[LLVMdev] raw_ostream behavior

[Shankar Easwaran]

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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