kavon/llvm-statepoint-utils

Runtime support for LLVM's GC Statepoints

llvm-statepoint-utils's Issues

Asking the difference between the statepoint and safepoint

Hi @kavon,

First of all, I need to thank you for this great job.

I have started on working GC related things and currently I am trying to understand the LLVM GC framework support. When I read the LLVM docs pointed in readme, I found two terms statepoint and safepoint. Could you please explain me the difference between these two?

Non-indirect locations end up as bogus stack frame offsets.

Sometimes, LLVM will re-materialize GC root that it has proven to be a constant (that is obviously not a pointer) instead of saving it to the stack frame. Thus, the "relocation" entry in the emitted stackmap data is a Constant and not an Indirect, which is a frame location:

LBB42_43:                               ## %else_cfgE935_1391E
	movq	%r8, 8(%rsp)
	movq	%r14, 16(%rsp)
	movl	$1, %edi                   # <<< this is a root
	movl	$1, %eax
	movl	$1, %r10d
	movq	%r8, %r12
	callq	_lp_cfgE30B_FD42
Ltmp153:
	movl	$1, %edi                      # <<< this is a root rematerialized.
	movq	8(%rsp), %r10
	movq	16(%rsp), %rcx
	jmp	LBB42_11

Of course, our hash table generator does not expect such things, and just puts a bogus offset in the table instead of crashing the program or warning.

	** frame #1**
		return address: 0x1000091ED
		frame size: 56
		num live ptrs: 3
		ptr slot #0 { kind: base ptr, frame offset: 123456789 }
		ptr slot #1 { kind: base ptr, frame offset: 16 }
		ptr slot #2 { kind: base ptr, frame offset: 8 }

C++ support

The header needs a compound linkage specification (extern "C" {..}) wrapped around it.

example program

im trying to make a gc using this tool, but can't seem to get wailking the stack right. An example program would be great for this. I already looked at the test folder but it did not help me enough.

If this is out of scope of this project please ignore.