[LLVMdev] How to extract the starting address of each basic block with llvm? (original) (raw)

Petsas Athanasios petsas at ics.forth.gr
Fri Mar 28 13:04:37 PDT 2014

Thank you very much Jevin for the suggestion!

But how I can use blockaddress function? Do I have to write a pass in order to use it? As I told you I am new in llvm. Could you provide me a guide or an example?

Thank you very much, Thanasis

On Fri, Mar 28, 2014 at 8:27 PM, Jevin Sweval <jevinsweval at gmail.com> wrote:

On Fri, Mar 28, 2014 at 1:15 PM, Petsas Athanasios <petsas at ics.forth.gr> wrote: > Dear all, > > I use the clang frontend to produce the control flow graph of a C program > through > this command: > clang -Xclang -analyze -Xclang -analyzer-checker=debug.DumpCFG test.c > > The produced information contains all the basic blocks identified by labels, > e.g. B1, B2, etc. along with their predecessors and successors. > > Is there a way to get the starting address of each of these basic block? > I would like to map the basic block labels produced by CFG with the actual > corresponding basic block starting addresses. > > Could I use llvm to do this? From what I understand this issued is > unrelevant with > IR. Maybe I could get something from the machine code (MC). Perhaps > I have to write a pass for llvm backend. Maybe I could get this information > from > BranchFolder and IfConverter machine function passes: > http://llvm.org/docs/WritingAnLLVMBackend.html#branch-folding-and-if-conversion > but I am not sure. > > I am new to llvm so I need some help, > > Thank you, >

Check out blockaddress(@function, %block) as documented in: http://llvm.org/docs/LangRef.html#addresses-of-basic-blocks The documentation says it only has defined behavior when used with indirectbr, but I have been able to store the block address in a global variable that survives lowering and is the correct address. GlobalVariable *GV = new GlobalVariable(M, bbPtr, /isConstant=/true, GlobalValue::ExternalLinkage, BlockAddress::get(bb), name); Beware, the IR BB may be optimized away when lowering to assembly. You can detect this case when blockaddress() returns 1. Cheers, Jevin

-- Thanasis Petsas Distributed Computing Systems (DCS) Institute of Computer Science (ICS/FORTH) Heraklion, Crete Greece (GR)

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