diff options
Diffstat (limited to 'compiler/GHC/Driver/Pipeline.hs')
| -rw-r--r-- | compiler/GHC/Driver/Pipeline.hs | 68 |
1 files changed, 63 insertions, 5 deletions
diff --git a/compiler/GHC/Driver/Pipeline.hs b/compiler/GHC/Driver/Pipeline.hs index 8386dd9c7e..7276762f0f 100644 --- a/compiler/GHC/Driver/Pipeline.hs +++ b/compiler/GHC/Driver/Pipeline.hs @@ -394,7 +394,56 @@ compileEmptyStub dflags hsc_env basename location mod_name = do -- --------------------------------------------------------------------------- -- Link - +-- +-- Note [Dynamic linking on macOS] +-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +-- +-- Since macOS Sierra (10.14), the dynamic system linker enforces +-- a limit on the Load Commands. Specifically the Load Command Size +-- Limit is at 32K (32768). The Load Commands contain the install +-- name, dependencies, runpaths, and a few other commands. We however +-- only have control over the install name, dependencies and runpaths. +-- +-- The install name is the name by which this library will be +-- referenced. This is such that we do not need to bake in the full +-- absolute location of the library, and can move the library around. +-- +-- The dependency commands contain the install names from of referenced +-- libraries. Thus if a libraries install name is @rpath/libHS...dylib, +-- that will end up as the dependency. +-- +-- Finally we have the runpaths, which informs the linker about the +-- directories to search for the referenced dependencies. +-- +-- The system linker can do recursive linking, however using only the +-- direct dependencies conflicts with ghc's ability to inline across +-- packages, and as such would end up with unresolved symbols. +-- +-- Thus we will pass the full dependency closure to the linker, and then +-- ask the linker to remove any unused dynamic libraries (-dead_strip_dylibs). +-- +-- We still need to add the relevant runpaths, for the dynamic linker to +-- lookup the referenced libraries though. The linker (ld64) does not +-- have any option to dead strip runpaths; which makes sense as runpaths +-- can be used for dependencies of dependencies as well. +-- +-- The solution we then take in GHC is to not pass any runpaths to the +-- linker at link time, but inject them after the linking. For this to +-- work we'll need to ask the linker to create enough space in the header +-- to add more runpaths after the linking (-headerpad 8000). +-- +-- After the library has been linked by $LD (usually ld64), we will use +-- otool to inspect the libraries left over after dead stripping, compute +-- the relevant runpaths, and inject them into the linked product using +-- the install_name_tool command. +-- +-- This strategy should produce the smallest possible set of load commands +-- while still retaining some form of relocatability via runpaths. +-- +-- The only way I can see to reduce the load command size further would be +-- by shortening the library names, or start putting libraries into the same +-- folders, such that one runpath would be sufficient for multiple/all +-- libraries. link :: GhcLink -- interactive or batch -> DynFlags -- dynamic flags -> Bool -- attempt linking in batch mode? @@ -1787,9 +1836,12 @@ linkBinary' staticLink dflags o_files dep_units = do rc_objs <- maybeCreateManifest dflags output_fn - let link = if staticLink - then GHC.SysTools.runLibtool - else GHC.SysTools.runLink + let link dflags args | staticLink = GHC.SysTools.runLibtool dflags args + | platformOS platform == OSDarwin + = GHC.SysTools.runLink dflags args >> GHC.SysTools.runInjectRPaths dflags pkg_lib_paths output_fn + | otherwise + = GHC.SysTools.runLink dflags args + link dflags ( map GHC.SysTools.Option verbFlags ++ [ GHC.SysTools.Option "-o" @@ -1856,7 +1908,13 @@ linkBinary' staticLink dflags o_files dep_units = do ++ pkg_link_opts ++ pkg_framework_opts ++ (if platformOS platform == OSDarwin - then [ "-Wl,-dead_strip_dylibs" ] + -- dead_strip_dylibs, will remove unused dylibs, and thus save + -- space in the load commands. The -headerpad is necessary so + -- that we can inject more @rpath's later for the left over + -- libraries during runInjectRpaths phase. + -- + -- See Note [Dynamic linking on macOS]. + then [ "-Wl,-dead_strip_dylibs", "-Wl,-headerpad,8000" ] else []) )) |