Agner`s CPU blog

Software optimization resources | E-mail subscription to this blog | www.agner.org

Rethinking DLLs and shared objects
Author:  Date: 2016-05-30 08:06

I like the idea of getting rid of the indirection on every call to a library function; that seems like a good plan. Current software is of course designed for the current situation of lazy dynamic linking. This non-lazy dynamic linking may not do very well with some existing software.

GUIs tend to use a lot of library code. I'm worried that copying so much code into private memory for every process will use significant amounts of memory. It won't be touched a lot of the time, but everything that's reachable from the QT or GTK API functions used by a program has to be read from disk and copied into the process's private memory, not just mmap(MAP_SHARED). This means it can only be paged out to swap space, since the library text isn't backed by a file on disk.

Web browsers build much of their code as libraries. Many browsers use multiple processes instead of just multiple threads, as an extra barrier against vulnerabilities. On Linux, I assume chrome just fork()s, so memory that isn't modified after that is shared. AFAIK, Windows doesn't have an equivalent system call, so each process might be stuck with its own private copy of all the library code.

In summary, I think the current state of desktop software is too bloated for this to be a good idea.

If we hope to ever see any of this proposal get used for real (at some point in the far future?), I think we might need some kind of lazy dynamic linking, or at least shared text segments for libraries. Vendors will always want to be able to sell cheap machines with the minimum amount of memory.

Non-lazy linking sounds great for long-running processes that don't overdo it with libraries (e.g. a web server process), but I'm also worried about higher startup overhead for commands used from shell-scripts. With lazy dynamic linking, code for functions that are never called (because that command-line option wasn't used) doesn't ever have to be read into memory. OTOH, most programs will use the same libc functions, and having them hot in the pagecache means it's cheap for the dynamic linker to memcpy them.

It would be interesting to run some tests comparing shell-script speed (cut/grep/sed/cat/find) with Linux lazy dynamic linking vs. this proposal. I think this could work on x86, or any other arch. Linux supports custom executable file formats, or for this experiment we could use ELF with a different dynamic linker as a custom ELF-interpreter. IDK if we'd want a different library object-file format, though, to make it easy and fast to recursively find all the functions a library-function could itself call.

