0005693: Missing '_environ' symbol used in libunix.a

Notes
(0007787) xleroy (administrator) 2012-07-20 18:58	Which version of XCode are you using? As I said on caml-list, the "environ" variable is standard according to POSIX and Single Unix Specification, so something went terribly wrong here. Damien, Xavier C.: can you reproduce on your Macs?

(0007788) xleroy (administrator) 2012-07-20 20:10 edited on: 2012-07-20 20:10	More info posted by reporter on caml-list: My setting is: Mac OS X 10.7.4 gcc version: i686-apple-darwin11-llvm-gcc-4.2 ocaml 3.12.1 Xcode 4.3.3 (4E3002) I don't develop in Xcode, but use makefiles instead. Homebrew was used to install ocaml. The error only occurs when linking to a dynamic lib, not when I link against an executable (main loop in c).

(0007789) thelema (reporter) 2012-07-20 23:01	Per Benedikt Meurer on caml-list: Of course... as stated in environ(7): "Shared libraries and bundles don't have direct access to environ, which is only available to the loader ld(1) when a complete program is being linked. The environment routines can still be used, but if direct access to environ is needed, the _NSGetEnviron() routine, defined in <crt_externs.h>, can be used to retrieve the address of environ at run- time." It has always been this way on OS X, so Keyan's patch is correct.

(0007792) doligez (manager) 2012-07-21 21:26	That command line looks suspect to me: 1. "-o libocaml_rl_pi_rnn.so": this tells ocamlopt to name its output file libocaml_rl_pi_rnn.so, but there is nothing to tell it that you want to build a shared library, so ocamlopt is going to make an executable and name it libocaml_rl_pi_rnn.so. This is probably not what you want. Note that you never get "undefined symbol" errors when building shared libraries. 2. "-ccopt -shared": from gcc's man page: -shared Produce a shared object which can then be linked with other objects to form an executable. Not all systems support this option. For predictable results, you must also specify the same set of options that were used to generate code (-fpic, -fPIC, or model suboptions) when you specify this option.[1] This option is not supported on Mac OS X. In any case, I cannot reproduce the bug as reported. When I do "ocamlopt -o foo.so unix.cmxa -ccopt -shared", I get errors, not only on _environ, but also on _caml_atom_table, _caml_code_area_start, and _caml_code_area_end. I have uploaded an example that's almost working, but when I run a.out I get this error: dlopen(./foo.so, 2): Symbol not found: _caml_atom_table Referenced from: /Users/doligez/dynlink-example/foo.so Expected in: flat namespace in /Users/doligez/dynlink-example/foo.so Xavier, can you tell us what's I'm missing?

(0007797) doligez (manager) 2012-07-23 16:20	OK, what I was missing is the surprising semantics of COMMON data in C object files and its variations across C linkers... We'll probably have a better fix in a future version of OCaml, but for now you need to reference a function from "startup.c", to prevent the Mac OS X linker from dropping the file when building your shared library. See the new version of my example code (I've also fixed bar.c to avoid a segfault).

(0007798) doligez (manager) 2012-07-23 16:33 edited on: 2012-07-24 09:38	Note for the future: the best solution we found so far is to add an initializer to every global variable of the runtime system, to force them into the data segment. An other possibility: make the OCaml compiler output references to caml_atom_table as common rather than imported symbol.

(0007826) doligez (manager) 2012-07-27 13:19	I have uploaded a more complete example that demonstrates passing arguments, returning values, and catching exceptions (dynlink-example3).

Issue History
Date Modified	Username	Field	Change
2012-07-20 18:45	thelema	New Issue
2012-07-20 18:58	xleroy	Note Added: 0007787
2012-07-20 18:58	xleroy	Status	new => feedback
2012-07-20 20:10	xleroy	Note Added: 0007788
2012-07-20 20:10	xleroy	Note Edited: 0007788	View Revisions
2012-07-20 23:01	thelema	Note Added: 0007789
2012-07-20 23:01	thelema	Status	feedback => new
2012-07-21 21:25	doligez	File Added: dynlink-example.tgz
2012-07-21 21:26	doligez	Note Added: 0007792
2012-07-21 21:26	doligez	Status	new => feedback
2012-07-23 16:20	doligez	Note Added: 0007797
2012-07-23 16:21	doligez	File Added: dynlink-example-new.tgz
2012-07-23 16:29	doligez	File Deleted: dynlink-example-new.tgz
2012-07-23 16:29	doligez	File Added: dynlink-example2.tgz
2012-07-23 16:33	doligez	Note Added: 0007798
2012-07-23 16:33	doligez	Status	feedback => confirmed
2012-07-23 16:33	doligez	Target Version	=> 4.01.0+dev
2012-07-24 09:38	doligez	Note Edited: 0007798	View Revisions
2012-07-27 13:18	doligez	File Added: dynlink-example3.tar.gz
2012-07-27 13:19	doligez	Note Added: 0007826
2012-07-31 13:36	doligez	Target Version	4.01.0+dev => 4.00.1+dev
2012-09-21 14:51	doligez	Priority	normal => low
2012-09-21 14:51	doligez	Target Version	4.00.1+dev => 4.01.0+dev

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