[LLVMdev] raw_ostream behavior

[Nick Kledzik]

Shankar,

What is the other output going to stdout?  Seems like it could get mixed into the yaml output, causing problems.

If -o is not supplied, the linker normally writes to a file called “a.out”.    If this is for the core linker when running test suites, may would should have the core linker create a temp file or string buffer to write to (if -o not supplied) and then at the end read from that file and write to stdout.

-Nick

On 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
>>>>> 
>>>>> --
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>>>>> by the Linux Foundation
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>>>>> 
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>>> 
>>> 
> 
> 
> -- 
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by the Linux Foundation