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

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
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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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> 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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