#5019: OS X: ld: warning: could not create compact unwind for _ffi_call_unix64
-------------------------------+--------------------------------------------
Reporter: altaic | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.1 | Keywords:
Testcase: | Blockedby:
Os: MacOS X | Blocking:
Architecture: x86_64 (amd64) | Failure: Incorrect warning at compile-time
-------------------------------+--------------------------------------------
The OS X 10.6 linker now defaults to creating compact unwinds, which is a
good thing, however the unwind info for `_ffi_call_unix64` can't be
represented in the compact format. This warning is issued any time ghc
links, and many tests in the test suite fail due to the extra output:
{{{
ld: warning: could not create compact unwind for _ffi_call_unix64: does
not use RBP or RSP based frame
}}}
Possible solutions:
* suppress the warning in ld; unfortunately this does not seem to be
possible, since the only applicable option is `-warn_compact_unwind` which
enables the already enabled-by-default warnings
* suppress the warning in ghc; I haven't really looked into this, but one
could filter the text output from the linker to remove the warning
* entirely disable compact unwinds using `-no_compact_unwind`; this flag
is undocumented, so I'm not certain about what it really does
* patch `_ffi_call_unix64` in libffi to make it compatible with compact
unwinds
Info about compact unwinds in OS X 10.6 is somewhat scarce, but `man
unwinddump` has a bit:
{{{
When a C++ (or x86_64 Objective-C) exception is thrown, the runtime must
unwind the
stack looking for some function to catch the exception. Traditionally,
the unwind
information is stored in the __TEXT/__eh_frame section of each executable
as Dwarf
CFI (call frame information). Beginning in Mac OS X 10.6, the unwind
information is
also encoded in the __TEXT/__unwind_info section using a two-level lookup
table of
compact unwind encodings.
The unwinddump tool displays the content of the __TEXT/__unwind_info
section.
}}}
Relevant discussions:
[http://groups.google.com/group/llvm-
dev/browse_thread/thread/8baba4531a9feb07/139c9eba3525ebe]
[http://groups.google.com/group/darwin-
dev/browse_thread/thread/962f74bde0efaae4/cfb63dfb3ac34ce1]
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5019>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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