[Git][ghc/ghc][wip/ghc-9.10] driver: always merge objects when possible

[Matthew Pickering (@mpickering)]

Matthew Pickering pushed to branch wip/ghc-9.10 at Glasgow Haskell Compiler / GHC


Commits:
d5f45368 by Cheng Shao at 2024-05-08T09:39:29+01:00
driver: always merge objects when possible

This patch makes the driver always merge objects with `ld -r` when
possible, and only fall back to calling `ar -L` when merge objects
command is unavailable. This completely reverts !8887 and !12313,
given more fixes in Cabal seems to be needed to avoid breaking certain
configurations and the maintainence cost is exceeding the behefits in
this case :/

(cherry picked from commit 631cefec222e2db951c58db0b15a8d80ef5549cb)

- - - - -


1 changed file:

- compiler/GHC/Driver/Pipeline/Execute.hs


Changes:

=====================================
compiler/GHC/Driver/Pipeline/Execute.hs
=====================================
@@ -1040,13 +1040,17 @@ this is accomplished with the `ld -r` command. We rely on this for two ends:
 The command used for object linking is set using the -pgmlm and -optlm
 command-line options.
 
-Sadly, the LLD linker that we use on Windows does not support the `-r` flag
-needed to support object merging (see #21068). For this reason on Windows we do
-not support GHCi objects.  To deal with foreign stubs we build a static archive
-of all of a module's object files instead merging them. Consequently, we can
-end up producing `.o` files which are in fact static archives. However,
-toolchains generally don't have a problem with this as they use file headers,
-not the filename, to determine the nature of inputs.
+However, `ld -r` is broken in some cases:
+
+ * The LLD linker that we use on Windows does not support the `-r`
+   flag needed to support object merging (see #21068). For this reason
+   on Windows we do not support GHCi objects.
+
+In these cases, we bundle a module's own object file with its foreign
+stub's object file, instead of merging them. Consequently, we can end
+up producing `.o` files which are in fact static archives. This can
+only work if `ar -L` is supported, so the archive `.o` files can be
+properly added to the final static library.
 
 Note that this has somewhat non-obvious consequences when producing
 initializers and finalizers. See Note [Initializers and finalizers in Cmm]
@@ -1072,7 +1076,7 @@ via gcc.
 -- | See Note [Object merging].
 joinObjectFiles :: HscEnv -> [FilePath] -> FilePath -> IO ()
 joinObjectFiles hsc_env o_files output_fn
-  | can_merge_objs && not dashLSupported = do
+  | can_merge_objs = do
   let toolSettings' = toolSettings dflags
       ldIsGnuLd = toolSettings_ldIsGnuLd toolSettings'
       ld_r args = GHC.SysTools.runMergeObjects (hsc_logger hsc_env) (hsc_tmpfs hsc_env) (hsc_dflags hsc_env) (



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/d5f453687549b700acf84a0cefed0efd7e274224

-- 
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/d5f453687549b700acf84a0cefed0efd7e274224
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