From 5141044c0620a2e9b9bd4d0aa60ac2de7049764e Mon Sep 17 00:00:00 2001
From: Mathieu Maret <mathieu.maret@gmail.com>
Date: Wed, 22 Apr 2020 17:31:37 +0200
Subject: [PATCH] use popal/pushal for context switch

Should take fewer clock nd save esp
---
 core/cpu_context.c        |  5 +++--
 core/cpu_context_switch.S | 42 +++++++++++----------------------------
 2 files changed, 15 insertions(+), 32 deletions(-)

diff --git a/core/cpu_context.c b/core/cpu_context.c
index dcba68b..c4f376c 100644
--- a/core/cpu_context.c
+++ b/core/cpu_context.c
@@ -36,12 +36,13 @@ struct cpu_state {
                  thread, even for a user thread */
   uint16_t alignment_padding; /* unused */
   uint32_t eax;
-  uint32_t ebx;
   uint32_t ecx;
   uint32_t edx;
+  uint32_t ebx;
+  uint32_t ebp;
+  uint32_t esp;
   uint32_t esi;
   uint32_t edi;
-  uint32_t ebp;
 
   /* MUST NEVER CHANGE (dependent on the IA32 iret instruction) */
   uint32_t error_code;
diff --git a/core/cpu_context_switch.S b/core/cpu_context_switch.S
index ccfa146..aa7e5f5 100644
--- a/core/cpu_context_switch.S
+++ b/core/cpu_context_switch.S
@@ -6,20 +6,14 @@
 .globl cpu_context_switch
 .type cpu_context_switch, @function
 cpu_context_switch:
-        // arg2= to_context    --    esp+64
-        // arg1= from_context  --    esp+60
-        // caller ip           --    esp+56
-  pushf              // (eflags)     esp+52
-  pushl %cs          // (cs)         esp+48
-  pushl $resume_pc   // (ip)         esp+44
-  pushl $0           // (error code) esp+40
-  pushl %ebp         //              esp+36
-  pushl %edi         //              esp+32
-  pushl %esi         //              esp+28
-  pushl %edx         //              esp+24
-  pushl %ecx         //              esp+20
-  pushl %ebx         //              esp+16
-  pushl %eax         //              esp+12
+        // arg2= to_context    --    esp+68
+        // arg1= from_context  --    esp+64
+        // caller ip           --    esp+60
+  pushf              // (eflags)     esp+56
+  pushl %cs          // (cs)         esp+52
+  pushl $resume_pc   // (ip)         esp+48
+  pushl $0           // (error code) esp+44
+  pushal              // (general reg) esp+12+8*4
   subl $2, %esp      // (alignment)  esp+10
   pushw %ss          //              esp+8
   pushw %ds          //              esp+6
@@ -32,11 +26,11 @@ cpu_context_switch:
    */
 
   /* Store the address of the saved context */
-  movl  60(%esp), %ebx
+  movl  64(%esp), %ebx
   movl  %esp, (%ebx)
 
   /* This is the proper context switch ! We change the stack here */
-  movl 64(%esp), %esp
+  movl 68(%esp), %esp
 
   /* Restore the CPU context */
   popw %gs
@@ -45,13 +39,7 @@ cpu_context_switch:
   popw %ds
   popw %ss
   addl $2,%esp
-  popl %eax
-  popl %ebx
-  popl %ecx
-  popl %edx
-  popl %esi
-  popl %edi
-  popl %ebp
+  popal
   addl $4, %esp /* Ignore "error code" */
 
   /* This restores the eflags, the cs and the eip registers */
@@ -94,13 +82,7 @@ cpu_context_exit_to:
   popw %ds
   popw %ss
   addl $2,%esp
-  popl %eax
-  popl %ebx
-  popl %ecx
-  popl %edx
-  popl %esi
-  popl %edi
-  popl %ebp
+  popal
   addl $4, %esp /* Ignore "error code" */
 
   /* This restores the eflags, the cs and the eip registers */