Intel® Distribution for GDB* 2022 Release Notes

Where to Find the Release

Intel® Distribution for GDB* is available as part of the Intel® oneAPI Base Toolkit. To download the Intel® oneAPI Base Toolkit and learn more about toolkits, visit the Intel® Toolkits main page.

Visit Intel® Toolkit and Component Versioning Schema for more information about semantic versioning and how it is used with Intel® oneAPI.

Release Notes for Linux* OS

Major Features

• Multi-target: The debugger can orchestrate multiple targets of different architectures. This feature allows you to debug the "host" portion and the "kernel" of a DPC++ program in the same GDB* session.
• Auto-attach: The debugger automatically creates an inferior that attaches itself to the Intel® Graphics Technology target to be able to receive events and control the GPU for native debugging.
• Thread SIMD lanes: The debugger displays SIMD lane information for the GPU threads on the command line interface. You can switch between lanes.
• Support for debugging a kernel offloaded to a CPU, GPU, or FPGA-emulation device.
• The debugger is based on the GDB* 11.2 release.

Key Capabilities

• Support for Intel® Iris® X^e Graphics.
• Automatically detecting JIT-compiled, or dynamically loaded, kernel code for debugging.
• Defining breakpoints (both inside and outside of a kernel) to halt the execution of the program.
• Inspecting and changing the values of variables in the application.
• Inspecting and changing register values.
• Listing the threads; switching the current thread context.
• Listing active SIMD lanes; switching the current SIMD lane context per thread.
• Evaluating and printing the values of expressions in multiple threads and SIMD lane contexts.
• Disassembling the machine instructions.
• Displaying and navigating the function call-stack.
• Source- and instruction-level stepping.
• Non-stop and all-stop debug mode.
• Recording the execution using Intel® Processor Trace (Intel® PT).
• Printing of Intel® PT PTWRITE payloads in the instruction history and function-call history.
• Displaying the shadow stack backtrace and Intel® Control-flow Enforcement Technology (Intel® CET) debugging status information.

System Requirements

• General hardware requirements: Intel® oneAPI Base Toolkit System Requirements.
• Specific system requirements: Intel® Distribution for GDB* System Requirements.

Documentation

• To set up the debugger, refer to the Get Started with Debugging Data Parallel C++. 
• To follow basic debugging scenarios, refer to the Tutorial.
• To see common Intel® Distribution for GDB* commands, refer to the Reference Sheet.

Changes in 2022.3.1 Release 

• Intel® Distribution for GDB* 2021.7.1 has been updated to include functional and security updates. Users should update to the latest version as it becomes available.

Known Issues and Limitations

• Intel® Distribution for GDB*, version 2022.3 does not include the latest functional and security updates. Intel® Distribution for GDB*, Version 2023.0 will include additional functional and security updates. Customers should update to the latest version as it becomes available.

• For OpenMP* #pragma omp single blocks in C++, private variables cannot be inspected and breakpoints may occasionally not hit the expected line.

• During the expression evaluation, an element of an accessor object cannot be accessed using the multi-dimensional access syntax. See an error example below:

(gdb) print anAccessor[5][3][4]
Cannot resolve function operator[] to any overloaded instance

You can use the id object instead:

(gdb) print workItemId
$1 = cl::sycl::id<3> = {5, 3, 4}
(gdb) print anAccessor[workItemId]
$2 = 1234

• With kernels older than 5.9, hanging behavior may be seen for devices with id 0x3E98. The GPU can be programmatically reset for recovery.

On GPU devices:

• Inferior calls (invocation of kernel functions from inside the debugger for expression evaluation) are not supported.

• GDB might occasionally return the message "Cannot execute this command while the target is running". Ignore the message as it should not affect further debugging.
• If you define a breakpoint at a location before a kernel (inside the host code), the breakpoint is also defined at the start of the kernel. This is similar to defining a breakpoint at a comment line or an empty line: in these cases, the breakpoint is defined for the next source line.
• If the currently selected SIMD lane of a thread becomes inactive, GDB might silently switch the focus to the first active SIMD lane in this thread.
• For Gen12 devices, the number of SIMD lanes is incorrectly shown.
• Ahead-of-time compilation is supported but the code must be built with the -cl-kernel-debug-enable flag.
• Inspecting shared-local-memory (SLM) is not supported.
• Applications that use unified shared memory (USM) may appear as raising a SIGSEGV when a USM-allocated memory is being accessed. This is a mechanism used by the runtime to trigger memory migration. In such cases, sending the signal back to the application resumes the program. For this, use GDB's signal SIGSEGV command.
• Restarting the debugged program while the current context is the host inferior may cause GDB and gdbserver-gt to become out-of-sync. This may require a complete restart of the debugging session to regain the full debugging ability.
• backtrace may fail with error PC not saved, when inside OpenMP parallel for loop with a large number of iterations. To get proper backtrace, limit the number of parallel threads in the loop by using num_teams and thread_limit.

