#3625: GHCI doesn't work with dtrace on OS X
--------------------+-------------------------------------------------------
Reporter: rl | Owner:
Type: bug | Status: new
Priority: normal | Component: GHCi
Version: 6.10.4 | Severity: normal
Keywords: | Testcase:
Os: MacOS X | Architecture: Unknown/Multiple
--------------------+-------------------------------------------------------
On OS X, user-defined dtrace probes are implemented as special symbols of
the form `___dtrace_probe$...` which are magically resolved by the linker.
In the attached package, we have this dtrace script:
{{{
provider haskell {
probe demo__trace(char*);
};
}}}
and this C file:
{{{
void demo_trace( char *s )
{
HASKELL_DEMO_TRACE(s);
}
}}}
When we compile it, we get:
{{{
newbie:dtrace-demo rl$ nm demo-trace.o
U ___dtrace_probe$haskell$demo__trace$v1$63686172202a
U ___dtrace_stability$haskell$v1$1_1_0_1_1_0_1_1_0_1_1_0_1_1_0
U ___dtrace_typedefs$haskell$v1
00000000 T _demo_trace
}}}
When linked as a dynamic library, the undefined symbols disappear:
{{{
newbie:dtrace-demo rl$ ld -dylib -o demo-trace.dylib demo-trace.o
newbie:dtrace-demo rl$ nm demo-trace.dylib
00000000 t __mh_dylib_header
000008b0 T _demo_trace
}}}
But GHCI's linker can't resolve the symbols which means that GHCI will
fail if it tries to load demo-trace.o or a package file that contains
demo-trace.o. For the attached package, `ghci -package dtrace-demo`
produces this error:
{{{
unknown symbol `___dtrace_probe$haskell$demo__trace$v1$63686172202a'
Loading package dtrace-demo-1.0 ... linking ... ghc: unable to load
package `dtrace-demo-1.0'
}}}
Unless I'm mistaken, the only solution is to use dlopen instead of a hand-
written linker as the dtrace symbols are actually resolved by the kernel.
The problem came up while implementing dtrace-based profiling for DPH. DPH
uses Template Haskell so GHC tries to load a package which uses dtrace and
dies.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3625>
GHC <http://www.haskell.org/ghc/>
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