 
thread Proposal for an ideal extensible instruction set new - Agner - 2015-12-27
replythread Itanium new - Ethan - 2015-12-28
last reply Itanium new - Agner - 2015-12-28
replythread Proposal for an ideal extensible instruction set new - hagbardCeline - 2015-12-28
last replythread Proposal for an ideal extensible instruction set new - Agner - 2015-12-28
reply Proposal for an ideal extensible instruction set new - Adrian Bocaniciu - 2016-01-04
reply Proposal for an ideal extensible instruction set new - Adrian Bocaniciu - 2016-01-04
reply Proposal for an ideal extensible instruction set new - Adrian Bocaniciu - 2016-01-04
replythread Proposal for an ideal extensible instruction set new - Adrian Bocaniciu - 2016-01-04
reply Proposal for an ideal extensible instruction set new - Adrian Bocaniciu - 2016-01-05
replythread Proposal for an ideal extensible instruction set new - John D. McCalpin - 2016-01-05
last reply Proposal for an ideal extensible instruction set new - Adrian Bocaniciu - 2016-01-06
last reply Proposal for an ideal extensible instruction set new - Ook - 2016-01-05
last reply Proposal for an ideal extensible instruction set new - acppcoder - 2016-03-27
reply Proposal for an ideal extensible instruction set new - Jake Stine - 2016-01-11
replythread Proposal for an ideal extensible instruction set new - Agner - 2016-01-12
last replythread Proposal for an ideal extensible instruction set new - Jonathan Morton - 2016-02-02
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-02-03
last replythread Proposal for an ideal extensible instruction set new - Jonathan Morton - 2016-02-12
last replythread Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-02-18
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-02-21
last replythread Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-02-22
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-02-23
replythread Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-02-23
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-02-24
last replythread Proposal for an ideal extensible instruction set new - asdf - 2016-02-24
last reply Proposal for an ideal extensible instruction set new - Agner - 2016-02-24
last reply Proposal for an ideal extensible instruction set new - Agner - 2016-02-25
replythread limit instruction length to power of 2 new - A-11 - 2016-02-24
last replythread limit instruction length to power of 2 new - Agner - 2016-02-24
replythread Any techniques for more than 2 loads per cycle? new - Hubert Lamontagne - 2016-02-24
last reply Any techniques for more than 2 loads per cycle? new - Agner - 2016-02-25
last replythread limit instruction length to power of 2 new - A-11 - 2016-02-25
last reply limit instruction length to power of 2 new - Hubert Lamontagne - 2016-02-25
replythread More ideas new - Agner - 2016-03-04
replythread More ideas new - Hubert Lamontagne - 2016-03-07
last reply More ideas new - Agner - 2016-03-08
last reply More ideas new - Agner - 2016-03-09
replythread Proposal for an ideal extensible instruction set new - Joe Duarte - 2016-03-07
reply Proposal for an ideal extensible instruction set new - Agner - 2016-03-08
last replythread Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-03-08
last replythread Proposal for an ideal extensible instruction set new - Joe Duarte - 2016-03-09
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-03-10
last replythread Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-03-11
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-03-11
last replythread Proposal for an ideal extensible instruction set new - anon2718 - 2016-03-13
last reply Proposal for an ideal extensible instruction set new - Agner - 2016-03-14
replythread A design without a TLB new - Agner - 2016-03-11
replythread A design without a TLB new - Hubert Lamontagne - 2016-03-11
reply A design without a TLB new - Agner - 2016-03-11
last reply A design without a TLB new - Agner - 2016-03-12
reply A design without a TLB new - Bigos - 2016-03-13
last reply A design without a TLB new - Agner - 2016-03-28
replythread Proposal now published new - Agner - 2016-03-22
last replythread Proposal now published new - Hubert Lamontagne - 2016-03-23
last replythread Proposal now published new - Agner - 2016-03-24
last replythread Proposal now published new - Hubert Lamontagne - 2016-03-24
last replythread Proposal now published new - Agner - 2016-03-24
last replythread Proposal now published new - Hubert Lamontagne - 2016-03-24
last replythread Proposal now published new - Agner - 2016-03-25
last replythread Proposal now published new - Hubert Lamontagne - 2016-03-28
last replythread Proposal now published new - Agner - 2016-03-29
last replythread Proposal now published new - Hubert Lamontagne - 2016-03-30
last replythread Proposal now published new - Agner - 2016-03-30
last replythread Do we need instructions with two outputs? new - Agner - 2016-03-31
last replythread Do we need instructions with two outputs? new - Hubert Lamontagne - 2016-04-01
reply Do we need instructions with two outputs? new - Agner - 2016-04-01
replythread Do we need instructions with two outputs? new - Joe Duarte - 2016-04-02
last replythread Do we need instructions with two outputs? new - Agner - 2016-04-02
last reply Do we need instructions with two outputs? new - Joe Duarte - 2016-04-02
last replythread Do we need instructions with two outputs? new - Agner - 2016-04-02
last replythread Do we need instructions with two outputs? new - Hubert Lamontagne - 2016-04-02
last replythread Do we need instructions with two outputs? new - Agner - 2016-04-03
reply Do we need instructions with two outputs? new - Joe Duarte - 2016-04-03
last replythread Do we need instructions with two outputs? new - Hubert Lamontagne - 2016-04-03
last replythread Do we need instructions with two outputs? new - Agner - 2016-04-04
reply Do we need instructions with two outputs? new - Hubert Lamontagne - 2016-04-04
last replythread Do we need instructions with two outputs? new - Joe Duarte - 2016-04-06
last replythread Do we need instructions with two outputs? new - Hubert Lamontagne - 2016-04-07
last replythread Do we need instructions with two outputs? new - HarryDev - 2016-04-08
last reply Do we need instructions with two outputs? new - Hubert Lamontagne - 2016-04-09
replythread How about stack machine ISA? new - A-11 - 2016-04-10
last replythread treating stack ISA as CISC architecure new - A-11 - 2016-04-14
last replythread treating stack ISA as CISC architecure new - Agner - 2016-04-14
last replythread treating stack ISA as CISC architecure new - A-11 - 2016-04-17
replythread treating stack ISA as CISC architecure new - Hubert Lamontagne - 2016-04-17
last replythread stack ISA versus long vectors new - Agner - 2016-04-18
last replythread stack ISA versus long vectors new - Hubert Lamontagne - 2016-04-19
last reply stack ISA versus long vectors new - Agner - 2016-04-20
last reply treating stack ISA as CISC architecure new - A-11 - 2016-04-18
replythread Proposal for an ideal extensible instruction set new - zboson - 2016-04-11
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-04-11
last replythread Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-04-11
last replythread Proposal for an ideal extensible instruction set new - Agner - 2016-04-12
last reply Proposal for an ideal extensible instruction set new - Hubert Lamontagne - 2016-04-12
replythread Version 1.01 new - Agner - 2016-05-10
last replythread Version 1.01 new - Hubert Lamontagne - 2016-05-13
last replythread Version 1.01 new - Agner - 2016-05-14
last replythread Version 1.01 new - Harry - 2016-06-02
replythread Public repository new - Agner - 2016-06-02
reply Public repository new - Harry - 2016-06-02
last reply Public repository new - Harry - 2016-06-02
last reply Public repository new - Agner - 2016-06-09
replythread Rethinking DLLs and shared objects new - Agner - 2016-05-20
replythread Rethinking DLLs and shared objects new - cv - 2016-05-20
last reply Rethinking DLLs and shared objects new - Agner - 2016-05-20
replythread Rethinking DLLs and shared objects - Peter Cordes - 2016-05-30
last replythread Rethinking DLLs and shared objects new - Agner - 2016-05-30
last replythread Rethinking DLLs and shared objects new - Joe Duarte - 2016-06-17
last replythread Rethinking DLLs and shared objects new - Agner - 2016-06-18
last reply Rethinking DLLs and shared objects new - Bigos - 2016-06-18
last replythread Rethinking DLLs and shared objects new - Freddie Witherden - 2016-06-02
last replythread Rethinking DLLs and shared objects new - Agner - 2016-06-04
last replythread Rethinking DLLs and shared objects new - Freddie Witherden - 2016-06-04
last reply Rethinking DLLs and shared objects new - Agner - 2016-06-06
replythread Is it better to have two stacks? new - Agner - 2016-06-05
reply Is it better to have two stacks? new - Hubert Lamontagne - 2016-06-07
replythread Is it better to have two stacks? new - Eden Segal - 2016-06-13
last replythread Is it better to have two stacks? new - Agner - 2016-06-13
last replythread Is it better to have two stacks? new - Hubert Lamontagne - 2016-06-14
last replythread Is it better to have two stacks? new - Agner - 2016-06-14
last replythread Is it better to have two stacks? new - Hubert Lamontagne - 2016-06-15
last replythread Is it better to have two stacks? new - Agner - 2016-06-15
last replythread Is it better to have two stacks? new - Hubert Lamontagne - 2016-06-16
last replythread Is it better to have two stacks? new - Agner - 2016-06-16
last reply Is it better to have two stacks? new - Hubert Lamontagne - 2016-06-17
last reply Is it better to have two stacks? new - Freddie Witherden - 2016-06-22
last reply Now on Github new - Agner - 2016-06-26