[llvm-dev] [RFC] [tools] Changing Behavior of LLVM binutils When No File Is Specified

Fāng-ruì Sòng via llvm-dev
Wed, 26 Jun 2019 05:40:48 -0000

GNU addr2line, nm, objdump, and size default to a.out when no input file is
specified.
Among llvm binary utilities, llvm-nm llvm-objdump llvm-size llvm-dwarfdump
default to a.out.

I agree with Michael that a.out behavior may not be used by many people. If
people don't care too much
about these utilities' compatibility with GNU, deleting the default a.out
LGTM.

(I am opposed to make more utilities default to a.out)

On Wed, Jun 26, 2019 at 9:02 AM Alex Brachet-Mialot via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> > Does anyone actually use the default to a.out behavior?
> This is a good point. What bugs me is continuity across the tools, I agree
> with you that it isn't particularly useful to default to a.out. But we
are
> kind of stuck with the weird way that GNU's binutils do things. I am
not in
> favor of llvm-objdump defaulting to a.out, but llvm-readelf giving this
> warning message. My guess is that moving away from using a.out by default
> for llvm-objdump, llvm-nm and others whose gnu counter parts do this would
> be more disruptive than my proposal.
>
> As Jake pointed out we use "-" to describe stdin/stdout,
GNU's tools do
> not do this, so I think there is some precedence for us slightly modifying
> behavior when we can reasonably say things will not happen, like the file
> "-" existing.
>
> On Tue, Jun 25, 2019 at 8:28 PM Michael Spencer <bigcheesegs at
gmail.com>
> wrote:
>
>> On Tue, Jun 25, 2019 at 4:58 PM Alex Brachet-Mialot via llvm-dev <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>> Some binutils, nm comes to mind, when to input file is specified
will
>>> default to a.out. Others do not do this and read from stdin by
default. The
>>> rest of this email will be specifically referencing these which
read from
>>> stdin, and not the tools which for various reasons do things
differently.
>>>
>>> I propose that we change the behavior of these tools to use a.out
when
>>> appropriate. By appropriate I mean firstly, no input file specified
and
>>> also no stream redirection to stdin. These are the file types of
stdin in
>>> these scenarios:
>>> $ writes-to-stdout | prog # named pipe (fifo)
>>> $ prog < file # regular file
>>> $ prog # reading from tty, character device
>>>
>>> Perhaps if stdin is a named pipe or regular file, then the default
>>> behavior should be as it always was, to read from stdin, but if
stdin is a
>>> tty then we should use a.out as a default file. This lets these
tools act
>>> the same as their gnu counterparts (when meaningful) but also adds
what I
>>> think is convenient to not have to specify a.out.
>>>
>>> This proposal would look something like this:
>>> $ llvm-strings # not meanigful to read from stdin here, look for
a.out
>>> $ llvm-strings < file # use stdin
>>>
>>> I may have got the behavior of stream redirection wrong here, or
missed
>>> a situation when reading from the terminal is useful. I would love
some
>>> feedback.
>>>
>>> Best,
>>> Alex
>>>
>>>
>> Does anyone actually use the default to a.out behavior?  I think it
would
>> be much friendlier to just print "file or pipe expected" and
then print the
>> help.
>>
>> - Michael Spencer
>>
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--
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