improve libc++ links

2 files changed, 68 insertions, 30 deletions

diff --git a/xmake/modules/core/tools/clang.lua b/xmake/modules/core/tools/clang.lua
index a79e67142..c264f6656 100644
--- a/xmake/modules/core/tools/clang.lua
+++ b/xmake/modules/core/tools/clang.lua
@@ -205,27 +205,6 @@ function _has_nostdlibxx(self)
     return has_nostdlibxx
 end
 
--- find the static libc++.a / libc++abi.a archives under the llvm library dirs
-function _get_static_cxxlibs(llvm_dirs)
-    local libdirs = {}
-    if llvm_dirs.cxxlibdir then
-        table.insert(libdirs, llvm_dirs.cxxlibdir)
-    end
-    if llvm_dirs.libdir then
-        table.insert(libdirs, llvm_dirs.libdir)
-    end
-    local libcxx, libcxxabi
-    for _, dir in ipairs(libdirs) do
-        if not libcxx and os.isfile(path.join(dir, "libc++.a")) then
-            libcxx = path.join(dir, "libc++.a")
-        end
-        if not libcxxabi and os.isfile(path.join(dir, "libc++abi.a")) then
-            libcxxabi = path.join(dir, "libc++abi.a")
-        end
-    end
-    return libcxx, libcxxabi
-end
-
 -- make the runtime flag
 -- @see https://github.com/xmake-io/xmake/issues/3546
 function nf_runtime(self, runtime, opt)
@@ -319,20 +298,29 @@ function nf_runtime(self, runtime, opt)
                     end
                 end
                 if runtime:endswith("_static") then
-                    -- -static-libstdc++ only pulls in libc++.a, not libc++abi.a, so libc++abi
+                    -- -static-libstdc++ only pulls in libc++.a, not libc++abi.a, so the libc++abi
                     -- symbols (typeinfo, __cxa_*) stay undefined and the link fails, especially
                     -- once c++ modules reference more of libc++.
                     --
-                    -- if we can locate both static archives, link them explicitly in the correct
-                    -- order (libc++.a before libc++abi.a) and disable the driver's automatic c++
-                    -- runtime with -nostdlib++, otherwise fall back to -static-libstdc++.
+                    -- if we can locate both static archives, link them explicitly in a group
+                    -- (they reference each other) and disable the driver's automatic c++ runtime
+                    -- with -nostdlib++, otherwise (bundled abi) fall back to -static-libstdc++.
                     --
                     -- note: target.runtimes is ordered right before the syslinks in the c++ link
                     -- order, so these archives are placed after the object files / user links.
-                    -- @see https://github.com/xmake-io/xmake/issues/7442
-                    local libcxx, libcxxabi = _get_static_cxxlibs(llvm_dirs)
-                    if libcxx and libcxxabi and _has_nostdlibxx(self) then
-                        maps["c++_static"] = table.join(maps["c++_static"], "-nostdlib++", libcxx, libcxxabi)
+                    -- @see https://github.com/xmake-io/xmake/issues/7442, https://github.com/xmake-io/xmake/issues/7656
+                    if llvm_dirs.libcxx_static and llvm_dirs.libcxxabi_static and _has_nostdlibxx(self) then
+                        local cxxlibs = {llvm_dirs.libcxx_static, llvm_dirs.libcxxabi_static}
+                        -- apple ld64 does not support --start-group, it always rescans archives
+                        if not self:is_plat("macosx", "iphoneos", "watchos", "appletvos", "applexros") then
+                            cxxlibs = table.join("-Wl,--start-group", cxxlibs, "-Wl,--end-group")
+                        end
+                        -- -stdlib=libc++ is unused when linking with -nostdlib++, remove it to avoid
+                        -- the `argument unused during compilation` warning
+                        local ldflags = table.remove_if(table.wrap(maps["c++_static"]), function (_, flag)
+                            return flag == "-stdlib=libc++"
+                        end)
+                        maps["c++_static"] = table.join(ldflags, "-nostdlib++", cxxlibs)
                     elseif _has_static_libstdcxx(self) then
                         maps["c++_static"] = table.join(maps["c++_static"], "-static-libstdc++")
                     end
diff --git a/xmake/modules/private/utils/toolchain.lua b/xmake/modules/private/utils/toolchain.lua
index c2840a591..bd673fa0c 100644
--- a/xmake/modules/private/utils/toolchain.lua
+++ b/xmake/modules/private/utils/toolchain.lua
@@ -343,6 +343,25 @@ function map_linkflags_for_package(package, targetkind, sourcekinds, name, value
     return flags
 end
 
