Resolving a Haskell `stack build --profile` g++ Linker Error

Question

Context: I am using stack to profile a build which uses FFI invocations to C++ code (via inline-C, a template haskell extension).

Problem: When running stack build, the project builds fine. But when running stack build --profile, however, I get the following g++ linker error:

$ stack build --profile

Sling-0.1.0.0: configure
Configuring Sling-0.1.0.0...
Sling-0.1.0.0: build
Preprocessing executable 'Sling-exe' for Sling-0.1.0.0...
[1 of 4] Compiling SimpleCompositor ( src/SimpleCompositor.hs, .stack-work/dist/x86_64-linux-ncurses6/Cabal-1.24.0.0/build/Sling-exe/Sling-exe-tmp/SimpleCompositor.p_o )
[2 of 4] Compiling Struct           ( src/Struct.hs, .stack-work/dist/x86_64-linux-ncurses6/Cabal-1.24.0.0/build/Sling-exe/Sling-exe-tmp/Struct.p_o )
[3 of 4] Compiling Lib              ( src/Lib.hs, .stack-work/dist/x86_64-linux-ncurses6/Cabal-1.24.0.0/build/Sling-exe/Sling-exe-tmp/Lib.p_o )
[4 of 4] Compiling Main             ( main/Main.hs, .stack-work/dist/x86_64-linux-ncurses6/Cabal-1.24.0.0/build/Sling-exe/Sling-exe-tmp/Main.p_o )
Linking .stack-work/dist/x86_64-linux-ncurses6/Cabal-1.24.0.0/build/Sling-exe/Sling-exe ...
.stack-work/dist/x86_64-linux-ncurses6/Cabal-1.24.0.0/build/Sling-exe/Sling-exe-tmp/SimpleCompositor.p_o: In function `c99J_info':
/tmp/ghc22572_0/ghc_9.p_o:(.text+0x77e): undefined reference to `inline_c_SimpleCompositor_5_c5df445469e64aa7738f9848cfc9b677b917df47'
.stack-work/dist/x86_64-linux-ncurses6/Cabal-1.24.0.0/build/Sling-exe/Sling-exe-tmp/SimpleCompositor.p_o: In function `r90H_info':
/tmp/ghc22572_0/ghc_9.p_o:(.text+0x8e2): undefined reference to `inline_c_SimpleCompositor_4_4128a18e34f611cc08850d5bf36de9ac2707d1b2'
.stack-work/dist/x86_64-linux-ncurses6/Cabal-1.24.0.0/build/Sling-exe/Sling-exe-tmp/SimpleCompositor.p_o: In function `r90I_info':
/tmp/ghc22572_0/ghc_9.p_o:(.text+0xae2): undefined reference to `inline_c_SimpleCompositor_3_d0fe1ab601f5030423845b84b10160e1cbd9d79a'
.stack-work/dist/x86_64-linux-ncurses6/Cabal-1.24.0.0/build/Sling-exe/Sling-exe-tmp/SimpleCompositor.p_o: In function `r90J_info':
/tmp/ghc22572_0/ghc_9.p_o:(.text+0xdc2): undefined reference to `inline_c_SimpleCompositor_2_c9e46c413b75c4c01bb29f4321b9275f056c0911'
.stack-work/dist/x86_64-linux-ncurses6/Cabal-1.24.0.0/build/Sling-exe/Sling-exe-tmp/SimpleCompositor.p_o: In function `r90K_info':
/tmp/ghc22572_0/ghc_9.p_o:(.text+0xfc2): undefined reference to `inline_c_SimpleCompositor_1_fff40540e3a02ca3c27ae8f1c780462c1cbb82d0'
.stack-work/dist/x86_64-linux-ncurses6/Cabal-1.24.0.0/build/Sling-exe/Sling-exe-tmp/SimpleCompositor.p_o: In function `r90L_info':
/tmp/ghc22572_0/ghc_9.p_o:(.text+0x11c2): undefined reference to `inline_c_SimpleCompositor_0_2e4a0d3a8c4b9baa2fc6947c1d65b62df44e96df'
.stack-work/dist/x86_64-linux-ncurses6/Cabal-1.24.0.0/build/Sling-exe/Sling-exe-tmp/SimpleCompositor.p_o: In function `s91O_info':
/tmp/ghc22572_0/ghc_9.p_o:(.text+0x1438): undefined reference to `inline_c_SimpleCompositor_2_c9e46c413b75c4c01bb29f4321b9275f056c0911'
.stack-work/dist/x86_64-linux-ncurses6/Cabal-1.24.0.0/build/Sling-exe/Sling-exe-tmp/SimpleCompositor.p_o: In function `s91W_info':
/tmp/ghc22572_0/ghc_9.p_o:(.text+0x18f0): undefined reference to `inline_c_SimpleCompositor_4_4128a18e34f611cc08850d5bf36de9ac2707d1b2'
.stack-work/dist/x86_64-linux-ncurses6/Cabal-1.24.0.0/build/Sling-exe/Sling-exe-tmp/SimpleCompositor.p_o: In function `s925_info':
/tmp/ghc22572_0/ghc_9.p_o:(.text+0x1c62): undefined reference to `inline_c_SimpleCompositor_5_c5df445469e64aa7738f9848cfc9b677b917df47'
.stack-work/dist/x86_64-linux-ncurses6/Cabal-1.24.0.0/build/Sling-exe/Sling-exe-tmp/SimpleCompositor.p_o: In function `s92u_info':
/tmp/ghc22572_0/ghc_9.p_o:(.text+0x2363): undefined reference to `inline_c_SimpleCompositor_0_2e4a0d3a8c4b9baa2fc6947c1d65b62df44e96df'
/tmp/ghc22572_0/ghc_9.p_o:(.text+0x2534): undefined reference to `inline_c_SimpleCompositor_1_fff40540e3a02ca3c27ae8f1c780462c1cbb82d0'
collect2: error: ld returned 1 exit status
`g++' failed in phase `Linker'. (Exit code: 1)

--  While building package Sling-0.1.0.0 using:
      /home/user/.stack/setup-exe-cache/x86_64-linux-ncurses6/setup-Simple-Cabal-1.24.0.0-ghc-8.0.1 --builddir=.stack-work/dist/x86_64-linux-ncurses6/Cabal-1.24.0.0 build exe:Sling-exe --ghc-options " -ddump-hi -ddump-to-file"
    Process exited with code: ExitFailure 1

Weirdly enough: If I delete .stack-work from my project and then run the following sequence:

$ stack build
$ stack build --profile

The profiling works!

Why is this? Relying on this hack to get profiling working can't be good.

Answer 1

It looks that there are references being generated by Template Haskell that are not available when doing the profile.

As answered in this question, c-inline is differentiated from inline-c by the fact that it always generates the same identifiers basing the naming on the function contents.

That's why you could get those linker errors:

• First, you build your project and it generates all the necessary references made with TH.
• Second, when rebuilding the project with stack build --profile, incremental compilation is triggered and the identifiers are not created again, but the calls do, resulting in a linker error.

When you delete your .stack-work folder you force stack to rebuild the whole project and generate the identifiers correctly.

A solution could be relying on a Makefile that cleans the project cache by removing .stack-work.