dynamic-link on libc

dynamic-link on libc

[Jeff Mickey]

Hi guilers!

I cannot seem to call `dynamic-link' on libc.

I'm trying to write a simple, dumb wrapper around syslog using the 
(system foreign) dynamic library to learn how to use the dynamic 
ffi.

(use-modules (system foreign))
 
(define libcsyslog (dynamic-link "libc"))  (define syslog 
  (let ((f (pointer->procedure 
	    void (dynamic-func "syslog" libcsyslog) (list int 
	    '*)))) 
    (lambda (level msg) 
      (let* ((clevel level) 
	     (cmsg (string->pointer msg))) (f clevel cmsg))))) 
	(syslog 3 "hello there") 


This works when I symlink /lib/x86_64-linux-gnu/libc.so.6 to 
libc.so, but it looks like the libtool library that is doing the 
load doesn't accept names that end in ".6" as a library name, and 
when I used the full path it just says "file not found".

Anyone have suggestions? I looked at the dynl.c sysdep_dynl_link 
function, but I'm not sure I understand libtool well enough to 
know what lt_dlopenext should be doing.

I should add I tested this on a debian system with a debian 
provided guile, and a "user installed guix" guile install as well.

Thanks!

  //  codemac

Re: dynamic-link on libc

[Matt Wette]

> On Aug 4, 2017, at 2:15 PM, Jeff Mickey <j@codemac.net> wrote:
> 
> Hi guilers!
> 
> I cannot seem to call `dynamic-link' on libc.
> 
> I'm trying to write a simple, dumb wrapper around syslog using the (system foreign) dynamic library to learn how to use the dynamic ffi.
> 
> (use-modules (system foreign))
> (define libcsyslog (dynamic-link "libc"))  (define syslog  (let ((f (pointer->procedure 	    void (dynamic-func "syslog" libcsyslog) (list int 	    '*))))    (lambda (level msg)      (let* ((clevel level) 	     (cmsg (string->pointer msg))) (f clevel cmsg))))) 	(syslog 3 "hello there") 
> 
> This works when I symlink /lib/x86_64-linux-gnu/libc.so.6 to libc.so, but it looks like the libtool library that is doing the load doesn't accept names that end in ".6" as a library name, and when I used the full path it just says "file not found".
> 
> Anyone have suggestions? I looked at the dynl.c sysdep_dynl_link function, but I'm not sure I understand libtool well enough to know what lt_dlopenext should be doing.
> 
> I should add I tested this on a debian system with a debian provided guile, and a "user installed guix" guile install as well.
> 
> Thanks!
> 
> //  codemac
> 

I don’t think you need to dynamic-link libc; just use (dynamic-func "syslog" (dynamic-link)).

Re: dynamic-link on libc

[Jeff Mickey]

That solves my problem! Thank you so much :)

libc is a special case, and I should have thought about it more.

  //  mickey

On Fri, Aug 4, 2017, at 14:44, Matt Wette wrote:
> 
> > On Aug 4, 2017, at 2:15 PM, Jeff Mickey <j@codemac.net> wrote:
> > 
> > Hi guilers!
> > 
> > I cannot seem to call `dynamic-link' on libc.
> > 
> > I'm trying to write a simple, dumb wrapper around syslog using the (system foreign) dynamic library to learn how to use the dynamic ffi.
> > 
> > (use-modules (system foreign))
> > (define libcsyslog (dynamic-link "libc"))  (define syslog  (let ((f (pointer->procedure 	    void (dynamic-func "syslog" libcsyslog) (list int 	    '*))))    (lambda (level msg)      (let* ((clevel level) 	     (cmsg (string->pointer msg))) (f clevel cmsg))))) 	(syslog 3 "hello there") 
> > 
> > This works when I symlink /lib/x86_64-linux-gnu/libc.so.6 to libc.so, but it looks like the libtool library that is doing the load doesn't accept names that end in ".6" as a library name, and when I used the full path it just says "file not found".
> > 
> > Anyone have suggestions? I looked at the dynl.c sysdep_dynl_link function, but I'm not sure I understand libtool well enough to know what lt_dlopenext should be doing.
> > 
> > I should add I tested this on a debian system with a debian provided guile, and a "user installed guix" guile install as well.
> > 
> > Thanks!
> > 
> > //  codemac
> > 
> 
> I don’t think you need to dynamic-link libc; just use (dynamic-func
> "syslog" (dynamic-link)).
>