+-- ask the clang driver for the absolute path of the given library
+--
+-- clang knows its own library search paths, e.g. the per-target runtime directory
+-- (`lib/<target-triple>/libc++.a`), and it also works when the toolchain has no `--sdk=/xxx/llvm`.
+--
+-- it just echoes back the given filename if the library does not exist,
+-- so we only accept an existing absolute path.
+function _get_llvm_libfile(toolchain, clang, libname, opt)
+    local argv = table.wrap(get_clang_target_flags(toolchain))
+    table.insert(argv, "-print-file-name=" .. libname)
+    local libfile = try {function () return os.iorunv(clang, argv, {envs = opt.envs}) end}
+    if libfile then
+        libfile = path.normalize(libfile:trim())
+        if path.is_absolute(libfile) and os.isfile(libfile) then
+            return libfile
+        end
+    end
+end
+
 -- Check and cache llvm/clang driver info (e.g. -print-resource-dir/-print-target-triple) in toolchain:config().
 -- It must be collected during toolchain on_check so that toolchain on_load can use it without running clang again.
 -- @see https://github.com/xmake-io/xmake/issues/7337#issuecomment-3942499208
@@ -370,6 +389,17 @@ function check_llvm_info(toolchain, clang, opt)
             toolchain:config_set("llvm_target_triple", target_triple)
         end
     end
+
+    -- the static c++ runtime archives, they may be in the per-target runtime directory,
+    -- e.g. `lib/x86_64-unknown-linux-gnu/libc++.a`
+    -- @see https://github.com/xmake-io/xmake/issues/7442
+    for libname, configname in pairs({["libc++.a"] = "llvm_libcxx_static", ["libc++abi.a"] = "llvm_libcxxabi_static"}) do
+        local libfile = _get_llvm_libfile(toolchain, clang, libname, opt)
+        if libfile then
+            dprint("checking for llvm %s ... %s", libname, libfile)
+            toolchain:config_set(configname, libfile)
+        end
+    end
 end
 
 -- get llvm sdk resource directory
@@ -457,6 +487,11 @@ function get_llvm_dirs(toolchain)
         end
 
         local bindir, libdir, cxxlibdir, includedir, cxxincludedir, resourcedir, rtdir, rtlink, rtlibdir
+
+        -- the clang driver has already resolved the static c++ runtime archives on check
+        -- @see check_llvm_info
+        local libcxx_static = toolchain:config("llvm_libcxx_static")
+        local libcxxabi_static = toolchain:config("llvm_libcxxabi_static")
         if rootdir then
             bindir = path.join(rootdir, "bin")
             bindir = os.isdir(bindir) and bindir or nil
@@ -476,6 +511,19 @@ function get_llvm_dirs(toolchain)
                 end
             end
 
+            -- fallback to search the static c++ runtime archives in the library directories
+            if libdir and not (libcxx_static and libcxxabi_static) then
+                local staticdirs = cxxlibdir and {cxxlibdir, libdir} or {libdir}
+                for _, dir in ipairs(staticdirs) do
+                    if not libcxx_static and os.isfile(path.join(dir, "libc++.a")) then
+                        libcxx_static = path.join(dir, "libc++.a")
+                    end
+                    if not libcxxabi_static and os.isfile(path.join(dir, "libc++abi.a")) then
+                        libcxxabi_static = path.join(dir, "libc++abi.a")
+                    end
+                end
+            end
+
             includedir = path.join(rootdir, "include")
             includedir = os.isdir(includedir) and includedir or nil
 
@@ -502,7 +550,9 @@ function get_llvm_dirs(toolchain)
                      resourcedir = resourcedir,
                      rtdir = rtdir,
                      rtlibdir = rtlibdir,
-                     rtlink = rtlink }
+                     rtlink = rtlink,
+                     libcxx_static = libcxx_static,
+                     libcxxabi_static = libcxxabi_static }
         memcache:set(cachekey, llvm_dirs)
       end
       return llvm_dirs