llvm dev - Jan 2015 - [LLVMdev] JIT simple module and accessing the value fails

I'm using the llvm-c API and want to use the JIT. I've created the
following
module

; ModuleID = '_tmp'

@a = global i64 5

define i64 @__tempfunc() {
entry:
  %a_val = load i64* @a
  ret i64 %a_val
}

This output is generated by LLVMDumpModule just before I call LLVMRunFunction. 
Which yields a LLVMGenericValueRef. However converting the result to a 64bit 
integer via LLVMGenericValueToInt(gv, true), it results in 360287970189639680 
or something similar - not 5. Converting via LLVMGenericValueToInt(gv, false) 
didn't help either.

How can I use global variables in a JIT situation? Is anything wrong with the 
IR?

On Thursday 08 January 2015 17:11:15 Tobias Pankrath
wrote:
> This output is generated by LLVMDumpModule just before I call
> LLVMRunFunction. Which yields a LLVMGenericValueRef. However converting the
> result to a 64bit integer via LLVMGenericValueToInt(gv, true), it results
> in 360287970189639680 or something similar - not 5. Converting via
> LLVMGenericValueToInt(gv, false) didn't help either.
> 
> How can I use global variables in a JIT situation? Is anything wrong with
> the IR?
> 
Okay, I already figured out that it has to do with the datalayout. How do I 
set it correctly? I'm working on a linux x86_64 and I tried 
LLVMSetDataLayout(mod, "x86_64-pc-linux") which crashes the program
with

    LLVM ERROR: not a number, or does not fit in an unsigned int

Using just LLVMSetDataLayout(mod, "e") solves it for now, would still
like to
know what the correct setting is / why x86_64-pc-linux does not work.

On 1/8/15 9:52 AM, Tobias Pankrath wrote:
> On Thursday 08 January 2015 17:11:15 Tobias Pankrath wrote:
>> This output is generated by LLVMDumpModule just before I call
>> LLVMRunFunction. Which yields a LLVMGenericValueRef. However converting
the
>> result to a 64bit integer via LLVMGenericValueToInt(gv, true), it
results
>> in 360287970189639680 or something similar - not 5. Converting via
>> LLVMGenericValueToInt(gv, false) didn't help either.
>>
>> How can I use global variables in a JIT situation? Is anything wrong
with
>> the IR?
>>
>
> Okay, I already figured out that it has to do with the datalayout. How do I
> set it correctly? I'm working on a linux x86_64 and I tried
> LLVMSetDataLayout(mod, "x86_64-pc-linux") which crashes the
program with
>
>      LLVM ERROR: not a number, or does not fit in an unsigned int
>
> Using just LLVMSetDataLayout(mod, "e") solves it for now, would
still like to
> know what the correct setting is / why x86_64-pc-linux does not work.
"x86_64-pc-linux" is a Triple, not a Data Layout: 
http://llvm.org/docs/LangRef.html#data-layout.

The name "Triple" here lies: 
http://llvm.org/docs/doxygen/html/group__LLVMCCoreModule.html#ga09bb21e82ee1df64fd387cd1498ceded
Looks like a copy-pasta to me.


Jon
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-- 
Jon Roelofs
jonathan at codesourcery.com
CodeSourcery / Mentor Embedded