Choice of linker should consider whether it supports LDFLAGS

[hseg]

Describe the bug
network, time, unix fail to build when LDFLAGS contains -Wl,-z,pack-relative-relocs. This is because cabal builds them with LD=ld.gold, which doesn't support this feature. This breaks builds on Arch Linux, whose default build configuration recently added the flag to LDFLAGS.

To Reproduce
Steps to reproduce the behavior:

export LDFLAGS='-Wl,-z,pack-relative-relocs'
git clone https://github.com/haskell/network
cabal configure
cabal build

Expected behavior

cabal build tests $LD $LDFLAGS works before picking it, and then either warns ld.gold doesn't support LDFLAGS as set or Could not find working linker

System information

• Operating system: Arch Linux
• cabal, ghc versions: cabal-install 3.10.2.1, ghc 9.8.2

Additional context
Reported in Arch Linux upstream as well, and in GHC which had a similar issue. Also mistakenly reported this in stack due to initial confusion as to the cause.

[andreabedini]

Is cabal calling the linker here or GHC?

@erikd You looked at linker feature detection before. Do you have any take on this?

[hseg]

Frustratingly, am having difficulty reproducing, though I updated both ghc and cabal recently, so that might be behind it. In particular, the ghc I installed was with ghcup after haskell/ghcup-hs#1032, supporting the hypothesis that it's GHC's calling the linker that was at issue. Testing...

[hseg]

OK, it indeed seems to be a GHC issue rather than a cabal issue, sorry for the noise.
To reproduce, for pkg in [network, unix, time], cabalVer in [3.10.2.1,3.10.3.0] and ghcVer in [9.6.4]:

ghcup install ghc "$ghcVer" -- --enable-ld-override
ghcup install cabal "$cabalVer"
ghcup set ghc "$ghcVer"
ghcup set cabal "$cabalVer"
export LDFLAGS='-Wl,-z,pack-relative-relocs'
git clone https://github.com/haskell/"$pkg"
cd "$pkg"
autoreconf -i
cabal configure
cabal build

With these parameters, I can reproduce (eg for unix):

Build profile: -w ghc-9.6.4 -O1
In order, the following will be built (use -v for more details):
 - unix-2.8.5.1 (lib:unix, test:FdReadBuf001, test:ForkProcess01, test:Posix004, test:Posix009, test:Posix014, test:PutEnv001, test:ResourceLimit, test:Semaphore001, test:Semaphore002, test:SemaphoreInterrupt, test:Signals002, test:Signals004, test:T13660, test:T8108, test:Terminal, test:unix-tests) (first run)
Configuring unix-2.8.5.1...
configure: WARNING: unrecognized options: --with-compiler
checking for gcc... /usr/bin/gcc
checking whether the C compiler works... no
configure: error: in '/tmp/unix/dist-newstyle/build/x86_64-linux/ghc-9.6.4/unix-2.8.5.1/build':
configure: error: C compiler cannot create executables
See 'config.log' for more details
Error: cabal: Failed to build unix-2.8.5.1. The failure occurred during the
configure step. The build process terminated with exit code 77

It's quite probable nothing needs to be done here, but I leave the closure decision to you.

[gbaz]

Seems to be resolved upstream: https://gitlab.haskell.org/ghc/ghc/-/commit/32a8103f3b3e22907fdd67b69c919c5251d8cc20

Let's optimistically close.

[andreabedini]

OK, it indeed seems to be a GHC issue rather than a cabal issue, sorry for the noise.

Nothing to be sorry about. It's a common misconception that cabal invokes the linker. In the most common cases it doesn't and linking is left to ghc.