[LLVMdev] Fail to load a pointer to a function inside MCJIT-ed code when it is reload from ObjectCache

[Cheng Zhu]

Hi, All

I have a problem to reuse mcjit jitted code loaded from ObjectCache from a
file. In the first run, I use MCJIT generate function JittedOpExpr object
code as following and it runs OK. 0x7fe4801fa1f8 at instruction
0x00007fe4cc6c2014 points to 0x69382E which is the beginning of ExecEvalVar
function. Then I save the object code into a file after implementing
notifyObjectCompiled method.


                    IrExprGetValue:
0x00007fe4cc6c2000:   push %rbp
0x00007fe4cc6c2001:   mov %rsp,%rbp
0x00007fe4cc6c2004:   mov 0x10(%rdi),%rax
0x00007fe4cc6c2008:   pop %rbp
0x00007fe4cc6c2009:   jmpq *%rax
0x00007fe4cc6c200b:   nopl 0x0(%rax,%rax,1)
                    JittedOpExpr:
0x00007fe4cc6c2010:   push %rbp
0x00007fe4cc6c2011:   mov %rsp,%rbp
*0x00007fe4cc6c2014:   movabs $0x7fe4801fa1f8,%rax*
0x00007fe4cc6c201e:   movabs $0x7fe4801fa1e8,%rdi
0x00007fe4cc6c2028:   callq *(%rax)
0x00007fe4cc6c202a:   add $0x5,%rax
0x00007fe4cc6c202e:   pop %rbp
0x00007fe4cc6c202f:   retq
0x00007fe4cc6c2030:   adc $0x0,%al
0x00007fe4cc6c2032:   add %al,(%rax)
0x00007fe4cc6c2034:   add %al,(%rax)

*0x7fe4801fa1f8 -> 0x69382E*
*                    ExecEvalVar*(ExprState*, ExprContext*, bool*,
ExprDoneCond*):
0x000000000069382e:   push %rbp
0x000000000069382f:   mov %rsp,%rbp
0x0000000000693832:   push %r12

In the next run, I buildedunction of JittedOpExpr again and loaded compiled
object from that saved binary file using getObject and went through
getPointertoFunction from MCJIT execution engine, I got the following
object code in memory. But this time 0x7fe4801fa1f8 points to 0x0, so when
callq *(%rax) it couldn't find the ExecEvalVar anymore. I followed the blog
"Object Caching with the Kaleidoscope Example Problem" written by Andy
Kaylor by implementing my own MCJITObjectCache class. Did I miss anything
here? Thank you very much.

                    IrExprGetValue:
0x00007fe4cc6c2000:   push %rbp
0x00007fe4cc6c2001:   mov %rsp,%rbp
0x00007fe4cc6c2004:   mov 0x10(%rdi),%rax
0x00007fe4cc6c2008:   pop %rbp
0x00007fe4cc6c2009:   jmpq *%rax
0x00007fe4cc6c200b:   nopl 0x0(%rax,%rax,1)
                    JittedOpExpr:
0x00007fe4cc6c2010:   push %rbp
0x00007fe4cc6c2011:   mov %rsp,%rbp
*0x00007fe4cc6c2014:   movabs $0x7fe4801fa1f8,%rax*
0x00007fe4cc6c201e:   movabs $0x7fe4801fa1e8,%rdi
0x00007fe4cc6c2028:   callq *(%rax)
0x00007fe4cc6c202a:   add $0x5,%rax
0x00007fe4cc6c202e:   pop %rbp
0x00007fe4cc6c202f:   retq

*but 0x7fe4801fa1f8 -> 000000000*

-- 
Best regards

Cheng
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