From 031cd302dd4c0c019101dffd8c551e97303a2b3f Mon Sep 17 00:00:00 2001
From: Benjamin Doherty <bendoherty@google.com>
Date: Mon, 30 Oct 2023 14:42:24 -0700
Subject: [PATCH] Capture command callstacks for debugging

---
 .../include/private/backend/CommandStream.h   | 20 +++++++++++++++++++
 .../backend/include/private/backend/Driver.h  |  3 +++
 libs/utils/include/utils/CallStack.h          | 13 ++++++++----
 libs/utils/src/CallStack.cpp                  |  4 ++--
 4 files changed, 34 insertions(+), 6 deletions(-)

diff --git a/filament/backend/include/private/backend/CommandStream.h b/filament/backend/include/private/backend/CommandStream.h
index 1901361542..92c1f7a4be 100644
--- a/filament/backend/include/private/backend/CommandStream.h
+++ b/filament/backend/include/private/backend/CommandStream.h
@@ -73,14 +73,32 @@ public:
         // a cost here (writing and reading the stack at each iteration), in the end it's
         // probably better to pay the cost at just one location.
         intptr_t next;
+        driver.mCurrentExecutingCommand = this;
         mExecute(driver, this, &next);
         return reinterpret_cast<CommandBase*>(reinterpret_cast<intptr_t>(this) + next);
     }
 
+    inline void captureCallstack() noexcept {
+        auto c = utils::CallStack::unwind(4);
+        size_t i = 0;
+        for (; i < c.getFrameCount() && i < 16; i++) {
+            mCallstack[i] = c[i];
+        }
+        for (; i < 16; i++) {
+            mCallstack[i] = 0;
+        }
+    }
+
+    void printCallstack() noexcept {
+        auto c = utils::CallStack(mCallstack);
+        utils::slog.d << c << utils::io::endl;
+    }
+
     inline ~CommandBase() noexcept = default;
 
 private:
     Execute mExecute;
+    std::array<intptr_t, 16> mCallstack = {0};
 };
 
 // ------------------------------------------------------------------------------------------------
@@ -218,6 +236,7 @@ public:
         using Cmd = COMMAND_TYPE(methodName);                                                   \
         void* const p = allocateCommand(CommandBase::align(sizeof(Cmd)));                       \
         new(p) Cmd(mDispatcher.methodName##_, APPLY(std::move, params));                        \
+        ((Cmd*)p)->captureCallstack();                                                          \
         DEBUG_COMMAND_END(methodName, false);                                                   \
     }
 
@@ -237,6 +256,7 @@ public:
         using Cmd = COMMAND_TYPE(methodName##R);                                                \
         void* const p = allocateCommand(CommandBase::align(sizeof(Cmd)));                       \
         new(p) Cmd(mDispatcher.methodName##_, RetType(result), APPLY(std::move, params));       \
+        ((Cmd*)p)->captureCallstack();                                                          \
         DEBUG_COMMAND_END(methodName, false);                                                   \
         return result;                                                                          \
     }
diff --git a/filament/backend/include/private/backend/Driver.h b/filament/backend/include/private/backend/Driver.h
index a8c31ef4bf..36fcf3102a 100644
--- a/filament/backend/include/private/backend/Driver.h
+++ b/filament/backend/include/private/backend/Driver.h
@@ -53,6 +53,7 @@ template<typename T>
 class ConcreteDispatcher;
 class Dispatcher;
 class CommandStream;
+class CommandBase;
 
 class Driver {
 public:
@@ -83,6 +84,8 @@ public:
     virtual void debugCommandEnd(CommandStream* cmds,
             bool synchronous, const char* methodName) noexcept = 0;
 
+    CommandBase* mCurrentExecutingCommand = nullptr;
+
     /*
      * Asynchronous calls here only to provide a type to CommandStream. They must be non-virtual
      * so that calling the concrete implementation won't go through a vtable.
diff --git a/libs/utils/include/utils/CallStack.h b/libs/utils/include/utils/CallStack.h
index 291a748ce4..56ef41cf5d 100644
--- a/libs/utils/include/utils/CallStack.h
+++ b/libs/utils/include/utils/CallStack.h
@@ -36,6 +36,13 @@ public:
      * @see CallStack::capture()
      */
     CallStack() = default;
+    template <unsigned long N>
+    explicit CallStack(const std::array<intptr_t, N>& symbols)
+        : m_frame_count(N) {
+        for (size_t i = 0; i < N; i++) {
+            m_stack[i] = symbols[i];
+        }
+    }
     CallStack(const CallStack&) = default;
     ~CallStack() = default;
 
@@ -114,12 +121,10 @@ private:
 
     static constexpr size_t NUM_FRAMES = 20;
 
-    struct StackFrameInfo {
-        intptr_t pc;
-    };
+    using StackFrameInfo = intptr_t;
 
     size_t m_frame_count = 0;
-    StackFrameInfo m_stack[NUM_FRAMES];
+    StackFrameInfo m_stack[NUM_FRAMES] = {0};
 };
 
 } // namespace utils
diff --git a/libs/utils/src/CallStack.cpp b/libs/utils/src/CallStack.cpp
index b41c18776d..c23d139d1a 100644
--- a/libs/utils/src/CallStack.cpp
+++ b/libs/utils/src/CallStack.cpp
@@ -70,7 +70,7 @@ intptr_t CallStack::operator[](size_t index) const {
 #endif
         std::abort();
     }
-    return m_stack[index].pc;
+    return m_stack[index];
 }
 
 size_t CallStack::getFrameCount() const noexcept {
@@ -91,7 +91,7 @@ void CallStack::update_gcc(size_t ignore) noexcept {
     size -= ignore;
 #endif
     for (ssize_t i = 0; i < size; i++) {
-        m_stack[i].pc = intptr_t(array[ignore + i]);
+        m_stack[i] = intptr_t(array[ignore + i]);
     }
     size--; // the last one seems to always be 0x0