[SeaBIOS] [RFC] [PATCH 1/2] Implement support for transitioning from 16 bit to 32 bit

[Kevin O'Connor]

On Mon, Nov 22, 2010 at 07:40:36PM -0500, Kevin O'Connor wrote:
> It should be possible to extend call32() to do what you need -

FYI - here's what call32 extended to pass a parameter looks like:

--- a/src/stacks.c
+++ b/src/stacks.c
@@ -37,14 +37,14 @@ static inline void lgdt(struct descloc_s *desc) {
 }
 
 // Call a 32bit SeaBIOS function from a 16bit SeaBIOS function.
-static inline int
-call32(void *func)
+static inline u32
+call32(void *func, u32 eax, u32 errret)
 {
     ASSERT16();
     u32 cr0 = getcr0();
     if (cr0 & CR0_PE)
         // Called in 16bit protected mode?!
-        return -1;
+        return errret;
 
     // Backup cmos index register and disable nmi
     u8 cmosindex = inb(PORT_CMOS_INDEX);
@@ -69,7 +69,7 @@ call32(void *func)
         "  pushl $(" __stringify(BUILD_BIOS_ADDR) " + 1f)\n"
         "  jmp transition32\n"
         "  .code32\n"
-        "1:calll *%2\n"
+        "1:calll *%3\n"
         "  pushl $2f\n"
         "  jmp transition16big\n"
 
@@ -78,9 +78,9 @@ call32(void *func)
         "2:movl %0, %%ds\n"
         "  movl %0, %%ss\n"
         "  movl %1, %%esp\n"
-        : "=&r" (bkup_ss), "=&r" (bkup_esp)
+        : "=&r" (bkup_ss), "=&r" (bkup_esp), "+a" (eax)
         : "r" (func)
-        : "eax", "ecx", "edx", "cc", "memory");
+        : "ecx", "edx", "cc", "memory");
 
     // Restore gdt and fs/gs
     lgdt(&gdt);
@@ -90,7 +90,7 @@ call32(void *func)
     // Restore cmos index register
     outb(cmosindex, PORT_CMOS_INDEX);
     inb(PORT_CMOS_DATA);
-    return 0;
+    return eax;
 }
 
 // 16bit trampoline for enabling irqs from 32bit mode.
@@ -393,5 +393,5 @@ check_preempt(void)
         || GET_FLATPTR(MainThread.next) == &MainThread)
         return;
 
-    call32(yield_preempt);
+    call32(yield_preempt, 0, 0);
 }

-Kevin