From 202bae362a204a240b4a346a97f46f9b9da16b3f Mon Sep 17 00:00:00 2001
From: Paul Mathieu <paul@ponteilla.net>
Date: Thu, 25 Sep 2025 14:15:27 +0200
Subject: [PATCH] polmon: stop using es and praying

---
 polmon.cc | 46 +++++++++++++++++++---------------------------
 1 file changed, 19 insertions(+), 27 deletions(-)

diff --git a/polmon.cc b/polmon.cc
index 3f85903..7be0641 100644
--- a/polmon.cc
+++ b/polmon.cc
@@ -74,7 +74,7 @@ void puts(const char* s) {
 // arguments on the stack in reverse order
 extern "C" uint16_t Jump(uint16_t addr, int nargs);
 asm (
-        ".section .text         \n"
+        ".section .text.Jump    \n"
         "Jump:                  \n"
         "   push %bx            \n"
         "   push %si            \n"
@@ -152,30 +152,25 @@ void WriteUint16(uint16_t a) {
     WriteUint8(a & 0xff);
 }
 
-void __set_es__(uint16_t es) {
-    asm volatile (
-            "mov %0, %%es"
-            :: "r" (es)
-            : "es"
-            );
-}
-
-uint8_t __get_es_u8__(uint16_t addr) {
-    register uint16_t ad asm ("di") = addr;
-    uint8_t ret;
-    asm volatile (
-            "movb %%es:(%1), %0"
+uint8_t __get_far_u8__(uint16_t addr, uint16_t seg) {
+    register uint16_t ad asm ("si") = addr;
+    register uint16_t sg asm ("ds") = seg;
+    register uint8_t ret asm ("al");
+    asm (
+            "lodsb              \n\t"
             : "=r" (ret)
-            : "r" (ad)
+            : "r" (ad), "r" (sg)
             );
     return ret;
 }
 
-void __set_es_u8__(uint16_t addr, uint8_t val) {
+void __set_far_u8__(uint16_t addr, uint16_t seg, uint8_t val) {
     register uint16_t ad asm ("di") = addr;
-    asm volatile (
-            "movb %0, %%es:(%1)"
-            :: "ri" (val), "rmi" (ad)
+    register uint16_t sg asm ("es") = seg;
+    register uint8_t v asm ("al") = val;
+    asm (
+            "stosb      \n\t"
+            :: "r" (sg), "r" (ad), "r" (v)
             : "memory"
             );
 }
@@ -190,17 +185,17 @@ inline static void __basic__() {
     __builtin_unreachable();
 }
 
-void Dump(uint16_t addr, int count) {
+void Dump(uint16_t addr, uint16_t seg, int count) {
     for (int i = 0; i < count; i++) {
         putc(' ');
-        uint8_t d = __get_es_u8__(addr + i);
+        uint8_t d = __get_far_u8__(addr + i, seg);
         WriteUint8(d);
     }
 #if ASCIIDUMP
     putc(' ');
     putc(' ');
     for (int i = 0; i < count; i++) {
-        uint8_t d = __get_es_u8__(addr + i);
+        uint8_t d = __get_far_u8__(addr + i, seg);
         if (d > 31 && d < 127) {
             putc(d);
         } else {
@@ -216,11 +211,10 @@ void DumpHex(uint16_t addr, uint16_t seg) {
     putc('[');
     WriteUint16(seg);
     putc(':');
-    __set_es__(seg);
     WriteUint16(addr);
     putc(']');
     putc(':');
-    Dump(addr, kDumpSize);
+    Dump(addr, seg, kDumpSize);
     putc('\r');
     putc('\n');
 }
@@ -276,7 +270,6 @@ bool ParseCommand(const char* buf, uint16_t& cur_addr, uint16_t& cur_seg) {
                 nargs++;
                 ptr += 4;
             }
-            __set_es__(cur_seg);
             uint16_t ret = Jump(cur_addr, nargs);
             asm volatile (
                     "shl %0   \n\t"
@@ -306,8 +299,7 @@ bool ParseCommand(const char* buf, uint16_t& cur_addr, uint16_t& cur_seg) {
                     continue;
                 }
                 uint8_t d = ReadUint8(ptr);
-                __set_es__(cur_seg);
-                __set_es_u8__(addr, d);
+                __set_far_u8__(addr, cur_seg, d);
                 addr++;
                 ptr += 2;
             }