Merge branch 'master' of github.com:SRI-CSL/whole-program-llvm

Author: Ian A.Mason

README.md

@@ -251,6 +251,14 @@ cross-compiling you must ensure to use the appropriate `objcopy` for the target
 architecture. The `BINUTILS_TARGET_PREFIX` environment variable can be used to
 set the objcopy of choice, for example, `arm-linux-gnueabihf`.
 
+LTO Support
+-----------
+
+In some situations it is desirable to pass certain flags to clang in the step that
+produces the bitcode. This can be fulfilled by setting the 
+`LLVM_BITCODE_GENERATION_FLAGS` environment variable to the desired 
+flags, for example `"-flto -fwhole-program-vtables"`.
+
 Debugging
 ---------
 

doc/tutorial-ubuntu-16.04.md

@@ -74,7 +74,14 @@ Extract the bitcode.
 >ls -la httpd.bc
 -rw-r--r-- 1 vagrant vagrant 1119584 Aug  4 20:02 httpd.bc
 ```
+> Note that in httpd-2.4.41, the binary of `httpd` is under directory ".libs",
+    > in that case, please cd into ".libs" then execute the command.
 
+```
+cd .libs
+ls -la httpd
+extract-bc httpd
+```
 ## Step 6.
 
 Turn the bitcode into a second executable binary. (optional -- just for fun and sanity checking)

wllvm/compilers.py

@@ -202,7 +202,13 @@ def getCommand(self):
 class ClangBuilder(BuilderBase):
     def getBitcodeCompiler(self):
         cc = self.getCompiler()
-        return cc + ['-emit-llvm']
+        retval = cc + ['-emit-llvm']
+        # iam: If the environment variable LLVM_BITCODE_GENERATION_FLAGS is set we will add them to the
+        # bitcode generation step
+        bitcodeFLAGS  = os.getenv('LLVM_BITCODE_GENERATION_FLAGS')
+        if bitcodeFLAGS:
+            retval = retval + bitcodeFLAGS.split()
+        return retval
 
     def getCompiler(self):
         if self.mode == "wllvm++":