[LLVMdev] raw_ostream behavior

[Dan Gohman]

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
>>>
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>>>
>
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