[Lldb-commits] [PATCH] D121935: added intel-pt build instructions for lldb

[Alisamar Husain via Phabricator via lldb-commits]

zrthxn created this revision.
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Herald added a project: LLDB.
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Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D121935

Files:
  lldb/source/Plugins/Trace/intel-pt/README.md


Index: lldb/source/Plugins/Trace/intel-pt/README.md
===================================================================
--- /dev/null
+++ lldb/source/Plugins/Trace/intel-pt/README.md
@@ -0,0 +1,90 @@
+## Instructions to build LLDB with Intel® PT Support
+
+### Before you get started
+
+1. Confirm that your processor is an Intel® x86_64 based processor.
+
+2. Check for the existance of this particular file on your Linux system
+    ```bash
+    cat /sys/bus/event_source/devices/intel_pt/type
+    ```
+    The output of this should be a number greater than ...?
+
+### Build Instructions
+
+1. Clone [LibIPT library](https://github.com/intel/libipt). The Intel® Processor Trace Decoder Library is Intel's® reference implementation for decoding Intel® PT. 
+    ```bash
+    git clone git at github.com:intel/libipt.git
+    ```
+
+2. Clone [the LLVM Project](https://github.com/llvm/llvm-project) in its entirety from Github or Phabricator.
+    ```bash
+    git clone git at github.com:llvm/llvm-project.git
+    ```
+
+3. Create build directories for both of these projects, outside the repositories.
+    ```bash
+    mkdir lldb-build libipt-build
+    ```
+
+4. Start by building the libipt library first. LibIPT uses CMake and Make so *make* sure you have those. From here we will use `<lldb-build>` and `<libipt-build>` to represent the full paths of these directories. Change this in the following commands to the full path for your system.
+    ```bash
+    cmake -S libipt -B <libipt-build>
+    ```
+    Run make in the LibIPT build directory
+    ```bash
+    cd <libipt-build>
+    make
+    cd ..
+    ```
+    This will generate a few files in the `<libipt-build>/lib` and `<libipt-build>/libipt/include` directories.
+
+5. Now it is time to build LLDB and link the LibIPT build and header files into it. Start by configuring all the build files for LLDB from LLVM.
+    ```bash
+    cmake \                
+      -B lldb-build \
+      -G Ninja \
+            -DLLVM_ENABLE_PROJECTS="clang;libcxx;lldb;libcxxabi" \
+            -DLLDB_BUILD_INTEL_PT=ON \
+            -DLIBIPT_INCLUDE_PATH="<libipt-build>/libipt/include" \
+            -DLIBIPT_LIBRARY_PATH="<libipt-build>/lib" \
+      -S llvm-project/llvm
+    ```
+    If this step goes right, you should see no errors and **no warnings for unused variables.**
+    We have now configured the LLDB build to be built with Ninja. Make sure you have `ninja` installed.
+
+6. Build LLDB. This will take a while.
+    ```bash
+    cd <lldb-build>
+    ninja lldb lldb-server
+    ```
+
+7. When the build completes after a few decades, test it by running the version you just built.
+    ```bash
+    ./bin/lldb <program>
+    ```
+    Inside LLDB, set a breakpoint and start the process runnning
+    ```lldb
+    (lldb) break main
+    (lldb) run
+    ```
+    Now, if everything went well, when you run the following command, you should see no errors.
+    ```lldb
+    (lldb) process trace start
+    ```
+    You should also be able to see the instructions for any line.
+    ```lldb
+    (lldb) next
+    (lldb) thread trace dump instructions
+    ```
+
+Congratulations, you can now trace away!
+
+### References
+
+Some details about how Intel® Processor Trace works are in [this great blog post](https://engineering.fb.com/2021/04/27/developer-tools/reverse-debugging/).
+Other things about how LLDB works with this are included in [the RFC document](https://docs.google.com/document/d/1cOVTGp1sL_HBXjP9eB7qjVtDNr5xnuZvUUtv43G5eVI/edit#) for this.
+
+- https://easyperf.net/blog/2019/08/23/Intel-Processor-Trace
+- https://easyperf.net/blog/2019/08/30/Intel-PT-part2#appendix-how-to-build-gdb-with-intel-pt-support
+- https://reviews.llvm.org/D91679
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