[lldb] Improve FreeBSD support on LLDB

[mchoo7]

These are comprehensive list of tasks aimed for LLVM 23.x release. This aims FreeBSD 14 and above since FreeBSD 13 and below will be EOLed before LLVM 23.1.0 release (see Supported FreeBSD releases).

Note: ppc/ppc64 (big endian 32/64bit PowerPC) support in LLDB is incomplete. The architecture isn't used actively anymore so it is very hard to maintain and test features on it. Thus, I'm not adding support for ppc/ppc64. See freebsd-arch mailing thread for more information.

Userspace Debugging (freebsd)

Architecture support

• ppc64le
• [lldb][Process/FreeBSD] Add riscv64 support #180549

Debugger

• Print TLS data (see [lldb] Handle STT_TLS symbol type in ELF parser #178975)

Deprecation/Removal

• [lldb] Remove mips64 support for FreeBSD #179582, [lldb][Process] Remove mips64 POSIX support #179987, [ReleaseNotes] Announce ending support for FreeBSD 13 and below in 23 #180194
• [lldb] [Process/FreeBSD] Assume minimum is FreeBSD 14 #179587

Misc

• [lldb] [Process/Utility] Update code url for FreeBSD in comments #178556
• lldb on FreeBSD picks the wrong address for functions found in both libc and libsys #180444
• In lldb on FreeBSD thread step-out doesn't always work #180445

Kernel Debugging (FreeBSD-Kernel-Core, previously freebsd-kernel)

Architecture support

• [lldb][Process/FreeBSDKernel] Add arm support #180674
• [lldb][Process/FreeBSDKernel] Fix broken debugging on aarch64 #180222
• [lldb][Process/FreeBSDKernelCore] Add ppc64le support #180669
• [lldb][Process/FreeBSDKernelCore] Add riscv64 support #180670

Debugger

• [lldb][Process/FreeBSDKernel] Print unread message buffer on start #178027
• [lldb] [Process/FreeBSDKernel] Select paniced thread automatically #178069
• [lldb] [Process/FreeBSDKernel] List threads in correct order #178306 [lldb][Process/FreeBSDKernelCore] Fix thread ordering #187976
• [lldb][Process/FreeBSDKernelCore] Implement DoWriteMemory() #183237 [lldb][Process/FreeBSDKernelCore] Implement DoWriteMemory() #183553
• [lldb][Process/FreeBSDKernelCore] Defer actual core loading to DoLoadCore() #186626
• [lldb][Process/FreeBSDKernelCore] Add command for refreshing thread list #188692
• Implement trapframe unwinding
• [lldb][Process/FreeBSDKernelCore] Add assertion for pcb #183969
• [lldb][Process/FreeBSDKernelCore] Improve DoUpdateThreadList() #183981
• [lldb][Process/FreeBSDKernelCore] Set kernel displacement #183975
• Improve error handling in ProcessFreeBSDKernelCore.cpp
• [lldb][FreeBSDKernel] Add missing error checks in DynamicLoader #189250

Testing

• Current Process/FreeBSDKernel testing suite is a few years old and it depends on quirks like patching LLDB codebase which makes testing harder. The goal is to reconstruct a comprehensive testing suite for Process/FreeBSDKernelCore plugin.

Deprecation/Removal

• [lldb][Process/FreeBSDKernel] Remove libfbsdvmcore support #181283

Misc

• [lldb][docs] Add FreeBSD kernel debugging information #179597
• [lldb][Process/FreeBSDKernel] Add links to pcb.h #180267
• [lldb][Process/FreeBSDKernel] Rename to FreeBSDKernelCore #182878

[llvmbot]

@llvm/issue-subscribers-lldb

Author: Minsoo Choo (mchoo7)

Details

These are comprehensive list of tasks aimed for LLVM 23.x release. This aims FreeBSD14 and above since FreeBSD 13 and below will be EOLed before LLVM 23.1.0 release (see [Supported FreeBSD releases](https://www.freebsd.org/security/#sup)).

Userspace Debugging

Architecture support

• ppc64
• ppc64le
• riscv64

Debugger

• Print TLS data (see [lldb] Handle STT_TLS symbol type in ELF parser #178975)

Deprecation/Removal

• Remove mips64 support [lldb] Remove mips64 support for FreeBSD #179582, [lldb][Process] Remove mips64 POSIX support #179987
• Assume minimum FreeBSD version is 14 [lldb] [Process/FreeBSD] Assume minimum is FreeBSD 14 #179587

Misc

• Reflect FreeBSD Git migration in comments [lldb] [Process/Utility] Update code url for FreeBSD in comments #178556

Kernel Debugging

Architecture support

• arm
• ppc
• ppc64
• ppc64le
• riscv64

Debugger

• Print kernel message buffer [lldb][Process/FreeBSDKernel] Print unread message buffer on start #178027
• Automatically select crashed thread [lldb] [Process/FreeBSDKernel] Select paniced thread automatically #178069
• Order thread list incrementally by pid [lldb] [Process/FreeBSDKernel] List threads in correct order #178306
• Print loaded debugging symbols from kenrel modules
• Enable writing to /dev/mem

Testing

• Current Process/FreeBSDKernel testing suite is a few years old and it depends on quirks like patching LLDB codebase which makes testing harder. The goal is to reconstruct a comprehensive testing suite for Process/FreeBSDKernel plugin.

Misc

• Add FreeBSD kernel debugging support in documentation [lldb][docs] Add FreeBSD kernel debugging information #179597

[mchoo7]

@emaste @DavidSpickett @aokblast

I have a few words on testing kernel debugging:

Frankly speaking, I don't see the benefit of keeping libfbsdvmcore. Although it sounds great that one can analyze core dump across different operating systems, this doesn't happen often in reality. For example, I've never seen any case analyzing Linux kernel dump on macOS or FreeBSD or analyzing FreeBSD core dump on Linux or macOS, etc. It also introduces hacks such as patching third-party library for testing, making people hesitate from actively testing these.

I will implement DoMemoryWrite() for kvm anyways, then the only function left for patching is DoUpdateThreadList(), but I believe this is less trivial or in worst case we can introduce settings option for testing.

I wonder if keeping libfbsdvmcore would benefit anyone and if the cost of maintenance surpasses the benefit.

[DavidSpickett]

FYI @mgorny who did this work.

It's up to FreeBSD developers to make this decision based on your usage.

Generally LLDB is a cross-debugger. So if it is practical, we allow debugging of anything from anything. However, there are times we have not done that. For instance the default PDB handler was until recently a library only available on Windows. And I've never tried it, but I'd bet 32-bit to 64-bit and big endian to little endian also have problems.

In other words: there is a line we draw where the implementation is too inconvenient, and the user base too small.

[DavidSpickett]

I will implement DoMemoryWrite() for kvm anyways, then the only function left for patching is DoUpdateThreadList(), but I believe this is less trivial or in worst case we can introduce settings option for testing.

FreeBSD developers: would options to filter the thread list have use beyond generating tests? Maybe this can become a feature rather than a hack.

(assuming this is a thing inside of lldb that is)