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Nikodemus Siivola via llvm-dev

2017-Nov-01 09:59 UTC

[llvm-dev] llvm.gcroot trouble with non-i8* allocas

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<X>(Val) && "cast<Ty>() 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
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Nikodemus Siivola via llvm-dev

2017-Nov-01 21:26 UTC

head link

[llvm-dev] llvm.gcroot trouble with non-i8* allocas

Solved by using alloca i8*, i32 2 which the system seems happy enough with,
and bitcasting to the actual type for rest of the code after llvm.gcroot.

Not entirely sure if this is a terrible workaround or exactly the way
gcroot is supposed to be used...


On Wed, Nov 1, 2017 at 11:59 AM, Nikodemus Siivola <
nikodemus at random-state.net> wrote:
> 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<X>(Val) && "cast<Ty>()
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
>
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Philip Reames via llvm-dev

2018-Feb-23 05:10 UTC

head link

[llvm-dev] llvm.gcroot trouble with non-i8* allocas

At this point gcroot is essentially deprecated.  It hasn't been 
officially deprecated and probably won't be in the near future, but the 
only practical user/contributor to LLVM GC support is using statepoint 
and the related infrastructure.  Not saying you need to change your 
approach, but might be something you want to keep in mind.

Philip

On 11/01/2017 02:26 PM, Nikodemus Siivola via llvm-dev
wrote:> Solved by using alloca i8*, i32 2 which the system seems happy enough 
> with, and bitcasting to the actual type for rest of the code after 
> llvm.gcroot.
>
> Not entirely sure if this is a terrible workaround or exactly the way 
> gcroot is supposed to be used...
>
>
> On Wed, Nov 1, 2017 at 11:59 AM, Nikodemus Siivola 
> <nikodemus at random-state.net <mailto:nikodemus at
random-state.net>> wrote:
>
>     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<X>(Val) && "cast<Ty>()
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
>
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

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