Merge branch 'mr/fix-linker-warnings-with-lld' into 'master'

Fix linker warnings when using lld

See merge request eng/toolchain/bb-runtimes!139

aarch64/__init__.py

@@ -95,13 +95,19 @@ def amend_rts(self, rts_profile, conf):
     def dump_runtime_xml(self, rts_name, rts):
         cnt = super(Aarch64Target, self).dump_runtime_xml(rts_name, rts)
         if rts_name == "embedded":
-            cnt = cnt.replace(
-                '"-nostartfiles"',
-                (
-                    '"-u", "_Unwind_Find_FDE", "-Wl,--eh-frame-hdr",\n'
-                    '        "-nostartfiles"'
-                ),
-            )
+            if using_llvm_compiler():
+                cnt = cnt.replace(
+                    '"-nolibc"',
+                    '"-Wl,--eh-frame-hdr", "-nolibc"',
+                )
+            else:
+                cnt = cnt.replace(
+                    '"-nostartfiles"',
+                    (
+                        '"-u", "_Unwind_Find_FDE", "-Wl,--eh-frame-hdr",\n'
+                        '         "-nostartfiles"'
+                    ),
+                )
         return cnt
 
 
@@ -309,3 +315,6 @@ def __init__(self, uart_io):
 
         self.add_linker_script("aarch64/morello/common.ld")
         self.add_linker_script("aarch64/morello/ram.ld", loader="RAM")
+
+        if using_llvm_compiler():
+            self.add_linker_switch("-nostartfiles")

support/bsp_sources/target.py

@@ -374,8 +374,13 @@ def dump_runtime_xml(self, rts_name, rts):
             # For the Light and Light Tasking runtimes we have the choice of
             # either using libgcc or our Ada libgcc replacement. For the
             # later choice we do not link with any of the standard libraries.
+            #
+            # LLVM doesn't use start files on most bareboard targets, so we
+            # don't pass "-nostartfiles" to avoid a linker warning.
             if rts.rts_vars["Certifiable_Packages"] == "yes":
                 ret += blank + '"-nostdlib",'
+            elif using_llvm_compiler():
+                ret += blank + '"-nolibc",'
             else:
                 ret += blank + '"-nostartfiles", "-nolibc",'
         else:
@@ -385,22 +390,30 @@ def dump_runtime_xml(self, rts_name, rts):
             # interdependencies between libgnarl and libgnat, so we need to
             # force -lgnarl at link time, always.
             #
-            # We provide the link arguments for libc ourselves. Inhibit the
-            # gcc mechanism doing so with -nolibc first. Then we need to
-            # account for intricacies in dependencies, e.g. libc depends on
-            # libgcc as everyone, libgcc on libc for strlen, libgnat on libc
-            # for __errno or other, libc on libgnat for sbrk, libgnat and
-            # libgnarl on each other...
-
-            ret += (
-                blank
-                + '"-nostartfiles", "-nolibc", '
-                + (
-                    '"-Wl,--start-group,-lgnarl,-lgnat,-lc,-lgcc,-lgcc_eh,--end-group",'
-                    if not using_llvm_compiler()
-                    else '"-Wl,--start-group,-lgnarl,-lgnat,-lc,-lunwind,--end-group",'
+            # With gcc, we provide the link arguments for libc ourselves.
+            # Inhibit the gcc mechanism doing so with -nolibc first. Then we
+            # need to account for intricacies in dependencies, e.g. libc
+            # depends on libgcc as everyone, libgcc on libc for strlen,
+            # libgnat on libc for __errno or other, libc on libgnat for sbrk,
+            # libgnat and libgnarl on each other...
+            #
+            # The LLVM linker doesn't depend on the order of archive files on
+            # the command line because it remembers defined symbols in
+            # addition to undefined symbols when scanning archives (see
+            # https://lld.llvm.org/NewLLD.html, "Efficient archive file
+            # handling"). We stills want "-nolibc" because it disables
+            # automatic linking of libm.
+
+            if not using_llvm_compiler():
+                ret += (
+                    blank
+                    + '"-nostartfiles", "-nolibc", '
+                    + '"-Wl,--start-group,'
+                    + "-lgnarl,-lgnat,-lc,-lgcc,-lgcc_eh,"
+                    + '--end-group",'
                 )
-            )
+            else:
+                ret += blank + '"-nolibc", "-lgnarl", "-lgnat", "-lc", "-lunwind",'
 
         # Add linker paths (only needed for bare-metal runtimes)
         if not self.is_os_target: