Subzero: implemented wrapper script to replace calls to calloc()

docs/ASAN.rst

 Using AddressSanitizer in Subzero
 =================================
 
 AddressSanitizer is a powerful compile-time tool used to detect and report
 illegal memory accesses. For a full description of the tool, see the original
 `paper
 <https://www.usenix.org/system/files/conference/atc12/atc12-final39.pdf>`_.
 AddressSanitizer is only supported on native builds of .pexe files and cannot be
 used in production.
 
 In Subzero, AddressSanitizer depends on being able to find and instrument calls
 to various functions such as malloc() and free(), and as such the .pexe file
-being translated must not have had those symbols stripped. Subzero will not
-complain if it is told to translate a .pexe file with its symbols stripped, but
-it will not be able to find calls to malloc() and free(), so AddressSanitizer
-will not work correctly in the final executable.
+being translated must not have had those symbols stripped or inlined. Subzero
+will not complain if it is told to translate a .pexe file with its symbols
+stripped, but it will not be able to find calls to malloc(), calloc(), free(),
+etc., so AddressSanitizer will not work correctly in the final executable.
+
+Furthermore, pnacl-clang automatically inlines calls to calloc(), even with

[Karl, 2016/07/14 17:33:50]

s/calls/some calls/?

Do you know it does this to all calls?

[tlively, 2016/07/14 20:26:14]

Done.

+inlining turned off, so we provide a wrapper script, sz-clang.py, that normally
+just passes its arguments through to pnacl-clang, but adds instrumentation to
+replace calls to calloc() at the source level if it is passed
+-fsanitize-address.
 
 These are the steps to compile hello.c to an instrumented object file::
 
-    pnacl-clang -o hello.nonfinal.pexe hello.c
+    sz-clang.py -fno-inline -fsanitize-address -o hello.nonfinal.pexe hello.c
     pnacl-finalize --no-strip-syms -o hello.pexe hello.nonfinal.pexe
     pnacl-sz -fsanitize-address -filetype=obj -o hello.o hello.pexe
 
 The resulting object file must be linked with the Subzero-specific
 AddressSanitizer runtime to work correctly. A .pexe file can be compiled with
 AddressSanitizer and properly linked into a final executable using
 subzero/pydir/szbuild.py with the --fsanitize-address flag, i.e.::
 
     pydir/szbuild.py --fsanitize-address hello.pexe
 
 Handling Wide Loads
 ===================
 
 Since AddressSanitizer is implemented only in Subzero, the target .pexe may
 contain widened loads that would cause false positives. To avoid reporting such
 loads as errors, we treat any word-aligned, four byte load as a potentially
 widened load and only check the first byte of the loaded word against shadow
 memory.