[LLVMdev] Question about jumptable and indirect function call. (original) (raw)

XiaoGuang Wang xjtuwxg at gmail.com
Sun Oct 5 13:47:31 PDT 2014

Hi all,

I'm a beginner in LLVM. I read a paper recently, and I'm trying to use LLVM jumptable in 3.5. When I compile the .bc file into .s file, I tried to use the different jumptable type: all, single, ...

e.g. clang -c -emit-llvm test.c llc test.bc -jump-table-type=full -o test-full.s llc test.bc -jump-table-type=single -o test-single.s

The tested C source code is like: void foo() { printf("foo...\n"); }

void bar() { printf("bar...\n"); }

void foo1(int arg) { printf("foo1... %d..\n", arg); }

void bar1(int arg) { printf("bar1... %d..\n", arg); }

// function pointer void (*fp)() = 0; void (*fp1)(int) = 0;

int main(int argc, char* argv[]) { int input = 0;

printf("Hello\n"); fp = foo; fp(); fp = bar; fp(); fp1 = foo1; fp1(1); fp1 = bar1; fp1(2); }

However, they produced the same .s assembly (test-full.s, test-single.s). I think the llc will produce difference .s files, since I choose the jumptable options. And according to my understanding, the jumptable contains the destination address of each indirect function call. So what's going on with my test. Is there something I did wrong with jumptable options? Or is the jumptable tried to address other problem, not indirect call?

Thanks!

Sincerely, Xiaoguang Wang -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20141005/94ee35c2/attachment.html>

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