From 239d553dba29521cde2f882912f949c815306ab6 Mon Sep 17 00:00:00 2001
From: Stephen Barber <smbarber@chromium.org>
Date: Wed, 8 Apr 2020 19:50:34 -0700
Subject: [PATCH 2/2] amd64: replace array with inline asm

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

---
 amd64.c | 93 ++++++++++++++++++++++++++-------------------------------
 1 file changed, 43 insertions(+), 50 deletions(-)

diff --git a/amd64.c b/amd64.c
index ab62bd9..0a93e30 100755
--- a/amd64.c
+++ b/amd64.c
@@ -13,12 +13,12 @@ static thread_local long long co_active_buffer[64];
 static thread_local cothread_t co_active_handle = 0;
 static void (*co_swap)(cothread_t, cothread_t) = 0;
 
+#ifdef _WIN32
 #ifdef LIBCO_MPROTECT
   alignas(4096)
 #else
   section(text)
 #endif
-#ifdef _WIN32
   /* ABI: Win64 */
   static const unsigned char co_swap_function[4096] = {
     0x48, 0x89, 0x22,              /* mov [rdx],rsp          */
@@ -78,37 +78,39 @@ static void (*co_swap)(cothread_t, cothread_t) = 0;
     #endif
   }
 #else
-  /* ABI: SystemV */
-  static const unsigned char co_swap_function[4096] = {
-    0x48, 0x89, 0x26,        /* mov [rsi],rsp    */
-    0x48, 0x8b, 0x27,        /* mov rsp,[rdi]    */
-    0x58,                    /* pop rax          */
-    0x48, 0x89, 0x6e, 0x08,  /* mov [rsi+ 8],rbp */
-    0x48, 0x89, 0x5e, 0x10,  /* mov [rsi+16],rbx */
-    0x4c, 0x89, 0x66, 0x18,  /* mov [rsi+24],r12 */
-    0x4c, 0x89, 0x6e, 0x20,  /* mov [rsi+32],r13 */
-    0x4c, 0x89, 0x76, 0x28,  /* mov [rsi+40],r14 */
-    0x4c, 0x89, 0x7e, 0x30,  /* mov [rsi+48],r15 */
-    0x48, 0x8b, 0x6f, 0x08,  /* mov rbp,[rdi+ 8] */
-    0x48, 0x8b, 0x5f, 0x10,  /* mov rbx,[rdi+16] */
-    0x4c, 0x8b, 0x67, 0x18,  /* mov r12,[rdi+24] */
-    0x4c, 0x8b, 0x6f, 0x20,  /* mov r13,[rdi+32] */
-    0x4c, 0x8b, 0x77, 0x28,  /* mov r14,[rdi+40] */
-    0x4c, 0x8b, 0x7f, 0x30,  /* mov r15,[rdi+48] */
-    0xff, 0xe0,              /* jmp rax          */
-  };
 
+  void co_swap_function(cothread_t, cothread_t);
+
+  __asm__(
+    ".text\n"
+    ".align 4\n"
+    ".type co_swap_function @function\n"
+    ".intel_syntax noprefix\n"
+    "co_swap_function:\n"
+
+    "mov [rsi],rsp\n"
+    "mov rsp,[rdi]\n"
+    "pop rax\n"
+    "mov [rsi+ 8],rbp\n"
+    "mov [rsi+16],rbx\n"
+    "mov [rsi+24],r12\n"
+    "mov [rsi+32],r13\n"
+    "mov [rsi+40],r14\n"
+    "mov [rsi+48],r15\n"
+    "mov rbp,[rdi+ 8]\n"
+    "mov rbx,[rdi+16]\n"
+    "mov r12,[rdi+24]\n"
+    "mov r13,[rdi+32]\n"
+    "mov r14,[rdi+40]\n"
+    "mov r15,[rdi+48]\n"
+    "jmp rax\n"
+
+    ".size co_swap_function, .-co_swap_function\n"
+    ".att_syntax\n"
+  );
   #include <unistd.h>
-  #include <sys/mman.h>
 
-  static void co_init() {
-    #ifdef LIBCO_MPROTECT
-    unsigned long long addr = (unsigned long long)co_swap_function;
-    unsigned long long base = addr - (addr % sysconf(_SC_PAGESIZE));
-    unsigned long long size = (addr - base) + sizeof co_swap_function;
-    mprotect((void*)base, size, PROT_READ | PROT_EXEC);
-    #endif
-  }
+  static void co_init() {}
 #endif
 
 static void crash() {
@@ -129,33 +131,20 @@ cothread_t co_derive(void* memory, unsigned int size, void (*entrypoint)(void))
   if(!co_active_handle) co_active_handle = &co_active_buffer;
 
   if(handle = (cothread_t)memory) {
-    long long *p = (long long*)((char*)handle + size);  /* seek to top of stack */
-    *--p = (long long)crash;                            /* crash if entrypoint returns */
-    *--p = (long long)entrypoint;                       /* start of function */
-    *(long long*)handle = (long long)p;                 /* stack pointer */
+    unsigned int offset = (size & ~15) - 32;
+    long long *p = (long long*)((char*)handle + offset);  /* seek to top of stack */
+    *--p = (long long)crash;                              /* crash if entrypoint returns */
+    *--p = (long long)entrypoint;                         /* start of function */
+    *(long long*)handle = (long long)p;                   /* stack pointer */
   }
 
   return handle;
 }
 
 cothread_t co_create(unsigned int size, void (*entrypoint)(void)) {
-  cothread_t 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 += 512;  /* allocate additional space for storage */
-  size &= ~15;  /* align stack to 16-byte boundary */
-
-  if(handle = (cothread_t)malloc(size)) {
-    long long *p = (long long*)((char*)handle + size);  /* seek to top of stack */
-    *--p = (long long)crash;                            /* crash if entrypoint returns */
-    *--p = (long long)entrypoint;                       /* start of function */
-    *(long long*)handle = (long long)p;                 /* stack pointer */
-  }
-
-  return handle;
+  void* memory = malloc(size);
+  if(!memory) return (cothread_t)0;
+  return co_derive(memory, size, entrypoint);
 }
 
 void co_delete(cothread_t handle) {
@@ -167,6 +156,10 @@ 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