limit symbols exported when using --enable-mergelibs

when doing LTO and --enable-mergelibs, we can improve the effectiveness
of LTO by marking more code as internal to the merged library.

So introduce a new macro UNLESS_MERGELIBS, which we can wrap around
*_DLLPUBLIC annotations

Also introduced here is a script that can be run on a completed build to
determine which classes can be marked with this macro.

Change-Id: I73fb87c897489da53791277d0b66b01f884ba061
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/89991
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

1 files changed, 152 insertions, 0 deletions

diff --git a/bin/find-mergedlib-can-be-private.py b/bin/find-mergedlib-can-be-private.py
new file mode 100755
index 000000000000..572cd1c8e005
--- /dev/null
+++ b/bin/find-mergedlib-can-be-private.py
@@ -0,0 +1,152 @@
+#!/usr/bin/python2
+#
+# Generate a custom linker script/map file for the --enabled-mergedlibs merged library
+# which reduces the startup time and enables further optimisations with --enable-lto because 60% or more
+# of the symbols become internal only.
+#
+
+import subprocess
+import sys
+import re
+
+exported_symbols = set()
+imported_symbols = set()
+
+
+# Copied from solenv/gbuild/extensions/pre_MergedLibsList.mk
+# TODO there has to be a way to run gmake and get it to dump this list for me
+merged_libs = { \
+    "avmedia" \
+    ,"basctl" \
+    ,"basprov" \
+    ,"basegfx" \
+    ,"canvasfactory" \
+    ,"canvastools" \
+    ,"comphelper" \
+    ,"configmgr" \
+    ,"cppcanvas" \
+    ,"crashreport)" \
+    ,"dbtools" \
+    ,"deployment" \
+    ,"deploymentmisc" \
+    ,"desktopbe1)" \
+    ,"desktop_detector)" \
+    ,"drawinglayer" \
+    ,"editeng" \
+    ,"expwrap" \
+    ,"filterconfig" \
+    ,"fsstorage" \
+    ,"fwe" \
+    ,"fwi" \
+    ,"fwk" \
+    ,"helplinker)" \
+    ,"i18npool" \
+    ,"i18nutil" \
+    ,"lng" \
+    ,"localebe1" \
+    ,"mcnttype" \
+    ,"msfilter" \
+    ,"mtfrenderer" \
+    ,"opencl" \
+    ,"package2" \
+    ,"sax" \
+    ,"sb" \
+    ,"simplecanvas" \
+    ,"sfx" \
+    ,"sofficeapp" \
+    ,"sot" \
+    ,"spl" \
+    ,"stringresource" \
+    ,"svl" \
+    ,"svt" \
+    ,"svx" \
+    ,"svxcore" \
+    ,"tk" \
+    ,"tl" \
+    ,"ucb1" \
+    ,"ucbhelper" \
+    ,"ucpexpand1" \
+    ,"ucpfile1" \
+    ,"unoxml" \
+    ,"utl" \
+    ,"uui" \
+    ,"vcl" \
+    ,"xmlscript" \
+    ,"xo" \
+    ,"xstor" }
+
+classes_with_exported_symbols = set()
+classes_with_imported_symbols = set()
+
+# look for symbols exported by libmerged
+subprocess_nm = subprocess.Popen("nm -D instdir/program/libmergedlo.so", stdout=subprocess.PIPE, shell=True)
+with subprocess_nm.stdout as txt:
+    # We are looking for lines something like:
+    # 0000000000036ed0 T flash_component_getFactory
+    line_regex = re.compile(r'^[0-9a-fA-F]+ T ')
+    for line in txt:
+        line = line.strip()
+        if line_regex.match(line):
+            exported_symbols.add(line.split(" ")[2])
+subprocess_nm.terminate()
+
+# look for symbols imported from libmerged
+subprocess_find = subprocess.Popen("(find instdir/program/ -type f; ls ./workdir/LinkTarget/CppunitTest/*.so) | xargs grep -l mergedlo",
+        stdout=subprocess.PIPE, shell=True)
+with subprocess_find.stdout as txt:
+    for line in txt:
+        sharedlib = line.strip()
+        s = sharedlib[sharedlib.find("/lib") + 4 : len(sharedlib) - 3]
+        if s in merged_libs: continue
+        # look for imported symbols
+        subprocess_objdump = subprocess.Popen("objdump -T " + sharedlib, stdout=subprocess.PIPE, shell=True)
+        with subprocess_objdump.stdout as txt2:
+            # ignore some header bumpf
+            txt2.readline()
+            txt2.readline()
+            txt2.readline()
+            txt2.readline()
+            # We are looking for lines something like (noting that one of them uses spaces, and the other tabs)
+            # 0000000000000000      DF *UND*  0000000000000000     _ZN16FilterConfigItem10WriteInt32ERKN3rtl8OUStringEi
+            for line2 in txt2:
+                line2 = line2.strip()
+                if line2.find("*UND*") == -1: continue
+                tokens = line2.split(" ")
+                sym = tokens[len(tokens)-1].strip()
+                imported_symbols.add(sym)
+        subprocess_objdump.terminate()
+subprocess_find.terminate()
+
+intersec_symbols = exported_symbols.intersection(imported_symbols)
+print("no symbols exported from libmerged   = " + str(len(exported_symbols)))
+print("no symbols that can be made internal = " + str(len(intersec_symbols)))
+
+# Now look for classes where none of the class symbols are imported,
+# i.e. we can mark the whole class as hidden
+
+def extract_class(sym, add_to_set):
+    filtered_sym = subprocess.check_output(["c++filt", sym]).strip()
+    if filtered_sym.startswith("vtable for "):
+        classname = filtered_sym[11:]
+        add_to_set.add(classname)
+        return
+    if filtered_sym.startswith("non-virtual thunk to "):
+        filtered_sym = filtered_sym[21:]
+    elif filtered_sym.startswith("virtual thunk to "):
+        filtered_sym = filtered_sym[17:]
+    i = filtered_sym.find("(")
+    if i != -1:
+        i = filtered_sym.rfind("::", 0, i)
+        if i != -1:
+            classname = filtered_sym[:i]
+            add_to_set.add(classname)
+
+for sym in exported_symbols:
+    extract_class(sym, classes_with_exported_symbols)
+for sym in imported_symbols:
+    extract_class(sym, classes_with_imported_symbols)
+
+with open("bin/find-mergedlib-can-be-private.classes.results", "wt") as f:
+    for sym in sorted(classes_with_exported_symbols - classes_with_imported_symbols):
+        if sym.startswith("std::") or sym.startswith("void std::"): continue
+        f.write(sym + "\n")