[LLDB][LoongArch] Fix build errors about NT_LOONGARCH_HW_{BREAK,WATCH}

[seehearfeel]

On some OS distros such as LoongArch Fedora 38 mate-5 [1], there are
no macro definitions NT_LOONGARCH_HW_BREAK and NT_LOONGARCH_HW_WATCH
in the system header, then there exist some errors when building LLDB
on LoongArch.

(1) Description of Problem:

llvm-project/lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_loongarch64.cpp:529:16:
error: 'NT_LOONGARCH_HW_WATCH' was not declared in this scope; did you mean 'NT_LOONGARCH_LBT'?
  529 |   int regset = NT_LOONGARCH_HW_WATCH;
      |                ^~~~~~~~~~~~~~~~~~~~~
      |                NT_LOONGARCH_LBT
llvm-project/lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_loongarch64.cpp:543:12:
error: 'NT_LOONGARCH_HW_BREAK' was not declared in this scope; did you mean 'NT_LOONGARCH_CSR'?
  543 |   regset = NT_LOONGARCH_HW_BREAK;
      |            ^~~~~~~~~~~~~~~~~~~~~
      |            NT_LOONGARCH_CSR

(2) Steps to Reproduce:

git clone https://github.com/llvm/llvm-project.git
mkdir -p llvm-project/llvm/build && cd llvm-project/llvm/build
cmake .. -G "Ninja" \
         -DCMAKE_BUILD_TYPE=Release \
         -DLLVM_BUILD_RUNTIME=OFF \
         -DLLVM_ENABLE_PROJECTS="clang;lldb" \
         -DCMAKE_INSTALL_PREFIX=/usr/local/llvm \
         -DLLVM_TARGETS_TO_BUILD="LoongArch" \
         -DLLVM_HOST_TRIPLE=loongarch64-redhat-linux
ninja

(3) Additional Info:

Maybe there are no problems on the OS distros with newer glibc devel
library, so this issue is related with OS distros.

(4) Root Cause Analysis:

This is because the related Linux kernel commit [2] was merged in
2023-02-25 and the glibc devel library has some delay with kernel,
the glibc version of specified OS distros is not updated in time.

(5) Final Solution:

One way is to ask the maintainer of OS distros to update glibc devel
library, but it is better to not depend on the glibc version.

In order to avoid the build errors, just define NT_LOONGARCH_HW_BREAK
and NT_LOONGARCH_HW_WATCH in LLDB if there are no these definitions in
the system header.

By the way, in order to fit within 80 columns, use C++-style comments
for the new added NT_LOONGARCH_HW_BREAK and NT_LOONGARCH_HW_WATCH.

While at it, for consistency, just modify the current NT_LOONGARCH_LSX
and NT_LOONGARCH_LASX to C++-style comments too.

[1] https://mirrors.wsyu.edu.cn/fedora/linux/development/rawhide/Everything/loongarch64/iso/livecd-fedora-mate-5.loongarch64.iso
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1a69f7a161a7

Signed-off-by: Tiezhu Yang <[email protected]>

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[llvmbot]

@llvm/pr-subscribers-lldb

Author: None (seehearfeel)

Changes

1. [LLDB][LoongArch] Fix build errors about NT_LOONGARCH_HW_{BREAK,WATCH}
2. [LLDB][LoongArch] Extend the maximum number of watchpoints

---

Full diff: https://github.com/llvm/llvm-project/pull/126020.diff

1 Files Affected:

• (modified) lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_loongarch64.cpp (+22-2)

diff --git a/lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_loongarch64.cpp b/lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_loongarch64.cpp
index b04018ee243fd7d..8eb2cb65c76d2ea 100644
--- a/lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_loongarch64.cpp
+++ b/lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_loongarch64.cpp
@@ -36,9 +36,29 @@
   0xa03 /* LoongArch Advanced SIMD eXtension registers */
 #endif
 
+#ifndef NT_LOONGARCH_HW_BREAK
+#define NT_LOONGARCH_HW_BREAK	0xa05   /* LoongArch hardware breakpoint registers */
+#endif
+
+#ifndef NT_LOONGARCH_HW_WATCH
+#define NT_LOONGARCH_HW_WATCH	0xa06   /* LoongArch hardware watchpoint registers */
+#endif
+
 #define REG_CONTEXT_SIZE                                                       \
   (GetGPRSize() + GetFPRSize() + sizeof(m_lsx) + sizeof(m_lasx))
 
