On February 11, 2015 5:27:51 AM CST, Andrew Haley <[email protected]> wrote:
>On 02/11/2015 10:00 AM, Cyd Haselton wrote:
>>
>>
>> On February 11, 2015 2:36:59 AM CST, Andrew Haley <[email protected]>
>wrote:
>>> 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,
>>> when
>>>>> dlopen() was called the link would be correctly satisfied. If
>that
>>>>> 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
>in,
>>>> 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
>exported dlopen().
>
>But if it was linked in, where did the dlopen() link error come from?
>It
>should have succeeded because dlopen() should have been found in libdl.
>I still don't get it.
>
>Andrew.
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.
