(original) (raw)

I'm allocating { i8\*, i32 } on the stack, and would like to add this as a GC root, but I'm having trouble figuring this out.

This works as expected:

declare void @llvm.gcroot(i8\*\* %ptrloc, i8\* %metadata)

define i8\* @bar(i8\* %x) gc "shadow-stack" {

entry:

%objptr = alloca i8\*

call void @llvm.gcroot(i8\*\* %objptr, i8\* null)

store i8\* %x, i8\*\* %objptr

%v = load i8\*, i8\*\* %objptr

ret i8\* %v

}

However, when I have this:

define { i8\*, i32 } @foo({ i8\*, i32 } %x) gc "shadow-stack" {

entry:

%objptr = alloca { i8\*, i32 }

%rootptr = bitcast { i8\*, i32 }\* %objptr to i8\*\*

call void @llvm.gcroot(i8\*\* %rootptr, i8\* null)

store { i8\*, i32 } %x, { i8\*, i32 }\* %objptr

%v = load { i8\*, i32 }, { i8\*, i32 }\* %objptr

ret { i8\*, i32 } %v

}

llc says: llvm.gcroot parameter #1 must either be a pointer alloca, or argument #2 must be a non-null constant.

call void @llvm.gcroot(i8\*\* %rootptr, i8\* null)

...and if I do as it asks and add a metadata then I get a crash:

@info = constant i8 1

define { i8\*, i32 } @quux({ i8\*, i32 } %x) gc "shadow-stack" {

entry:

%objptr = alloca { i8\*, i32 }

%rootptr = bitcast { i8\*, i32 }\* %objptr to i8\*\*

call void @llvm.gcroot(i8\*\* %rootptr, i8\* @info)

store { i8\*, i32 } %x, { i8\*, i32 }\* %objptr

%v = load { i8\*, i32 }, { i8\*, i32 }\* %objptr

ret { i8\*, i32 } %v

}

leads llc into this:

Assertion failed: isa(Val) && "cast() argument of incompatible type!", file C:\\Users\\nikod\\src\\llvm\\include\\llvm/Support/Casting.h, line 236

Wrote crash dump file "C:\\Users\\nikod\\AppData\\Local\\Temp\\llc.exe-7b1546.dmp"

#0 0x01a26809 HandleAbort c:\\users\\nikod\\src\\llvm\\lib\\support\\windows\\signals.inc:405:0

#1 0x75804188 (C:\\WINDOWS\\System32\\ucrtbase.dll+0xa4188)

#2 0x75805422 (C:\\WINDOWS\\System32\\ucrtbase.dll+0xa5422)

#3 0x75806dc5 (C:\\WINDOWS\\System32\\ucrtbase.dll+0xa6dc5)

#4 0x75806ce8 (C:\\WINDOWS\\System32\\ucrtbase.dll+0xa6ce8)

#5 0x7580618b (C:\\WINDOWS\\System32\\ucrtbase.dll+0xa618b)

#6 0x75806e26 (C:\\WINDOWS\\System32\\ucrtbase.dll+0xa6e26)

#7 0x013786a6 InsertRootInitializers c:\\users\\nikod\\src\\llvm\\lib\\codegen\\gcrootlowering.cpp:172:0

#8 0x01378d97 \`anonymous namespace'::LowerIntrinsics::PerformDefaultLowering c:\\users\\nikod\\src\\llvm\\lib\\codegen\\gcrootlowering.cpp:249:0

#9 0x01379986 \`anonymous namespace'::LowerIntrinsics::runOnFunction c:\\users\\nikod\\src\\llvm\\lib\\codegen\\gcrootlowering.cpp:195:0

#10 0x016a343c llvm::FPPassManager::runOnFunction(class llvm::Function &) c:\\users\\nikod\\src\\llvm\\lib\\ir\\legacypassmanager.cpp:1513:0

#11 0x016a35e4 llvm::FPPassManager::runOnModule(class llvm::Module &) c:\\users\\nikod\\src\\llvm\\lib\\ir\\legacypassmanager.cpp:1533:0

#12 0x016a382c \`anonymous namespace'::MPPassManager::runOnModule c:\\users\\nikod\\src\\llvm\\lib\\ir\\legacypassmanager.cpp:1590:0

#13 0x016a2e0e llvm::legacy::PassManagerImpl::run(class llvm::Module &) c:\\users\\nikod\\src\\llvm\\lib\\ir\\legacypassmanager.cpp:1693:0

#14 0x01000a62 compileModule c:\\users\\nikod\\src\\llvm\\tools\\llc\\llc.cpp:534:0

#15 0x010059ca main c:\\users\\nikod\\src\\llvm\\tools\\llc\\llc.cpp:289:0

#16 0x01be99e9 \_scrt\_common\_main\_seh f:\\dd\\vctools\\crt\\vcstartup\\src\\startup\\exe\_common.inl:253:0

#17 0x77178744 (C:\\WINDOWS\\System32\\KERNEL32.DLL+0x18744)

#18 0x7737582d (C:\\WINDOWS\\SYSTEM32\\ntdll.dll+0x6582d)

#19 0x773757fd (C:\\WINDOWS\\SYSTEM32\\ntdll.dll+0x657fd)

(This is the same assertion failure that my full code produces, and which lead me to trying out things with minimal case and llc.)

What I can see in the debugger isn't immediately illuminating. Any clues? Am I missing the obvious here?

This is:

LLVM (http://llvm.org/):

LLVM version 4.0.1

DEBUG build with assertions.

Default target: i686-pc-windows-msvc

Host CPU: skylake

Cheers,

-- nikodemus