Clang Whole Program Analysis Essays

[cfe-dev] [analyzer] Whole Program Analysis - Full Call Graph

Yury Gribov via cfe-devcfe-dev at lists.llvm.org
Tue Dec 1 08:29:02 PST 2015
On 12/01/2015 03:23 PM, Aleksei Sidorin via cfe-dev wrote: > Hello Phil, >> I met this problem while implementing inter-unit analysis > proof-of-concept for CSA. I'll describe my solution here. As I > understand, this problem cannot be solved inside CSA, so I used > multi-step approach. >> First, for all translation units we should collect a list of 'required' > and 'exported' functions. To build a list of required declarations, we > iterate over AST to find CallExprs that use callee decl without body. To > build a list of exported declarations we just dump all the functions > that are visible externally. >> I used a simple text signature of function as >mangled_name at target_triple_arch for dumping. I used additional arch mark > to distinguish between functions in multi-arch builds. >> Note that some function may be defined in a headers. One should not > merge them because they may have different bodies due to macro > expansion. These calls are local and the approach below should solve > this problem. >> After this, we have two lists. List of required functions is just a list > of signatures; list of external functions is a list of entries looking > like a map: function_signature::file_name at target_triple_arch. Final > export map contains items from exported functions whose key was listed > in required functions. Resulting mapping is an inter-unit call graph. You might also want to track linker calls and then model static/dynamic linking when matching symbols to improve precision and avoid collisions. > You may also need to use C++ mangling-style for C if you build multiple > projects that may contain functions with the same name. However, if you > need to do this, you may need more complicated approach. >> You can take a look at the code. This code also dumps local calls but > marks as local explicitly so it may be used to build a whole program > call graph. You can find our github repo at >https://github.com/haoNoQ/clang/tree/summary-ipa-draft. See > tools/clang-func-mapping > (https://github.com/haoNoQ/clang/blob/summary-ipa-draft/tools/clang-func-mapping/ClangFnMapGen.cpp) > and tools/scan-build/xtu-analyze.py > (https://github.com/haoNoQ/clang/blob/summary-ipa-draft/tools/scan-build/xtu-analyze.py) > for some code. >> Hope it will help. >>> Hello cfe-dev, >>>> I am interested in researching possible static analyzer schemes on whole >> program states. Initially I would like to build a whole program call >> graph. I plan to develop program wide checkers for calls to a >> proprietary SDK. To begin with these checkers would rely on simple call >> graph/AST based analysis rather than ‘full’ static analysis. These >> checkers would include items like simple flow analysis of SDK calls that >> should occur in a particular order (e.g. open()/read()/write()/close()). >> I would be very grateful if anyone can offer any guidance as to how to >> achieve this. >>>> My initial thoughts are to use the current AST call graph feature within >> clang. I would create a checker that builds and serialises the call >> graph to a file for each source file. I plan to add this serialisation >> to the clang CallGraph class along the lines of the current AST >> serialisation. The available serialised call graph files would >> subsequently be read and a merged, creating a full program graph (or >> partial program graph if the whole program has not been serialised). >>>> I have a couple of questions regarding development style: >>>> a) Would the clang CallGraph class be the best place for the >> serialisation, or would it better to place it in the checker(s)? >>>> b) For the read and merge process, should this be an external utility or >> use the regular clang executable? >>>> Any feedback most welcome. Thank you for your time. >

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