From 9b2906f9ff440d9b7c31479f9c9629b5aa47cc5a Mon Sep 17 00:00:00 2001
From: Rain Mark <rain.by.zhou@gmail.com>
Date: Thu, 27 Jan 2022 04:32:38 -0500
Subject: [PATCH] add split stack

---
 build.sh                          |  4 +++
 coroutine.cpp                     |  6 ++++
 coroutine.h                       | 54 +++++++++++++++++++++++++++++++
 gcc-split-stack-extra-space.patch | 26 +++++++++++++++
 splitstack.cpp                    | 14 ++++++++
 5 files changed, 104 insertions(+)
 create mode 100644 gcc-split-stack-extra-space.patch
 create mode 100644 splitstack.cpp

diff --git a/build.sh b/build.sh
index 29949bb..ace1117 100755
--- a/build.sh
+++ b/build.sh
@@ -12,3 +12,7 @@ $CXX $FLAGS future_test.cpp -o bin/future_test
 $CXX $FLAGS -O0 loop_test.cpp coroutine.cpp *.S -o bin/loop_test
 
 $CXX $FLAGS -O0 httpd/httpd.cpp coroutine.cpp *.S -o bin/httpd
+
+$CXX $FLAGS -fsplit-stack -O0 splitstack.cpp -o bin/splitstack
+
+$CXX $FLAGS -fsplit-stack -DSPLIT_STACK loop_test.cpp coroutine.cpp *.S -o bin/loop_split_stack_test
diff --git a/coroutine.cpp b/coroutine.cpp
index 06ff4c2..e0e2e1e 100644
--- a/coroutine.cpp
+++ b/coroutine.cpp
@@ -15,6 +15,9 @@ void main(coro_t* coro, context from) {
 
 void coro_t::switch_out() {
   current = next_;
+#ifdef SPLIT_STACK
+  switch_split_stack_context(stack_.ss_ctx_, stack_.next_);
+#endif
   context from = switch_context(next_, next_->ctx_);
   next_ = static_cast<coro_t*>(from);
   next_->ctx_ = from;
@@ -23,6 +26,9 @@ void coro_t::switch_out() {
 void coro_t::switch_in() {
   next_ = current;
   current = this;
+#ifdef SPLIT_STACK
+  switch_split_stack_context(stack_.next_, stack_.ss_ctx_);
+#endif
   ctx_ = switch_context(this, ctx_);
 }
 
diff --git a/coroutine.h b/coroutine.h
index 5cff059..fdd8555 100644
--- a/coroutine.h
+++ b/coroutine.h
@@ -6,6 +6,36 @@
 
 #include <future.h>
 
+#ifdef SPLIT_STACK
+
+///////////////////////////
+// forward declaration for splitstack-functions defined in libgcc
+// https://github.com/gcc-mirror/gcc/blob/master/libgcc/generic-morestack.c
+// https://github.com/gcc-mirror/gcc/blob/master/libgcc/config/i386/morestack.S
+
+enum splitstack_context_offsets {
+  MORESTACK_SEGMENTS = 0,
+  CURRENT_SEGMENT = 1,
+  CURRENT_STACK = 2,
+  STACK_GUARD = 3,
+  INITIAL_SP = 4,
+  INITIAL_SP_LEN = 5,
+  BLOCK_SIGNALS = 6,
+
+  NUMBER_OFFSETS = 10
+};
+
+extern "C" {
+  void *__splitstack_makecontext(std::size_t, void* [NUMBER_OFFSETS], std::size_t*);
+  void __splitstack_setcontext(void* [NUMBER_OFFSETS]);
+  void __splitstack_getcontext(void* [NUMBER_OFFSETS]);
+  void __splitstack_releasecontext(void* [NUMBER_OFFSETS]);
+  void __splitstack_resetcontext(void* [NUMBER_OFFSETS]);
+  void __splitstack_block_signals_context(void* [NUMBER_OFFSETS], int* new_value, int* old_value);
+}
+
+#endif
+
 namespace cops {
 class coro_t;
 class event_loop_t;
@@ -23,10 +53,20 @@ namespace cops {
 class stack_t {
 public:
   stack_t(size_t size = 64 * 1024) : size_(size) {
+#ifdef SPLIT_STACK
+    sp_ = static_cast<char*>(__splitstack_makecontext(size_, ss_ctx_, &size_));
+    static int off = 0;
+    __splitstack_block_signals_context(ss_ctx_, &off, 0);
+#else
     sp_ = new char[size_];
+#endif
   }
   ~stack_t() {
+#ifdef SPLIT_STACK
+    __splitstack_releasecontext(ss_ctx_);
+#else
     delete[] sp_;
+#endif
   }
 
   void* sp() {
@@ -36,8 +76,22 @@ public:
 private:
   char* sp_;
   size_t size_;
+#ifdef SPLIT_STACK
+public:
+  using split_stack_context = void* [NUMBER_OFFSETS];
+  split_stack_context ss_ctx_{0};
+  split_stack_context next_{0};
+#endif
 };
 
+#ifdef SPLIT_STACK
+inline void switch_split_stack_context(stack_t::split_stack_context from,
+                                       stack_t::split_stack_context to) {
+  __splitstack_getcontext(from);
+  __splitstack_setcontext(to);
+}
+#endif
+
 class coro_t {
 public:
   using Fn = std::function<void(void)>;
diff --git a/gcc-split-stack-extra-space.patch b/gcc-split-stack-extra-space.patch
new file mode 100644
index 0000000..123155f
--- /dev/null
+++ b/gcc-split-stack-extra-space.patch
@@ -0,0 +1,26 @@
+diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
+index 59101d8..4cbad01 100644
+--- a/gcc/config/i386/i386.c
++++ b/gcc/config/i386/i386.c
+@@ -9488,7 +9488,7 @@ ix86_expand_split_stack_prologue (void)
+ 
+   ix86_finalize_stack_frame_flags ();
+   struct ix86_frame &frame = cfun->machine->frame;
+-  allocate = frame.stack_pointer_offset - INCOMING_FRAME_SP_OFFSET;
++  allocate = frame.stack_pointer_offset - INCOMING_FRAME_SP_OFFSET + 64 * 1024;
+ 
+   /* This is the label we will branch to if we have enough stack
+      space.  We expect the basic block reordering pass to reverse this
+diff --git a/libgcc/config/i386/morestack.S b/libgcc/config/i386/morestack.S
+index 519bbbc..0f0a79e 100644
+--- a/libgcc/config/i386/morestack.S
++++ b/libgcc/config/i386/morestack.S
+@@ -84,7 +84,7 @@
+ 
+ 
+ # The amount of space we ask for when calling non-split-stack code.
+-#define NON_SPLIT_STACK 0x100000
++#define NON_SPLIT_STACK 0x8000
+ 
+ # This entry point is for split-stack code which calls non-split-stack
+ # code.  When the linker sees this case, it converts the call to
diff --git a/splitstack.cpp b/splitstack.cpp
new file mode 100644
index 0000000..bd09163
--- /dev/null
+++ b/splitstack.cpp
@@ -0,0 +1,14 @@
+#include <stdio.h>
+
+int foo(int x1) {
+    printf("%d\n", x1);
+    return 0;
+}
+
+int bar(int x2) {
+    return foo(x2);
+}
+
+int main() {
+    return bar(0);
+}