From: tad.bochan@...
Date: 2004-08-31T19:22:30+09:00
Subject: Réf. : Dereferencing pointers returned by syscall



Hi Florian,

Thanks very much for your tip. It does intrigue me how you came to know
about
this one (ruby/DL).

Unfortunately, I haven't been able to verify that it works yet  because of
an apparent
bug in ruby when I try the syscall to mmap. I  running 1.8.0 on HPUX, and I
can't
upgrade to a later version just yet. (don't have an ansi C compiler!)

""""
> cat pntrs.rb
#require "dl"
#Foo=Struct.new("Foo",:astrg)
SYS_mmap          = 71
PROT_NONE         = 0
PROT_USER         = 0
PROT_READ         = 1
PROT_WRITE        = 2
MAP_SHARED        = 1
addr,len,prot,flags,ofs=0,80,PROT_READ, MAP_SHARED,0
filedes=open("shmfile","r+")
mmfptr=syscall(SYS_mmap, addr, len, prot, flags, filedes.fileno, ofs)

Gives ...........................
> ruby pntrs.rb
pntrs.rb:11: [BUG] rb_sys_fail() - errno == 0
ruby 1.8.0 (2003-08-04) [hppa2.0w-hpux11.11]

Abort(coredump)
>
""""

But a rather odd problem occurs when I run the above with the 'require'
line uncommented,

> cat pntrs.rb
require "dl"
#Foo=Struct.new("Foo",:astrg)
SYS_mmap          = 71
PROT_NONE         = 0
PROT_USER         = 0
PROT_READ         = 1
PROT_WRITE        = 2
MAP_SHARED        = 1
addr,len,prot,flags,ofs=0,80,PROT_READ, MAP_SHARED,0
filedes=open("shmfile","r+")
mmfptr=syscall(SYS_mmap, addr, len, prot, flags, filedes.fileno, ofs)

Gives ...........................

> ruby pntrs.rb
pntrs.rb:11:in `syscall': No such file or directory (Errno::ENOENT)
        from pntrs.rb:11
>




Internet
flgr@ccan.de - 26/08/2004 21:05


Veuillez r�pondre � ruby-talk@ruby-lang.org

Pour : ruby-talk

cc :


Objet :     Re: Dereferencing pointers returned by syscall


tad.bochan@bnpparibas.com wrote:

> Hi,

Moin!

> I'm using 'syscall' in ruby to access the 'mmap'  function in Unix
(HPUX),
> to try to read/write a memory-mapped file.
> The 'mmap' function returns a pointer to the mapped file.
> I can't figure out how I am supposed to be able to use
> this pointer  to access the data from ruby.

Have a look at Ruby/DL which is part of Standard Ruby. With
DL::Importable you can create a struct like this:

Foo = struct [
   "long foo",
   "int bar",
   ...
]

And later you can do Foo.new(DL::PtrData.new(ptr)).

Regards,
Florian Gross










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