Add support for thunking cdecl/stdcall-style real-mode code

Add support for thunking cdecl/stdcall-style 16-bit functions which
pass parameters on the stack.  This is necessary in order to be able
to call PnPBIOS functions without using the (rather scary) PM
interface.

5 files changed, 78 insertions, 12 deletions

diff --git a/com32.inc b/com32.inc
index c4a1faa2..47f104b4 100644
--- a/com32.inc
+++ b/com32.inc
@@ -1,6 +1,6 @@
 ;; -----------------------------------------------------------------------
 ;;
-;;   Copyright 1994-2006 H. Peter Anvin - All Rights Reserved
+;;   Copyright 1994-2007 H. Peter Anvin - All Rights Reserved
 ;;
 ;;   This program is free software; you can redistribute it and/or modify
 ;;   it under the terms of the GNU General Public License as published by
@@ -164,12 +164,13 @@ com32_call_start:
 
 		; Now everything is set up for interrupts...
 
+		push dword com32_cfarcall	; Cfarcall entry point
 		push dword com32_farcall	; Farcall entry point
 		push dword (1 << 16)		; 64K bounce buffer
 		push dword (comboot_seg << 4)	; Bounce buffer address
 		push dword com32_intcall	; Intcall entry point
 		push dword command_line		; Command line pointer
-		push dword 5			; Argument count
+		push dword 6			; Argument count
 		sti				; Interrupts OK now
 		call pm_entry			; Run the program...
 		; ... on return, fall through to com32_exit ...
@@ -232,7 +233,7 @@ com32_int_rm:
 		jmp com32_enter_pm		; Go back to PM
 
 ;
-; 16-bit system call handling code
+; 16-bit intcall/farcall handling code
 ;
 com32_sys_rm:
 		pop gs
@@ -253,7 +254,18 @@ com32_sys_rm:
 		push es
 		push fs
 		push gs
-		mov ebx,com32_sys_resume
+		mov ebx,com32_syscall.resume
+		jmp com32_enter_pm
+
+;
+; 16-bit cfarcall handing code
+;
+com32_cfar_rm:
+		retf
+.return:
+		mov sp,[cs:Com32SysSP]
+		mov [cs:RealModeEAX],eax
+		mov ebx,com32_cfarcall.resume
 		jmp com32_enter_pm
 
 ;
@@ -335,7 +347,7 @@ com32_syscall:
 		; On return, the 44-byte return structure is on the
 		; real-mode stack, plus the 10 additional bytes used
 		; by the target address (see above.)
-com32_sys_resume:
+.resume:
 		movzx esi,word [word RealModeSSSP]
 		movzx eax,word [word RealModeSSSP+2]
 		mov edi,[esp+12*4]	; Dest regs
@@ -354,11 +366,53 @@ com32_sys_resume:
 		popfd
 		ret			; Return to 32-bit program
 
+;
+; Cfarcall invocation.  We copy the stack frame to the real-mode stack,
+; followed by the return CS:IP and the CS:IP of the target function.
+;
+com32_cfarcall:
+		pushfd
+		pushad
+
+		cld
+		mov ecx,[esp+12*4]		; Size of stack frame
+
+		movzx edi,word [word RealModeSSSP]
+		movzx ebx,word [word RealModeSSSP+2]
+		mov [word Com32SysSP],di
+		sub edi,ecx		; Allocate space for stack frame
+		and edi,~3		; Round
+		sub edi,4*2		; Return pointer, return value
+		mov [word RealModeSSSP],di
+		shl ebx,4
+		add edi,ebx		; Create linear address
+
+		mov eax,[esp+10*4]	; CS:IP
+		stosd			; Save to stack frame
+		mov eax,com32_cfar_rm.return	; Return seg:off
+		stosd
+		mov esi,[esp+11*4]	; Stack frame
+		mov eax,ecx		; Copy the stack frame
+		rep movsd
+		mov ecx,eax
+		and ecx,3
+		rep movsb
+
+		mov bx,com32_cfar_rm
+		jmp com32_enter_rm
+
+.resume:
+		popad
+		mov eax,[word RealModeEAX]
+		popfd
+		ret
+
 		bits 16
 
 		section .bss1
 		alignb 4
 RealModeSSSP	resd 1			; Real-mode SS:SP
+RealModeEAX	resd 1			; Real mode EAX
 PMESP		resd 1			; Protected-mode ESP
 Com32SysSP	resw 1			; SP saved during COM32 syscall
 
diff --git a/com32/include/com32.h b/com32/include/com32.h
index 264f6091..7e618977 100644
--- a/com32/include/com32.h
+++ b/com32/include/com32.h
@@ -74,14 +74,17 @@ extern struct com32_sys_args {
   void *cs_bounce;
   uint32_t cs_bounce_size;
   void __cdecl (*cs_farcall)(uint32_t, const com32sys_t *, com32sys_t *);
+  int __cdecl (*cs_cfarcall)(uint32_t, const void *, uint32_t);
 } __com32;
 
