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|ID||Project||Category||View Status||Date Submitted||Last Update|
|0004795||OCaml||OCaml general||public||2009-05-19 13:46||2011-05-29 12:19|
|Target Version||Fixed in Version||3.12.0+dev|
|Summary||0004795: -fPIC error with x86_64|
|Description||ocamlc and ocamlopt fail to compile to dynamic libraries on linux x86_64.|
Reproducible as follows:
$ echo "let x = 5" > lib.ml
$ ocamlc -output-obj -o lib.so lib.ml
/usr/bin/ld: /usr/lib/ocaml/libcamlrun.a(stacks.o): relocation R_X86_64_32 against `a local symbol' can not be used when making a shared object; recompile with -fPIC
/usr/lib/ocaml/libcamlrun.a: could not read symbols: Bad value
collect2: ld returned 1 exit status
File "lib.ml", line 1, characters 0-1:
Error: Error while building custom runtime system
|Tags||No tags attached.|
|Attached Files|| amd64-pic.S [^] (13,976 bytes) 2010-02-16 23:43|
amd64-pic.v2.S [^] (14,321 bytes) 2010-02-17 21:54
edited on: 2009-07-11 07:18
The bug still exists even if compile libasmrun with -fPIC flag set:
$ ./configure -cc "gcc -fPIC" -aspp "gcc -fPIC -c"
$ /home/xram/ocaml/bin/ocamlopt -output-obj -o lib.so lib.ml
/usr/bin/ld: /home/xram/ocaml/lib/ocaml/libasmrun.a(amd64.o): relocation R_X86_64_PC32 against `caml_last_return_address' can not be used when making a shared object; recompile with -fPIC
It seems like asmrun/amd64.S doesn't produce position-independent code.
|I have uploaded amd64-pic.S which is a drop-in replacement for amd64.S. The new assembly file creates position independent code if you define the macro EMIT_PIC=1. With EMIT_PIC=0 it behaves exactly like the stock amd64.S that comes with ocaml-3.11.1. So there is no need for Xavier to worry about performance. Only if you actually need PIC you take the performance hit.|
Thanks for the replacement amd64.S. Much appreciated.
You're definitely on the right track, but I noticed a potential
problem in the caml_call_gc and caml_alloc* functions: the code
generator assumes they preserve all registers except %rax, but you're
using %r11 as a scratch register... For caml_call_gc, it should be
possible to move the series of "pushq" ahead of the STORE_VARs. For
caml_alloc*, some more footwork is needed to free a scratch register.
If you have ideas, please do let me know; otherwise, I'll try to
finish this before the 3.12.0 release.
I addressed the %r11 issue in the amd64-pic.v2.S that I just attached to this issue.
I tried this new amd64.S (EMIT_PIC=1) by regressing through some 120,000 lines of ocaml code that I have here, and regression passes. Actually, it also passed yesterday when register %r11 was still clobbered on some occasions, I guess I was lucky then ...
Thanks for the second version of the patch. I merged it in the development sources, to be released as 3.12.0. I made a tiny simplification in caml_allocN, and also used "#if __PIC__" instead of "#if EMIT_PIC", so that assembling with "gcc -c -fPIC" selects the PIC version. Let me know if you see a problem with that.
I still cannot succeed to link code generated by ocamlopt in a shared library under Linux x86_64.
I'm using the amd64.S from the trunk (after looking at 0004795) and take care to compile everything with -fPIC. I get this error:
/usr/bin/ld: /home/afrisch/branches/v4/mlfi/mlfi-ins/lib/libasmrun.a(amd64.o): relocation R_X86_64_PC32 against symbol `caml_alloc1' can not be used when making a shared object; recompile with -fPIC
Any help will be appreciated!
To my surprise, the assembler does not resolve a "jmp" to a global symbol defined in the same file, leaving an absolute reference to the symbol instead of putting a relative displacement :-( One learns something new every day. I just commited a fix to asmrun/amd64.S. The relocs look good and gcc -shared no longer complains.
|2009-05-19 13:46||paolo||New Issue|
|2009-05-20 14:10||doligez||Status||new => assigned|
|2009-05-20 14:10||doligez||Assigned To||=> xleroy|
|2009-07-11 07:17||zinid||Note Added: 0005018|
|2009-07-11 07:18||zinid||Note Edited: 0005018|
|2010-02-16 23:43||paul_stravers||File Added: amd64-pic.S|
|2010-02-16 23:48||paul_stravers||Note Added: 0005244|
|2010-02-17 17:46||xleroy||Note Added: 0005247|
|2010-02-17 21:54||paul_stravers||File Added: amd64-pic.v2.S|
|2010-02-17 22:04||paul_stravers||Note Added: 0005248|
|2010-03-29 14:18||xleroy||Note Added: 0005275|
|2010-03-29 14:18||xleroy||Status||assigned => resolved|
|2010-03-29 14:18||xleroy||Resolution||open => fixed|
|2010-03-29 14:18||xleroy||Fixed in Version||=> 3.12.0+dev|
|2010-04-15 15:15||frisch||Note Added: 0005313|
|2010-04-15 15:15||frisch||Status||resolved => feedback|
|2010-04-15 15:15||frisch||Resolution||fixed => reopened|
|2010-04-19 10:49||xleroy||Note Added: 0005341|
|2010-04-19 10:49||xleroy||Status||feedback => resolved|
|2010-04-19 10:49||xleroy||Resolution||reopened => fixed|
|2011-05-29 12:19||xleroy||Status||resolved => closed|
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