Simon Marlow pushed to branch wip/simonmar/rts-ld-options at Glasgow Haskell Compiler / GHC

Commits:

• 06406143
  by Simon Marlow at 2026-11-05T10:57:35+00:00

  Move `-u init_ghc_hs_iface` from the compiler to rts.cabal
  
  Having special flags in `.cabal` files rather than built into the
  compiler is better. I ran into this when trying to build GHC with Buck2,
  which wants to do some linking by itself so would have to replicate the
  magic from the compiler - instead, moving the magic into `rts.cabal`
  keeps it in one place.
  
  But this changes the logic slightly, because previously the magic flag
  was added whenever `ghc-internal` is being linked, whereas with this
  change the magic flag is added whenever `rts` is linked. It seems to me
  the latter is more correct (and this is how it was done prior to #26166,
  which introduced the compiler magic).
  
  I hope this doesn't reintroduce the problem that #26166 was fixing, but
  it's not clear to me exactly what that problem was. There is and always
  has been a recursive dependency between `rts` and `ghc-internal`; the
  fix in #26166 only changed it to a single function symbol reference rather
  than dozens of data references. This fix doesn't change that.
  
  Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
  

3 changed files:

• compiler/GHC/Linker/Executable.hs
• rts/RtsToHsIface.c
• rts/rts.cabal

Changes:

                  ++ pkg_lib_path_opts

                  ++ extraLinkObj

                  ++ noteLinkObjs

-                 -- See Note [RTS/ghc-internal interface]

-                 -- (-u<sym> must come before -lghc-internal...!)

-                 ++ (if ghcInternalUnitId `elem` map unitId pkgs

-                     then [concat [ "-Wl,-u,"

-                                  , ['_' | platformLeadingUnderscore platform]

-                                  , "init_ghc_hs_iface" ]]

-                     else [])

                  ++ pkg_link_opts

                  ++ pkg_framework_opts

                  ++ (if platformOS platform == OSDarwin

  * explicit.

  *

  * Note that the init_ghc_hs_iface symbol is explicitly included in the final

- * binary via the linker flag `-uinit_ghc_hs_iface`, when an executable is

- * linked against ghc-internal by GHC.

+ * binary via the linker flag `-uinit_ghc_hs_iface`, which we put

+ * in the rts package's ld-options.

  *

  * `-uinit_ghc_hs_iface` ensures that the `init_ghc_hs_iface` symbol is

  * included in the final link, even when we link against `ghc-internal.a`

                         stg/Ticky.h

                         stg/Types.h

+      -- The RTS calls init_ghc_hs_iface, which is defined in ghc-internal: see

+      -- Note [RTS/ghc-internal interface] in RtsToHsIface.c.

+      if flag(leading-underscore)

+        ld-options: -Wl,-u,_init_ghc_hs_iface

+      else

+        ld-options: -Wl,-u,init_ghc_hs_iface

+

       if os(osx)

         ld-options: "-Wl,-search_paths_first"

         if !arch(x86_64) && !arch(aarch64)