core: add a direct 32-bit API

Add a direct 32-bit API to some functions; initially read file only.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 32 insertions, 13 deletions

diff --git a/doc/comboot.txt b/doc/comboot.txt
index 6d026aab..79506887 100644
--- a/doc/comboot.txt
+++ b/doc/comboot.txt
@@ -90,19 +90,22 @@ The following arguments are passed to the program on the stack:
  [ESP+24] dword Pointer to FAR call helper function (new in 2.05)
  [ESP+28] dword Pointer to CDECL helper function (new in 3.54)
  [ESP+32] dword Amount of memory controlled by the Syslinux core (new in 3.74)
-
-This corresponds to the following C prototype, available in the file
-com32/include/com32.h:
-
-/* The standard prototype for _start() */
-int _start(unsigned int __nargs,
-	   char *__cmdline,
-	   void (*__intcall)(uint8_t, com32sys_t *, com32sys_t *),
-	   void *__bounce_ptr,
-	   unsigned int __bounce_len,
-	   void (*__farcall)(uint32_t, com32sys_t *, com32sys_t *),
-	   int (*__cfarcall)(uint32_t, void *, size_t)
-	   );
+ [ESP+36] dword	Pointer to protected-mode functions (new in 4.00)
+
+The libcom32 startup code loads this into a structure named __com32,
+defined in <com32.h>:
+
+extern struct com32_sys_args {
+    uint32_t cs_sysargs;
+    char *cs_cmdline;
+    void __cdecl(*cs_intcall)(uint8_t, const com32sys_t *, com32sys_t *);
+    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);
+    uint32_t cs_memsize;
+    struct com32_pmapi *cs_pm;
+} __com32;
 
 The intcall helper function can be used to issue BIOS or Syslinux API
 calls, and takes the interrupt number as first argument.  The second
@@ -149,6 +152,12 @@ 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.)
 
+Starting in version 4.00, some of these API calls are available as
+protected-mode function calls, using the regparm(3) calling convention
+(the first three argumetns in EAX, EDX, ECX; the rest on the stack.)
+Those functions are defined in struct com32_pmapi, defined in
+<syslinux/pmapi.h>.
+
 
 	++++ SYSLINUX API CALLS +++
 
@@ -342,6 +351,16 @@ AX=0007h [2.08] Read file
 	WARNING: Calling this function with an invalid file handle
 	will probably crash the system.
 
+	32-BIT VERSION:
+
+	size_t cs_pm->read_file(uint16_t *handle, void *buf, size_t blocks)
+
+	handle	- file handle (input and output, set to zero on end of file)
+	buf	- buffer to write to
+	blocks	- number of blocks to read
+
+	Returns number of bytes read, or 0 on failure.
+
 
 AX=0008h [2.08] Close file