Segmentation fault with new Linker.Option.CaptureCallState feature

[Jorn Vernee]

Hi,

I've found the issue(s) and submitted a PR here: 
https://github.com/openjdk/panama-foreign/pull/753

We'll probably to get this into JDK20 as well.

Thanks for reporting!

Jorn

On 15/11/2022 01:02, Maurizio Cimadamore wrote:
> Hi Mark,
> many thanks for the bug report (and the kind words :-) ).
>
> This looks like a bug - in the sense that I'm not aware of any 
> limitations in this area. The fact that the function returns a value 
> must be tripping something up in the assembly trampoline we generate.
>
> For now, I've filed this:
>
> https://bugs.openjdk.org/browse/JDK-8296973
>
> Thanks!
> Maurizio
>
> On 14/11/2022 21:56, Mark Schroeder wrote:
>> Hi everyone,
>>
>> first of all, I wanted to thank you for the amazing work you're doing 
>> in this project. I really enjoy working with the API.
>> While experimenting with some system calls under Linux, I encountered 
>> an issue with the new Linker.Option.CaptureCallState feature 
>> delivered here: https://github.com/openjdk/panama-foreign/pull/742. 
>> When calling a function that returns a value (such as a system call 
>> returning -1 in case of an error), the JVM exits due to a 
>> segmentation fault. As a minimal example, I adapted the test code 
>> from the pull request (the issue is not limited to system calls).
>> This is the C code:
>>
>> #include <errno.h>
>> #include <stdint.h>
>>
>> void set_errno(int32_t value) {
>>     errno = value;
>> }
>>
>> int32_t set_errno2(int32_t value) {
>>     errno = (int) value;
>>     return value * 2;
>> }
>>
>> I compiled the code on Linux (Fedora 36) with the following command:
>> gcc -o libCaptureCallState.so -shared -Wall libCaptureCallState.c
>> This is the Java code causing the issue:
>>
>> import java.lang.foreign.FunctionDescriptor;
>> import java.lang.foreign.Linker;
>> import java.lang.foreign.MemoryLayout;
>> import java.lang.foreign.MemorySegment;
>> import java.lang.foreign.MemorySession;
>> import java.lang.foreign.SymbolLookup;
>> import java.lang.foreign.ValueLayout;
>> import java.lang.invoke.MethodHandle;
>> import java.lang.invoke.VarHandle;
>> import java.nio.file.Path;
>>
>> public class TestCaptureCallState {
>>
>>     public static void main(String[] args) throws Throwable {
>> System.load(Path.of("libCaptureCallState.so").toAbsolutePath().toString()); 
>>
>>         Linker linker = Linker.nativeLinker();
>>         SymbolLookup lookup = SymbolLookup.loaderLookup();
>>         Linker.Option.CaptureCallState state = 
>> Linker.Option.captureCallState("errno");
>>         VarHandle errno = 
>> state.layout().varHandle(MemoryLayout.PathElement.groupElement("errno"));
>>         MethodHandle setErrno = linker.downcallHandle(
>>             lookup.find("set_errno").orElseThrow(),
>>             FunctionDescriptor.ofVoid(ValueLayout.JAVA_INT),
>>             state
>>         );
>>         MethodHandle setErrno2 = linker.downcallHandle(
>>             lookup.find("set_errno2").orElseThrow(),
>>             FunctionDescriptor.of(ValueLayout.JAVA_INT, 
>> ValueLayout.JAVA_INT),
>>             state
>>         );
>>
>>         try (MemorySession session = MemorySession.openConfined()) {
>>             MemorySegment saveSeg = session.allocate(state.layout());
>>             System.out.println("Testing set_errno ...");
>>             setErrno.invoke(saveSeg, 42);
>>             int savedErrno = (int) errno.get(saveSeg);
>>             System.out.printf("errno: %d\n", savedErrno);
>>         }
>>         try (MemorySession session = MemorySession.openConfined()) {
>>             System.out.println("Testing set_errno2 ...");
>>             MemorySegment saveSeg = session.allocate(state.layout());
>>             int result = (int) setErrno2.invoke(saveSeg, 42);
>>             int savedErrno = (int) errno.get(saveSeg);
>>             System.out.printf("errno: %d, result: %d\n", savedErrno, 
>> result);
>>         }
>>     }
>> }
>>
>> I executed the code with the following commands:
>> javac --enable-preview --release 20 TestCaptureCallState.java
>> java --enable-preview --enable-native-access=ALL-UNNAMED 
>> TestCaptureCallState
>> The code fails when calling the function with the return value:
>>
>> Testing set_errno ...
>> errno: 42
>> Testing set_errno2 ...
>> #
>> # A fatal error has been detected by the Java Runtime Environment:
>> #
>> #  SIGSEGV (0xb) at pc=0x00007fea8ed0dce8, pid=47154, tid=47155
>> #
>> # JRE version: OpenJDK Runtime Environment (20.0) (build 
>> 20-internal-adhoc.maschroeder.openjdk--panama-foreign)
>> # Java VM: OpenJDK 64-Bit Server VM 
>> (20-internal-adhoc.maschroeder.openjdk--panama-foreign, mixed mode, 
>> sharing, tiered, compressed oops, compressed class ptrs, g1 gc, 
>> linux-amd64)
>> # Problematic frame:
>> # V  [libjvm.so+0x70dce8]  DowncallLinker::capture_state(int*, int)+0x18
>> ...
>>
>> Is there something that I overlooked? Is this a known limitation of 
>> the new feature?
>>
>> Mark