On CPU and GPU devices:

•  Debugging OpenMP kernel code for Fortran (#pragma omp target) is not supported.

Release Notes for Windows* OS

Major Features

• Support for debugging a kernel offloaded to a CPU, GPU, or FPGA-emulation device.

• Integration into Microsoft Visual Studio* interface to enable GPU remote debugging. This feature allows you to debug the "host" portion and the "kernel" of a DPC++ program in the same VS remote debugging session. 

Key Capabilities

• Inserting a breakpoint inside a kernel and stopping when the breakpoint is hit by a thread
• Inspecting local variables
• Source-level stepping
• Backtracing function calls
• Examining threads
• Reading registers
• Disassembling
• Automatic launch of gdbserver-gt
• Support for debugging OpenCL and DPC++ programs
• Support for debugging OpenMP* C++ kernel code for CPU and GPU offloads.
• Ability to connect and debug a target outside the domain network.

System Requirements

• General hardware requirements: Intel® oneAPI Base Toolkit System Requirements.
• Specific system requirements: Intel® Distribution for GDB* System Requirements.

You can download the latest driver at Intel® Graphics - Windows® 10 DCH Driver.

Documentation

To set up the debugger, refer to the Get Started with Debugging Data Parallel C++. If you are more comfortable with the video format, refer to the getting started video.

Changes in 2022.3.1 Release 

• Intel® Distribution for GDB* 2021.7.1 has been updated to include functional and security updates. Users should update to the latest version as it becomes available.

Known Issues and Limitations

On GPU devices:

• The target system might lose the network connection after the debugging session is started. In this case, reboot the target system.
• Microsoft Visual Studio* interface does not support viewing SIMD lanes.
• In Microsoft Visual Studio*, the following message might be displayed "Cannot execute this command while the target is running". Ignore the message as it should not affect further debugging.
• If you define a breakpoint at a location before the kernel (inside the host code), the breakpoint is also defined at the start of the kernel. This is similar to defining a breakpoint at a comment line or an empty line: in these cases, the breakpoint is defined for the next source line.
• After hitting a breakpoint defined before a kernel, not all threads hit a breakpoint defined inside the kernel.
• Single steps on the last line of a kernel lead to the termination of the program being debugged.
• For debugging on a GPU, you should use a grid size of 256 or fewer work items.
• Inferior calls (invocation of kernel functions from inside the debugger for expression evaluation) are not supported.
• Kernel functions are inlined by the compiler. Breakpoints on calls to inlined functions may not be hit. Try placing breakpoints before the call or inside the called function​.
• For OpenMP you need to start the gdbserver-gt manually with IPv4:

$ gdbserver-gt --hostpid=1 --attach 127.0.0.1:1234 1

• backtrace may fail with error PC not saved, when inside OpenMP parallel for loop with a large number of iterations. To get proper backtrace, limit the number of parallel threads in the loop by using num_teams and thread_limit.

On CPU and GPU devices:

•  Debugging OpenMP kernel code for Fortran (#pragma omp target) is not supported.
• For OpenMP #pragma omp single blocks in C++, private variables cannot be inspected and breakpoints may occasionally not hit the expected line.

On FPGA emulator devices:

• For debugging on FPGA emulator, ahead-of-time (AoT) compilation is not supported. Ensure that in Project Properties > DPC++   Enable FPGA Workflows is set to no.

• For debugging on an FPGA emulator, no support for OpenMP.

On CPU devices and FPGA emulator devices:

• It is recommended to disable the GPU debugger for smooth debugging on CPU and FPGA emulator devices.

Previous oneAPI Releases

• 2021 Release notes are available: Intel® Distribution for GDB* 2021 Release Notes 

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