Re: [PATCH] gdb, configure: Add disable-formats option for configure

[Guinevere Larsen <guinevere@redhat.com>]

On 10/8/24 8:44 AM, Eli Zaretskii wrote:
>> Date: Mon, 7 Oct 2024 16:58:16 -0300
>> Cc: aburgess@redhat.com, gdb-patches@sourceware.org
>> From: Guinevere Larsen <guinevere@redhat.com>
>>
>> On 10/7/24 4:17 PM, Eli Zaretskii wrote:
>>> That's a good starting point, but IMO it stops short of answering the
>>> practical questions people will ask themselves.  For example, how do I
>>> configure GDB to support a single target that is my native target and
>>> OS? will specifying the single format from the above list do?
>> If a user wants to configure their native target, that is related to the
>> --target and --enable-target options. Not the file formats. This change
>> is not related to how a user decides to support any given CPU or
>> operating system, but rather, which binary files they wish GDB to be
>> able to understand. If the user knows they want Windows and Linux, but
>> don't know how to specify that, they should look at documentation for
>> --target and --enable-targets, which is not touched by this patch or
>> related to this change whatsoever.
> I think there's a misunderstanding.  I said "to support a single
> target", meaning _only_ that single target.
>
> You seem to be saying that --target is what I want, but that's not
> what I knew.  Right now, when I compile GDB for native Windows
> debugging, I get all the *read.c files compiled and linked into GDB.
> I don't specify --target when I build GDB, but I do specify --build,
> and I thought that --build=FOO is a short for --host=FOO --target=FOO.
> So I thought that I am already specifying --target, and yet I get all
> the binary-format readers compiled and linked in.  So I was asking
> what should I do at configure time to have only the *read.c files I
> need for that single target and only for native debugging.
Then I guess the response you wanted is the paragraph you omitted in 
this response:

     Once they know what target they are running, it will most likely be 
Linux, Windows or MacOS, which are called out by name in this 
description. If it is something different, the user is likely savvy 
enough to look up online what their operating system supports, as there 
are no users of these platforms who do so because it's the default in 
the mainstream machine they bought.

If you know that your platform is FOO, you can either easily find it in 
the list, or it is a specialized system that you chose to use, and are 
likely to know better than me where to find that information.

>
> If you are saying that the --enable-binary-format is unrelated to my
> questions, then I guess I'm even more confused than I thought I was.
>
>>> One thing I remember is that many targets produce core files in ELF
>>> format.  If that is true, then omitting ELF should be discouraged for
>>> that reason.  And maybe also other similar practical factoids.
>>>
>> I believe that is the case because there are many targets that use ELF
>> as the objfile format.
> True, but not what I was saying: I was specifically alluding to
> targets whose objfile format is _not_ ELF, and yet they produce core
> files in ELF format.  ISTR that Cygwin is one such target?  I'm sure
> others here will be able to find more examples.

Which is all the more reason for GDB to not be the owner of this type of 
documentation.

I couldn't find any information about how core files were handled in 
Windows, but as soon as you - someone who clearly knows the system - 
brought up that maybe elf should be used with cygwin, a quick search for 
the specification found a footnote confirming this.

We should not be expected to keep on top of all the specifications of 
all targets we own so we can suggest to possible users that maybe they 
want this if they use some specific configuration.

Ultimately, this is a feature for advanced users who have deep domain 
knowledge on the systems they expect to handle, and similar to how, even 
with the update on the --target and --enable-targets documentation, I 
wouldn't expect every single target triplet supported by GDB to be 
listed in the documentation, I don't think we should list what formats 
are recommended for each target.

I can change the first paragraph of the description to read as follows:
   Configure GDB to only be be able to read selected file formats. The
   special value "all" causes all file formats to be compiled in, and is 
the
   the default behavior of the option. If you are unsure of which options
   you will need for your debugging sessions, we recommend that you
   not make use of this function. The possible options are:

<list of options as sent in previous email>

>
>> And once again, users don't need to interact with this feature. If it is
>> completely ignored, GDB will continue to work just as it did before this
>> patch went in.
> I understand, and that is good, but I'm talking from the POV of
> someone who _wants_ to use this new feature, in order to make GDB
> smaller.
>
> Thanks.
>

-- 
Cheers,
Guinevere Larsen
She/Her/Hers