id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
2730	Quasiquote or TH linking may need HPC flag	simonpj		"Test `quasiquotation/qq005` fails in the `hpc` way:
{{{
'/64playpen/simonpj/builds/HEAD-1/ghc/stage2-inplace/ghc' -fforce-recomp -dcore-lint -dcmm-lint -Dx86_64_unknown_linux  -dno-debug-output -c -o qq005 Main.hs -O -fhpc
Loading package ghc-prim ... linking ... done.
Loading package integer ... linking ... done.
Loading package base ... linking ... done.
Loading package ffi-1.0 ... linking ... done.
Loading package syb ... linking ... done.
Loading package array-0.2.0.0 ... linking ... done.
Loading package packedstring-0.1.0.1 ... linking ... done.
Loading package containers-0.2.0.0 ... linking ... done.
Loading package pretty-1.0.1.0 ... linking ... done.
Loading package template-haskell ... linking ... done.
Loading package parsec-2.1.0.1 ... linking ... done.
ghc: ./Expr.o: unknown symbol `hs_hpc_module'
}}}
I believe the reason is this:
 * `Expr.hs` contains a quasiquote parser
 * This parser is invoked in `Main.hs`
 * But `Expr.hs` is compiled with `-fhpc` and contains a reference to the RTS function `hs_hpc_module`
 * When doing dynamic linking of `Expr.o` (to run the quasiquote parser) the linker can't find `hs_hpc_module`.  (Even though `Main.hs` is also compiled with `-fhpc`.

The same thing happens with Template Haskell. (Try running the `th` tests with the `hpc` way.  Not all tests fail, but some do, with the same error.)

I'm no expert on the dynamic linking part. Is `hs_hpc_module` (defined in `rts/Hpc.c`) always part of the RTS?  Does it need to be added to a list I vaguely recall, of externally linkable symbols (perhaps `RTS_SYMBOLS` in `rts/Linker.c`) [PS: some comments explaining these lists would be v useful]?  Or what?

I'll milestone this for 6.10.1, because it does seem a bug that TH and HPC don't mix; but it should probably not hold up the release.

Simon"	bug	closed	normal	6.10.2	Compiler	6.10.1	duplicate			Unknown/Multiple	Unknown/Multiple		Unknown