[llvm-dev] Getting stack size of compiled functions from LLVM

[Sanjoy Das via llvm-dev]

If you don't want to modify LLVM, you can consider inserting a "dummy"
patchpoint or statepoint call in your function.  Then the JIT
generated in-memory object file will contain a __llvm_stackmaps
section that will contain the stack sizes of all the functions in the
module that have a compile-time constant sized stack.  You could also
look into adding a flag that would ask LLVM to always produce this
__llvm_stackmaps section, even if the module did not have any
statepoint or patchpoint calls.

See https://llvm.org/docs/StackMaps.html

-- Sanjoy

On Tue, May 29, 2018 at 10:41 AM, Friedman, Eli via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> On 5/28/2018 11:34 PM, Nicholas Chapman via llvm-dev wrote:
>>
>> Hi all,
>> I'm trying to get the amount of stack memory used by the functions I am
>> JIT compiling with LLVM.
>> I have a host C++ program, and I want to be able to access the stack size
>> from the host C++ program.
>>
>> I see in PrologEpilogInserter.cpp that the computed stack size is read
>> from the MachineFunction corresponding to a Function, in order to issue a
>> warning if the stack size is too large.
>> However I don't see a way to access this information from my host C++
>> program.
>
>
> You can retrieve those warnings from your host program; if you call
> LLVMContext::setDiagnosticHandler, the DiagnosticInfoStackSize gets passed
> to your code instead of getting dumped to stderr.
>
>>
>> One approach I have investigated is writing a MachineFunctionPass that
>> could access the MachineFunctions and hence the stack size. However I have
>> not been able to get my MachineFunctionPass to run
>> without hitting assert failures.
>>
>> Is it possible to add/schedule a MachineFunctionPass to run without
>> modifying the LLVM libraries themselves?  I would prefer not to have to
>> modify LLVM.
>> If it is the case that the code to schedule the MachineFunctionPass must
>> be added to LLVM, then it's not clear to me how to return the stack size
>> information to the host C++ program either.
>
>
> There currently aren't any hooks for this, but it probably wouldn't be hard
> to implement, if you're interested in contributing upstream.  (See
> PassManagerBuilder::addExtension for IR optimization passes.)
>
> -Eli
>
> --
> Employee of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux
> Foundation Collaborative Project
>
>
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