[LLVMdev] raw_ostream behavior

[Dan Gohman]

Standard error is what many tools, including clang for example, use for
their --verbose output. This is appropriate because it leaves standard
output available for regular output data, which the user may wish to
capture in a file or a pipe.

Dan


On Wed, Aug 14, 2013 at 2:48 PM, Shankar Easwaran
<shankare at codeaurora.org>wrote:

> Hi Dan,
>
> The other messages, need to go to stdout as well. Using stderr to output
> for a switch like --verbose is wrong in my opinion.
>
>
> On 8/14/2013 4:44 PM, Dan Gohman wrote:
>
>> Would it be appropriate for lld's other output to go to standard error
>> instead of standard output, since standard output may be used for YAML
>> output?
>>
>> Dan
>>
>> On Wed, Aug 14, 2013 at 12:53 PM, Shankar Easwaran
>> <shankare at codeaurora.org>**wrote:
>>
>>  Hi Dan,
>>>
>>> lld takes a -emit-yaml option, which emits the intermediate
>>> representation(atoms) in YAML form.
>>>
>>> By default output goes to stdout, the user can control it by using the -o
>>> option too.
>>>
>>> The way its handled is, similiar to this piece of pseudo-code
>>>
>>> if (dash_o_option)
>>>      outputFile = dash_o_option->value()
>>> else
>>>     outputFile = "-"
>>>
>>> When lld tries to mix things that go to stdout using llvm::outs() and
>>> -emit-yaml, it starts to get this error.
>>>
>>> If there is a restriction like this, possibly it has to be mentioned
>>> somewhere for usecases (or) raw_fd_ostream should not be accepting a '-'
>>> in
>>> the argument.
>>>
>>> What do you think ?
>>>
>>> Thanks
>>>
>>> Shankar Easwaran
>>>
>>>
>>> On 8/14/2013 2:02 PM, Dan Gohman wrote:
>>>
>>>  The high-level answer is that library code shouldn't hardcode output
>>>> paths,
>>>> including "-" and including using llvm::outs(). Library code should (in
>>>> general) instead accept an ostream in its API and write to wherever it
>>>> is
>>>> being asked to write. If this is followed, the only place in any program
>>>> using llvm::outs() is code which is not part of a "library" -- i.e. it
>>>> is
>>>> the "main" code, and it should only do so if it is a program which
>>>> doesn't
>>>> open file names which could be "-".
>>>>
>>>> Do you have a use-case where this restriction is too restrictive?
>>>>
>>>> As a random aside, a more aggressive answer could be that "-" is a kind
>>>> of
>>>> hack, and that it would be a better approach to use /dev/stdout and
>>>> /dev/stdin instead of "-", because they wouldn't require special-case
>>>> logic. Unfortunately, this may not be sufficiently portable.
>>>>
>>>> Dan
>>>>
>>>>
>>>> On Wed, Aug 14, 2013 at 8:28 AM, Shankar Easwaran
>>>> <shankare at codeaurora.org>****wrote:
>>>>
>>>>   Hi,
>>>>
>>>>> When I run the below example, it results in :-
>>>>>
>>>>> hello
>>>>> world
>>>>> LLVM ERROR: IO failure on output stream.
>>>>>
>>>>> Testcase :-
>>>>>
>>>>> #include <llvm/Support/raw_ostream.h>
>>>>>
>>>>> int fn() {
>>>>>     std::string errorInfo;
>>>>>     llvm::raw_fd_ostream out("-", errorInfo);
>>>>>     out << "world\n";
>>>>>     return 0;
>>>>> }
>>>>> int main(int argc, char **argv) {
>>>>>     llvm::outs() << "hello\n";
>>>>>     fn();
>>>>>     return 0;
>>>>> }
>>>>>
>>>>> I tried to fix this by making llvm::outs(), not close the stdout
>>>>> descriptor, but I think its wrong. Recommendations ?
>>>>>
>>>>> Thanks
>>>>>
>>>>> Shankar Easwaran
>>>>>
>>>>> --
>>>>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
>>>>> hosted
>>>>> by the Linux Foundation
>>>>>
>>>>>
>>>>>
>>>>> ______________________________******_________________
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>>>>>
>>>>>  --
>>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted
>>> by the Linux Foundation
>>>
>>>
>>>
>
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted
> by the Linux Foundation
>
>
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