees that the resulting library doesn't
>>>> intercept dlopen calls, which breaks the fakechroot environment and
>>>> removing the fakechroot dlopen code also ensures that dlopen calls
>>>> aren't intercepted.
>>> I don't get it. If libdl is linked in, why would you hide dlopen()
>> libdl was linked in the original, buggy libfakechroot...the one that
>But if it was linked in, where did the dlopen() link error come from?
>should have succeeded because dlopen() should have been found in libdl.
>I still don't get it.
After a few days of looking at the code and running readelf on various builds of libfakechroot, I don't either...but I have a guess.
The libfakechroot wraps a number of libc commands up in a way that exports a global function named after the libc funct and a local object with the name fakechroot_libcfunction_wrapper. Example:
bld/fakechrt/fakechroot-2.16 $ readelf -a src/.libs/libfakechroot.so | grep getcwd 94: 000050fc 232 FUNC GLOBAL DEFAULT 7 getcwd
53: 00000000 0 FILE LOCAL DEFAULT ABS __getcwd_chk.c
238: 00000000 0 FILE LOCAL DEFAULT ABS getcwd.c
553: 000102e8 12 OBJECT LOCAL DEFAULT 14 fakechroot_getcwd_wrapper
672: 000050fc 232 FUNC GLOBAL DEFAULT 7 getcwd
Somehow these calls are passed to libc by the wrapper including the dlopen() call...which fails because it should be passed to libdl on android.
How the wrapper points to libc I have no idea. Why the wrapper around dlopen doesn't pick up 0n the linked libdl.so...again, I have no idea. Someone with better knowledge of fakechroot internals, symbols and linking will have to tackle this.
Sent from my Android device with K-9 Mail. Please excuse my brevity.