llvm dev - Nov 2013 - [LLVMdev] [lld] process undefined atoms from shared library only once

Hi Nick,

--start-group/--end-group functionality with the Gnu flavor currently 
works only if the --start-group/--end-group contains archive files.

If they contain dynamic libraries, the undefined atoms from the dynamic 
libraries are processed whenever the group is iterated again.

I am trying to find out a way to make the resolver add undefined atoms 
from the shared library only *once*, when the SharedLibrary is first 
visited as part of the Group.

The only approach that I can think of is having a std::map in the 
resolver and using that to process undefined atoms from shared libraries 
the first time the shared library is visited. I dont like this approach 
as its not clean.

Any alternative approaches to handle this ?

Thanks

Shankar Easwaran

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by the
Linux Foundation

I'd do that with the nextFile abstraction like this: On the first
iteration, a Group would return its member every time getNextFile() is
called (the same as the current behavior). On the second and further
iterations, the Group should skip all the members whose type is not
Archive. By doing this, the core linker sees dynamic libraries (or regular
object files) only once even if they are in --{start,end}-group.


On Mon, Nov 18, 2013 at 11:03 PM, Shankar Easwaran
<shankare at codeaurora.org>wrote:
> Hi Nick,
>
> --start-group/--end-group functionality with the Gnu flavor currently
> works only if the --start-group/--end-group contains archive files.
>
> If they contain dynamic libraries, the undefined atoms from the dynamic
> libraries are processed whenever the group is iterated again.
>
> I am trying to find out a way to make the resolver add undefined atoms
> from the shared library only *once*, when the SharedLibrary is first
> visited as part of the Group.
>
> The only approach that I can think of is having a std::map in the resolver
> and using that to process undefined atoms from shared libraries the first
> time the shared library is visited. I dont like this approach as its not
> clean.
>
> Any alternative approaches to handle this ?
>
> Thanks
>
> Shankar Easwaran
>
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted
> by the Linux Foundation
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20131119/ff8b41de/attachment.html>

Hi Rui,

I thought about this, but there is a catch. The undefined symbols still 
need to be resolved with exports from dynamic libraries even the second 
time, or any number of times.

For example :-

ld 1.o --start-group libc.so myprintf.a --end-group

1.o has a undef for myprintf, which is in myprintf.a and myprintf.a 
calls puts.

The first time when libc.so, undef atoms would be added, no shared 
library export atoms would be created because there is nothing that 
libc.so would resolve.

The second time, undefined symbols from shared libraries need to be 
skipped, and the external symbols that are present in the shared library 
libc.so need to be looked at.

To complicate things there is also --as-needed/--no-as-needed, where in 
a shared library is used only if its resolving symbols(the linker may 
need to handle undefined symbols/external symbols from shared library in 
any iteration).

Thanks

Shankar Easwaran


On 11/19/2013 1:49 PM, Rui Ueyama wrote:
> I'd do that with the nextFile abstraction like this: On the first
> iteration, a Group would return its member every time getNextFile() is
> called (the same as the current behavior). On the second and further
> iterations, the Group should skip all the members whose type is not
> Archive. By doing this, the core linker sees dynamic libraries (or regular
> object files) only once even if they are in --{start,end}-group.
>
>
> On Mon, Nov 18, 2013 at 11:03 PM, Shankar Easwaran
> <shankare at codeaurora.org>wrote:
>
>> Hi Nick,
>>
>> --start-group/--end-group functionality with the Gnu flavor currently
>> works only if the --start-group/--end-group contains archive files.
>>
>> If they contain dynamic libraries, the undefined atoms from the dynamic
>> libraries are processed whenever the group is iterated again.
>>
>> I am trying to find out a way to make the resolver add undefined atoms
>> from the shared library only *once*, when the SharedLibrary is first
>> visited as part of the Group.
>>
>> The only approach that I can think of is having a std::map in the
resolver
>> and using that to process undefined atoms from shared libraries the
first
>> time the shared library is visited. I dont like this approach as its
not
>> clean.
>>
>> Any alternative approaches to handle this ?
>>
>> Thanks
>>
>> Shankar Easwaran
>>
>> --
>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
hosted
>> by the Linux Foundation
>>
>>

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by the
Linux Foundation