Fixing dlopen("libpthread.so")

[Daniel Eischen]

On Wed, 7 Jan 2015, Konstantin Belousov wrote:

> On Tue, Jan 06, 2015 at 09:50:46PM +0100, Jilles Tjoelker wrote:
>> On Mon, Jan 05, 2015 at 04:37:08AM +0200, Konstantin Belousov wrote:
>>> Next natural question is about the __error calls through PLT in the
>>> .cerror asm. Before the work was committed, libthr interposed __error,
>>> which was required for correct operation. Now, we need __error exported,
>>> but do we need support its interposing ? This is an implementation
>>> detail for errno, I do not see any loss from not allowing to override
>>> errno location.
>>
>> Indeed, there is no need to allow interposing __error (as with many
>> libc-internal calls to its exported symbols). Additionally, the current
>> namespace.h mechanism could be used to redirect __error calls from C
>> code.
>>
>> Glibc uses macro trickery with the asm labels compiler feature, making
>> libc code see things like
>>   int *__error(void) asm("__hidden__error");
>> and defining the hidden alias somewhere. This also works for
>> compiler-generated calls like to memcpy(). I'm not sure whether it is a
>> good idea to add this extra trickery and depend on the compiler feature.
> I might look at this after the current change is committed.

I don't quite follow all the above about __error(), but non-C
programs need to interface to an __error() that works regardless
of threading or not.

--
DE