+#ifndef user_watch_state_v2
+struct user_watch_state_v2 {
+	uint64_t dbg_info;
+	struct {
+		uint64_t    addr;
+		uint64_t    mask;
+		uint32_t    ctrl;
+		uint32_t    pad;
+	} dbg_regs[14];
+};
+#endif
+
 using namespace lldb;
 using namespace lldb_private;
 using namespace lldb_private::process_linux;
@@ -528,7 +548,7 @@ llvm::Error NativeRegisterContextLinux_loongarch64::ReadHardwareDebugInfo() {
 
   int regset = NT_LOONGARCH_HW_WATCH;
   struct iovec ioVec;
-  struct user_watch_state dreg_state;
+  struct user_watch_state_v2 dreg_state;
   Status error;
 
   ioVec.iov_base = &dreg_state;
@@ -556,7 +576,7 @@ llvm::Error NativeRegisterContextLinux_loongarch64::ReadHardwareDebugInfo() {
 llvm::Error NativeRegisterContextLinux_loongarch64::WriteHardwareDebugRegs(
     DREGType hwbType) {
   struct iovec ioVec;
-  struct user_watch_state dreg_state;
+  struct user_watch_state_v2 dreg_state;
   int regset;
 
   memset(&dreg_state, 0, sizeof(dreg_state));

[wangleiat]

LGTM, execpt for the comment style.

[wangleiat]

https://llvm.org/docs/CodingStandards.html#comment-formatting
In general, prefer C++-style comments // .

[SixWeining]

LGTM with a nit.

LLVM uses squash merge. If you'd to keep the 2 commits, please summit 2 PRs.

[SixWeining]

Seems the code indent is inappropriate.

[DavidSpickett]

I see that the basics of this were added 2 years ago - torvalds/linux@1a69f7a.

So I assume the build error here is not that NT_LOONGARCH_HW_BREAK is not defined, it's that user_watch_state got redefined?

Please explain all this in the PR description. GitHub does not use the contents of the commit messages for the final commit. Link to kernel commits as well, that will be easier than writing out the same justifications again.

Also include something in the title so it's like "Fix build errors with user_watch_v2". If you need to find this commit again, that will help you a lot.

I'd like to know what your intent is with supporting older kernels, if at all. Given that this new structure is not the same size as the other one, or is it? A pad was added but perhaps that just made the existing compiler padding explicit?

(I don't care if you do support older kernels or not, but let's get the intent documented)

[DavidSpickett]

This comment needs to give more context, explain what came before, which one lldb uses and the consequences of that re. support for older kernels or not.

[DavidSpickett]

So I assume the build error here is not that NT_LOONGARCH_HW_BREAK is not defined, it's that user_watch_state got redefined?

And if so, why are you adding a redefinition of it?

This would only help if you are building lldb against kernel headers from before a time where the kernel had hardware watchpoint support. Which could be a valid use case, I'm not sure. But is that in fact the use case here?

[seehearfeel]

I see that the basics of this were added 2 years ago - torvalds/linux@1a69f7a.

So I assume the build error here is not that NT_LOONGARCH_HW_BREAK is not defined, it's that user_watch_state got redefined?

Actually, as the commit message said, it is because NT_LOONGARCH_HW_{BREAK,WATCH} are not defined in the system header.

Please explain all this in the PR description. GitHub does not use the contents of the commit messages for the final commit. Link to kernel commits as well, that will be easier than writing out the same justifications again.

Also include something in the title so it's like "Fix build errors with user_watch_v2". If you need to find this commit again, that will help you a lot.

I'd like to know what your intent is with supporting older kernels, if at all. Given that this new structure is not the same size as the other one, or is it? A pad was added but perhaps that just made the existing compiler padding explicit?

(I don't care if you do support older kernels or not, but let's get the intent documented)

This PR only has one patch now, the PR title is same with the patch title.
There will be another patch to do what you said once this PR is merged.

[DavidSpickett]

Thanks! New description is very clear. Fedora 38 is a 2023 release so I can understand why there'd be folks still using it.

I assume you're going to deal with the change in struct definition in a new PR?

[DavidSpickett]

There will be another patch to do what you said once this PR is merged.

Which answers my question, sounds good to me.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[seehearfeel]

By now, the format of pr and patch seem no problems, but my email setting of GitHub is not correct, I will update the comment
once it is OK, please wait some time before merging it, thank you.

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