Use -lxxx internally rather than full library path

Since we already supply the correct `-L` path we can rely on wasm-ld to
find, for example, libc.a by simply pasing `-lc` rather than its full
path.

This is in line with what gcc and clang do.

This is almost NFC, except in that case where the user supplies and
library path via `-L` which happens to contains a file called `libc.a`.
In this case, as with clang or gcc, that file will be chosen over the
system one.

This makes the linker command lines shorter, more readable, more inline
with other compilers.

Author: sbc100

ChangeLog.md

@@ -20,6 +20,12 @@ See docs/process.md for more on how version tagging works.
 
 2.0.24
 ------
+- System libraries are now passed to the linker internally via `-lfoo` rather
+  than using their full path.  This is in line with how gcc and clang pass system
+  libraries to the linker.  This should not effect any builds unless a project a
+  happens to have, for example, a file called `libc.a` in one of its library
+  paths.  This would have the effect of overriding the system library (as it
+  would with gcc or clang) (#14342).
 - CMake projects (those that either use emcmake or use Emscripten.cmake
   directly) are new configured to install (by default) directly into the
   emscripten sysroot.  This means that running `cmake --install` (or running the

embuilder.py

@@ -176,7 +176,9 @@ def main():
       library = SYSTEM_LIBRARIES[what]
       if force:
         library.erase()
-      library.get_path()
+      # This will trigger a build of the library if it doesn't already
+      # exist.
+      library.get_link_flag()
     elif what == 'sysroot':
       if force:
         shared.Cache.erase_file('sysroot_install.stamp')

emcc.py

@@ -462,7 +462,11 @@ def is_supported(f):
         # lld allows various flags to have either a single -foo or double --foo
         if f.startswith(flag) or f.startswith('-' + flag):
           diagnostics.warning('linkflags', 'ignoring unsupported linker flag: `%s`', f)
-          return False, takes_arg
+          # Skip the next argument if this linker flag takes and argument and that
+          # argument was not specified as a separately (i.e. it was specified as
+          # single arg containing an `=` char.)
+          skip_next = takes_arg and '=' not in f
+          return False, skip_next
       return True, False
     else:
       if f in SUPPORTED_LINKER_FLAGS:
@@ -749,11 +753,6 @@ def emsdk_ldflags(user_args):
   if '-nostdlib' in user_args:
     return ldflags
 
-  # TODO(sbc): Add system libraries here rather than conditionally including
-  # them via .symbols files.
-  libraries = []
-  ldflags += ['-l' + l for l in libraries]
-
   return ldflags
 
 

tools/system_libs.py

@@ -292,13 +292,20 @@ def can_build(self):
   def erase(self):
     shared.Cache.erase_file(shared.Cache.get_lib_name(self.get_filename()))
 
-  def get_path(self):
+  def get_link_flag(self):
     """
-    Gets the cached path of this library.
+    Gets the link flags needed to use the library.
 
     This will trigger a build if this library is not in the cache.
     """
-    return shared.Cache.get_lib(self.get_filename(), self.build)
+    fullpath = shared.Cache.get_lib(self.get_filename(), self.build)
+    # For non-libaries (e.g. crt1.o) we pass the entire path to the linker
+    if self.get_ext() != '.a':
+      return fullpath
+    # For libraries (.a) files, we pass the abbreviated `-l` form.
+    base = shared.unsuffixed_basename(fullpath)
+    assert base.startswith('lib')
+    return '-l' + base[len('lib'):]
 
   def get_files(self):
     """
@@ -1486,8 +1493,9 @@ def add_library(libname):
 
     logger.debug('including %s (%s)' % (lib.name, lib.get_filename()))
 
-    need_whole_archive = lib.name in force_include and lib.get_ext() == '.a'
-    libs_to_link.append((lib.get_path(), need_whole_archive))
+    is_archive = lib.get_ext() == '.a'
+    need_whole_archive = lib.name in force_include and is_archive
+    libs_to_link.append((lib.get_link_flag(), need_whole_archive))
 
   if settings.USE_PTHREADS:
     add_library('crtbegin')