[SeaBIOS] [PATCH 2/2] Enhance call32() to pass a parameter to called function.

[Kevin O'Connor]

Support passing a parameter to the 32bit function, as well as
returning the result of the function back to the 16bit code.

Also, make call32 available outside of stacks.c.
---
 src/stacks.c |   18 +++++++++---------
 src/util.h   |    1 +
 2 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/src/stacks.c b/src/stacks.c
index a68d37c..c77ba1f 100644
--- 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)
+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);
@@ -63,13 +63,13 @@ call32(void *func)
         "  movl %%esp, %1\n"
         "  shll $4, %0\n"
         "  addl %0, %%esp\n"
-        "  movl %%ss, %0\n"
+        "  shrl $4, %0\n"
 
         // Transition to 32bit mode, call func, return to 16bit
         "  movl $(" __stringify(BUILD_BIOS_ADDR) " + 1f), %%edx\n"
         "  jmp transition32\n"
         "  .code32\n"
-        "1:calll *%2\n"
+        "1:calll *%3\n"
         "  movl $2f, %%edx\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);
 }
diff --git a/src/util.h b/src/util.h
index 18ab814..e513e84 100644
--- a/src/util.h
+++ b/src/util.h
@@ -211,6 +211,7 @@ char *strtcpy(char *dest, const char *src, size_t len);
 int get_keystroke(int msec);
 
 // stacks.c
+u32 call32(void *func, u32 eax, u32 errret);
 inline u32 stack_hop(u32 eax, u32 edx, void *func);
 extern struct thread_info MainThread;
 struct thread_info *getCurThread(void);
-- 
1.7.3.2