[LLVMdev] Behaviour of outs()? (original) (raw)

Reid Kleckner rnk at google.com
Fri Jan 23 10:32:15 PST 2015

We've had this argument before. IMO LLVM should not be in the business of closing stdout, and no code in lib/ should print to stdout because users may expect output there (-o -).

On Fri, Jan 23, 2015 at 10:20 AM, Duncan P. N. Exon Smith < dexonsmith at apple.com> wrote:

> On 2015-Jan-23, at 09:52, mats petersson <mats at planetcatfish.com> wrote: > > I was just fixing a bug that was caused by stdout being closed > before the runtime has done fflush(stdout) [or however this is > implemented in the runtime]. > > The cause of this seems to be that outs() returns a static object > created from rawfdstream(STDOUTFILENO, true) - the true being > the shouldClose parameter. > > Surely LLVM is not supposed to close stdout as part of its operations? Looks like this was added in r111643: commit 5d56d9df928c48571980efe8d4205de8ab557b7c Author: Dan Gohman <gohman at apple.com> Date: Fri Aug 20 16:44:56 2010 +0000 Make outs() close its file when its stream is destructed, so that pending output errors are detected.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111643 91177308-0d34-0410-b5e6-96231b3b80d8 Certainly looks intentional. Comment in the code is: // Delete the file descriptor when the program exits, forcing error // detection. If you don't want this behavior, don't use outs(). I don't really have an opinion on whether this is a good idea, but it does suggest that any use of outs() in lib/ is a bug. $ git grep -l 'outs()' -- lib/ lib/ExecutionEngine/Interpreter/ExternalFunctions.cpp lib/IR/GCOV.cpp lib/Support/CommandLine.cpp lib/Support/FormattedStream.cpp lib/Support/TargetRegistry.cpp lib/Support/rawostream.cpp lib/Target/CppBackend/CPPBackend.cpp All of these cases seem to be for outputting help text of some sort. But probably they should be passed a reference to a rawostream, so that the caller gets to choose whether or not to use outs(). Were you hitting one of these?

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