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IDProjectCategoryView StatusDate SubmittedLast Update
0006700OCamldocumentationpublic2014-12-09 20:152017-03-15 13:56
Assigned To 
Platformamd64OSOS Version
Product Version 
Target VersionFixed in Version 
Summary0006700: ocamlopt -shared -o creates by-products in a confusing place; documentation clarification welcome
DescriptionWhen I run ocamlopt -shared and use -o to arrange to that the output file is not
in the same directory as the source file, I see that by-products (*.o and *.cmi)
are stored along the source file.

It is expected that these by products are stored in the same directory as the file given as argument to the -o option. Indeed,

1. This is the behaviour of the compiler when producing a cmi as a a by-product
   of a cmo file.

2. The sources can sit on a read-only media and the user guarantees that the
   path used with the -o file is writeable.

3. Makefiles using the objdir-system¹ to store object files in a directory
   distinct from the sources are easier to use if no object file is created
   in the source directory.

¹: esp BSD Owl ( [^])
Steps To Reproducemkdir remote
touch remote/
ocamlopt -shared -o module.cmxs remote/
ls -R
Attached Files

- Relationships

-  Notes
gasche (developer)
2014-12-14 00:26

This behavior is actually consistent with the way other compilation command work, such as when you ask to produce a bytecode executable from a source file (or several source files) directly:

  ocamlc -o foo remote/

will first compile into a module.cmo (choosing to produce the compiled files in remote/), and then link the produced .cmo into a bytecode executable. Notice the difference with the two-step process

  ocamlc -o module.cmo -c remote/
  ocamlc -o foo module.cmo

which produces everything in the current module -- and has the ability to say so explicitly. In the same way you can produce your .cmxs as follows:

  ocamlopt -o module.cmx -c remote/
  ocamlopt -shared -o module.cmxs module.cmx

and no byproduct will be stored in remote/.

I'm worried by the idea of changing the default behavior in this use-case (the risk of breaking other build scripts seems important). Could you not use the more precise two-step process instead?
michipili (reporter)
2014-12-15 11:27

Thank you for your feedback. Using the more precise two-step procedure is of course feasible and there is no need to change ocaml behaviour.

Looking at the official documentation¹, I could not deduce properly how to prepare dynlink native plugins. Maybe I overlooked something, maybe the description of the -shared flag could be enhanced by using a stance similar to the one used for the -a flag:

> Build a library (.cmxa and .a/.lib files) with the object files (.cmx and .o/.obj files) given on the command line, instead of linking them into an executable file. The name of the library must be set with the -o option.

In its current phrasing, the description of the -shared flag misses two important features present in the snippet above:

- explictly listing .cmx files as valid input
- the [Build… instead of linking them into an executable.]

In my opinion, using a similar wording to describe the -shared and -a flags would clarify the manual. But this is just my opinion! :)

¹ [^]
gasche (developer)
2014-12-15 15:16

That seems sensible. If you or anyone is motivated to provide a better-worded patch, I'm ready to merge it. [^]

- Issue History
Date Modified Username Field Change
2014-12-09 20:15 michipili New Issue
2014-12-14 00:26 gasche Note Added: 0012804
2014-12-14 00:26 gasche Status new => feedback
2014-12-15 11:27 michipili Note Added: 0012820
2014-12-15 11:27 michipili Status feedback => new
2014-12-15 15:16 gasche Note Added: 0012827
2014-12-15 15:16 gasche Tag Attached: junior_job
2014-12-15 15:17 gasche Severity minor => text
2014-12-15 15:17 gasche Status new => acknowledged
2014-12-15 15:17 gasche Category OCaml general => OCaml documentation
2014-12-15 15:17 gasche OS FreeBSD =>
2014-12-15 15:17 gasche OS Version 10.1 =>
2014-12-15 15:17 gasche Product Version 4.02.1 =>
2014-12-15 15:17 gasche Summary ocamlopt -shared -o creates by-products in the wrong directory => ocamlopt -shared -o creates by-products in a confusing place; documentation clarification welcome
2015-01-13 23:03 doligez Severity text => minor
2015-01-13 23:03 doligez Target Version => 4.03.0+dev / +beta1
2016-04-18 15:03 doligez Target Version 4.03.0+dev / +beta1 => 4.03.1+dev
2017-02-16 14:01 doligez Target Version 4.03.1+dev => undecided
2017-02-23 16:35 doligez Category OCaml documentation => Documentation
2017-02-23 16:44 doligez Category Documentation => documentation
2017-03-15 13:56 doligez Target Version undecided =>

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