[Bug libc/12234] New: iconvlist API

[Bug libc/12234] New: iconvlist API

[tromey at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12234

           Summary: iconvlist API
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: libc
        AssignedTo: drepper.fsp@gmail.com
        ReportedBy: tromey@redhat.com


Currently gdb has to invoke "iconv -l" and parse its output
in order to determine the list of available charsets.
It would be nice if glibc provided an iconvlist API, like libiconv,
to avoid this.

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[Bug libc/12234] iconvlist API

[jan.kratochvil at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12234

Jan Kratochvil <jan.kratochvil at redhat dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |jan.kratochvil at redhat
                   |                            |dot com

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[Bug libc/12234] iconvlist API

[drepper.fsp at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12234

Ulrich Drepper <drepper.fsp at gmail dot com> changed:

           What    |Removed                     |Added
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             Status|NEW                         |WAITING

--- Comment #1 from Ulrich Drepper <drepper.fsp at gmail dot com> 2010-11-18 22:21:34 UTC ---
You don't say why you think you need that.

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[Bug libc/12234] iconvlist API

[tromey at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12234

--- Comment #2 from Tom Tromey <tromey at redhat dot com> 2010-11-19 19:18:55 UTC ---
gdb lets the user indicate the target charset.
In order to allow command-line completion we need a list of charsets.

Having an API is nicer than trying to parse iconv -l output.
Right now we have to have workarounds for old/strange versions of iconv.
Also this means that every gdb startup involves a second fork/exec.

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[Bug libc/12234] iconvlist API

[drepper.fsp at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12234

--- Comment #3 from Ulrich Drepper <drepper.fsp at gmail dot com> 2010-11-19 21:50:06 UTC ---
You shouldn't offer this.  Having a name on the list doesn't guarantee that a
conversion between any two of the listed encodings is possible.  The only way
to find out whether it is possible is by calling iconv_open.

Even if you overlook this flaw in your use, such an interface doesn't belong
into libc.  Except for your use there is no known user.

The only possibility I'd except is to make the iconv program a PIE.  Then you
could dlopen() the file and call a special function.  That function could
return in some way or form the list of encodings.  This wouldn't require any
code duplication.  But is it really worth the time?  The forking really
shouldn't be that expensive.

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[Bug libc/12234] iconvlist API

[jan.kratochvil at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12234

--- Comment #4 from Jan Kratochvil <jan.kratochvil at redhat dot com> 2010-12-07 08:20:15 UTC ---
(In reply to comment #3)
> such an interface doesn't belong into libc.
> Except for your use there is no known user.

This is a chicken-and-egg problem.  How there can be a user of nonexisting API?


> The only possibility I'd except is to make the iconv program a PIE.  Then you
> could dlopen() the file and call a special function.

This idea contradicts "How To Write Shared Libraries", section 1.6.
  Number of Objects: The fact that a smaller number of objects containing
  the same functionality is beneficial has been mentioned in several places
  [...]


> But is it really worth the time?  The forking really shouldn't be that
> expensive.

Isn't the prelink optimizing an even cheaper operation - dynamic relocating?

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[Bug libc/12234] iconvlist API

[drepper.fsp at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12234

--- Comment #5 from Ulrich Drepper <drepper.fsp at gmail dot com> 2010-12-07 14:26:03 UTC ---
(In reply to comment #4)
> This is a chicken-and-egg problem.  How there can be a user of nonexisting API?

People could have tried to do exactly what you do today.  Nobody does.  This is
why I say there are no other users.


> This idea contradicts "How To Write Shared Libraries", section 1.6.
>   Number of Objects: The fact that a smaller number of objects containing
>   the same functionality is beneficial has been mentioned in several places
>   [...]

You seem to miss how the PIE solution would work.  The iconv program would
continue to work as before.  It'd just be loaded slightly differently.  But at
the same time you could use the same file in dlopen() and then get a pointer to
a function which returns the list.


> > But is it really worth the time?  The forking really shouldn't be that
> > expensive.
> 
> Isn't the prelink optimizing an even cheaper operation - dynamic relocating?

I don't quite follow.  Of course will any specialized solution to get the list
be faster than forking.  I was asking why this is a bottleneck for you in the
first place.  This is something which has to be done in response to a user
action.  The command line interaction of the user should be much slower than
any fork and reading the result.

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[Bug libc/12234] iconvlist API

[jan.kratochvil at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12234

--- Comment #6 from Jan Kratochvil <jan.kratochvil at redhat dot com> 2010-12-07 16:48:14 UTC ---
(In reply to comment #5)
> (In reply to comment #4)
> > This idea contradicts "How To Write Shared Libraries", section 1.6.
> 
> You seem to miss how the PIE solution would work.  The iconv program would
> continue to work as before.  It'd just be loaded slightly differently.  But at
> the same time you could use the same file in dlopen() and then get a pointer to
> a function which returns the list.

GDB will have to load two shared libraries (glibc+iconv) instead of just one
(glibc).  This is against the "How To Write Shared Libraries" recommendation.


> I was asking why this is a bottleneck for you in the
> first place.  This is something which has to be done in response to a user
> action.  The command line interaction of the user should be much slower than
> any fork and reading the result.

GDB is also being called from various scripts.  GDB currently does not allow to
make the iconv list initialization lazy due to its existing commands
infrastructure.  Thanks for the advice how to optimize it on the GDB side.

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[Bug libc/12234] iconvlist API

[jan.kratochvil at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=12234

Jan Kratochvil <jan.kratochvil at redhat dot com> changed:

           What    |Removed                     |Added
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             Status|WAITING                     |NEW

--- Comment #7 from Jan Kratochvil <jan.kratochvil at redhat dot com> 2011-05-11 08:36:37 UTC ---
There had to be --with-iconv-bin introduced now as the applications depending
on iconv need to use both its functions and finds its iconv binary:
http://sourceware.org/ml/gdb-patches/2011-05/msg00169.html

There is no more info to provide about this RFE, clearing WAITING.

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[Bug libc/12234] iconvlist API

[schwab@linux-m68k.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=12234

Andreas Schwab <schwab@linux-m68k.org> changed:

           What    |Removed                     |Added
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         AssignedTo|drepper.fsp at gmail dot    |unassigned at sourceware
                   |com                         |dot org

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[Bug libc/12234] iconvlist API

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=12234

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
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              Flags|                            |security-

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[Bug locale/12234] iconvlist API

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=12234

Joseph Myers <jsm28 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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          Component|libc                        |locale

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