 /*
  * System call wrapper functions
  */
 void __intcall(uint8_t __i, const com32sys_t *__sr, com32sys_t *__dr);
-void __farcall(uint16_t __es, uint16_t __eo,
+void __farcall(uint16_t __cs, uint16_t __ip,
 	       const com32sys_t *__sr, com32sys_t *__dr);
+int __cfarcall(uint16_t __cs, uint16_t __ip,
+	       const void *__stack, uint32_t __stack_size);
 extern const com32sys_t __com32_zero_regs;
 
 /*
diff --git a/com32/lib/Makefile b/com32/lib/Makefile
index 991d5882..1cde067d 100644
--- a/com32/lib/Makefile
+++ b/com32/lib/Makefile
@@ -24,7 +24,7 @@ LIBOBJS = \
 	libgcc/__muldi3.o libgcc/__udivmoddi4.o libgcc/__umoddi3.o	\
 	libgcc/__divdi3.o libgcc/__moddi3.o				\
 	\
-	sys/intcall.o sys/farcall.o sys/zeroregs.o			\
+	sys/intcall.o sys/farcall.o sys/cfarcall.o sys/zeroregs.o	\
 	sys/entry.o sys/exit.o sys/argv.o sys/times.o			\
 	sys/fileinfo.o sys/opendev.o sys/read.o sys/write.o sys/ftell.o \
 	sys/close.o sys/open.o sys/fileread.o sys/fileclose.o		\
diff --git a/com32/lib/sys/entry.S b/com32/lib/sys/entry.S
index be42c8b2..c959c091 100644
--- a/com32/lib/sys/entry.S
+++ b/com32/lib/sys/entry.S
@@ -1,6 +1,6 @@
 # -----------------------------------------------------------------------
 #
-#   Copyright 2003-2004 H. Peter Anvin - All Rights Reserved
+#   Copyright 2003-2007 H. Peter Anvin - All Rights Reserved
 #
 #   Permission is hereby granted, free of charge, to any person
 #   obtaining a copy of this software and associated documentation
@@ -27,7 +27,9 @@
 
 # COM32 start up code - must be linked first in the binary
 
-
+/* Number of arguments in our version of the entry structure */
+#define COM32_ARGS 6
+	
 		.section ".init","ax"
 		.globl _start
 		.type _start, @function
@@ -49,7 +51,7 @@ _start:
 		# Copy COM32 invocation parameters
 		leal 4(%esp),%esi		# Argument list
 		movl $__com32,%edi
-		movl $5,%ecx
+		movl $COM32_ARGS,%ecx
 		movl %esp,-4(%edi)		# Save the initial stack ptr
 		cmpl (%esi),%ecx
 		jbe 1f
@@ -87,4 +89,4 @@ _start:
 		.globl __entry_esp
 __entry_esp:	.space 4
 		.globl __com32
-__com32:	.space 4*6
+__com32:	.space 4*(COM32_ARGS+1)
diff --git a/comboot.doc b/comboot.doc
index 3c806c3b..2939f9b7 100644
--- a/comboot.doc
+++ b/comboot.doc
@@ -85,6 +85,7 @@ The following arguments are passed to the program on the stack:
  [ESP+16] dword Pointer to low memory bounce buffer
  [ESP+20] dword Size of low memory bounce buffer
  [ESP+24] dword Pointer to FAR call helper function (new in 2.05)
+ [ESP+28] dword Pointer to CDECL helper function (new in 3.xx)
 
 This corresponds to the following C prototype, available in the file
 com32/include/com32.h:
@@ -95,7 +96,9 @@ int _start(unsigned int __nargs,
 	   void (*__intcall)(uint8_t, com32sys_t *, com32sys_t *),
 	   void *__bounce_ptr,
 	   unsigned int __bounce_len,
-	   void (*__farcall)(uint32_t, uint16_t, com32sys_t *, com32sys_t *));
+	   void (*__farcall)(uint32_t, com32sys_t *, com32sys_t *),
+	   int (*__cfarcall)(uint32_t, void *, size_t)
+	   );
 
 The intcall helper function can be used to issue BIOS or SYSLINUX API
 calls, and takes the interrupt number as first argument.  The second
@@ -138,6 +141,10 @@ The farcall helper function behaves similarly, but takes as its first
 argument the CS:IP (in the form (CS << 16) + IP) of procedure to be
 invoked via a FAR CALL.
 
+The cfarcall helper function takes (CS << 16)+IP, a pointer to a stack
+frame, a size of that stack frame, and returns the return value of EAX
+(which may need to be appropriate truncated by the user.)
+
 
 	++++ SYSLINUX API CALLS +++