From 4bdd15e05f47164664d41602d35fd7aab504a7c6 Mon Sep 17 00:00:00 2001
From: Stephen Barber <smbarber@chromium.org>
Date: Wed, 8 Apr 2020 16:11:31 -0700
Subject: [PATCH] arm: replace co_swap_function array with inline asm

Submitted upstream as https://github.com/canonical/libco/pull/13

---
 arm.c | 65 +++++++++++++++++++++++------------------------------------
 1 file changed, 25 insertions(+), 40 deletions(-)

diff --git a/arm.c b/arm.c
index 20c9531..7e9636b 100644
--- a/arm.c
+++ b/arm.c
@@ -13,27 +13,24 @@ extern "C" {
 
 static thread_local unsigned long co_active_buffer[64];
 static thread_local cothread_t co_active_handle = 0;
-static void (*co_swap)(cothread_t, cothread_t) = 0;
+void co_swap(cothread_t, cothread_t);
 
-#ifdef LIBCO_MPROTECT
-  alignas(4096)
-#else
-  section(text)
-#endif
-static const unsigned long co_swap_function[1024] = {
-  0xe8a16ff0,  /* stmia r1!, {r4-r11,sp,lr} */
-  0xe8b0aff0,  /* ldmia r0!, {r4-r11,sp,pc} */
-  0xe12fff1e,  /* bx lr                     */
-};
+__asm__(
+  ".text\n"
+  ".align 4\n"
+  ".type co_swap #function\n"
+  ".arm\n"
+  "co_swap:\n"
+  "mov r3, sp\n"
+  "stmia r1!, {r4-r11}\n"
+  "stmia r1!, {r3, lr}\n"
+  "ldmia r0!, {r4-r11}\n"
+  "ldmia r0!, {r3, lr}\n"
+  "mov sp, r3\n"
+  "bx lr\n"
 
-static void co_init() {
-  #ifdef LIBCO_MPROTECT
-  unsigned long addr = (unsigned long)co_swap_function;
-  unsigned long base = addr - (addr % sysconf(_SC_PAGESIZE));
-  unsigned long size = (addr - base) + sizeof co_swap_function;
-  mprotect((void*)base, size, PROT_READ | PROT_EXEC);
-  #endif
-}
+  ".size co_swap, .-co_swap\n"
+);
 
 cothread_t co_active() {
   if(!co_active_handle) co_active_handle = &co_active_buffer;
@@ -42,14 +39,11 @@ cothread_t co_active() {
 
 cothread_t co_derive(void* memory, unsigned int size, void (*entrypoint)(void)) {
   unsigned long* handle;
-  if(!co_swap) {
-    co_init();
-    co_swap = (void (*)(cothread_t, cothread_t))co_swap_function;
-  }
   if(!co_active_handle) co_active_handle = &co_active_buffer;
 
   if(handle = (unsigned long*)memory) {
-    unsigned long* p = (unsigned long*)((unsigned char*)handle + size);
+    unsigned int offset = (size & ~15);
+    unsigned long* p = (unsigned long*)((unsigned char*)handle + offset);
     handle[8] = (unsigned long)p;
     handle[9] = (unsigned long)entrypoint;
   }
@@ -58,22 +52,9 @@ cothread_t co_derive(void* memory, unsigned int size, void (*entrypoint)(void))
 }
 
 cothread_t co_create(unsigned int size, void (*entrypoint)(void)) {
-  unsigned long* handle;
-  if(!co_swap) {
-    co_init();
-    co_swap = (void (*)(cothread_t, cothread_t))co_swap_function;
-  }
-  if(!co_active_handle) co_active_handle = &co_active_buffer;
-  size += 256;
-  size &= ~15;
-
-  if(handle = (unsigned long*)malloc(size)) {
-    unsigned long* p = (unsigned long*)((unsigned char*)handle + size);
-    handle[8] = (unsigned long)p;
-    handle[9] = (unsigned long)entrypoint;
-  }
-
-  return handle;
+  void* memory = malloc(size);
+  if(!memory) return (cothread_t)0;
+  return co_derive(memory, size, entrypoint);
 }
 
 void co_delete(cothread_t handle) {
@@ -85,6 +66,10 @@ void co_switch(cothread_t handle) {
   co_swap(co_active_handle = handle, co_previous_handle);
 }
 
+int co_serializable() {
+  return 1;
+}
+
 #ifdef __cplusplus
 }
 #endif
-- 
2.26.0.292.g33ef6b2f38-goog