llvm dev - Jun 2019 - [RFC] [tools] Changing Behavior of LLVM binutils When No File Is Specified

> 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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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
>>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>

-- 
宋方睿
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Sounds good, I'll work on removing these in favor of defaulting to stdin
then?
> I think it would be much friendlier to just print "file or pipe
expected"
and then print the help.
Do you have thoughts on this? I'm not sure there is a clean way to do this,
the cleanest would be through getFileOrSTDIN(), but I'm not sure all of its
users want this behavior. I don't think we need it personally, but if you
think its a good quality of life change to the tools and worth working on,
I'd be happy to do so.

On Wed, Jun 26, 2019 at 1:41 AM Fāng-ruì Sòng <maskray at google.com>
wrote:
> 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
>>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
>
> --
> 宋方睿
>
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