• Home
  • Line#
  • Scopes#
  • Navigate#
  • Raw
  • Download
1 #ifndef REALMODE_H
2 #define REALMODE_H
3 
4 #include <stdint.h>
5 #include <registers.h>
6 #include <gpxe/uaccess.h>
7 
8 /*
9  * Data structures and type definitions
10  *
11  */
12 
13 FILE_LICENCE ( GPL2_OR_LATER );
14 
15 /*
16  * Declaration of variables in .data16
17  *
18  * To place a variable in the .data16 segment, declare it using the
19  * pattern:
20  *
21  *   int __data16 ( foo );
22  *   #define foo __use_data16 ( foo );
23  *
24  *   extern uint32_t __data16 ( bar );
25  *   #define bar __use_data16 ( bar );
26  *
27  *   static long __data16 ( baz ) = 0xff000000UL;
28  *   #define baz __use_data16 ( baz );
29  *
30  * i.e. take a normal declaration, add __data16() around the variable
31  * name, and add a line saying "#define <name> __use_data16 ( <name> )
32  *
33  * You can then access them just like any other variable, for example
34  *
35  *   int x = foo + bar;
36  *
37  * This magic is achieved at a cost of only around 7 extra bytes per
38  * group of accesses to .data16 variables.  When using KEEP_IT_REAL,
39  * there is no extra cost.
40  *
41  * You should place variables in .data16 when they need to be accessed
42  * by real-mode code.  Real-mode assembly (e.g. as created by
43  * REAL_CODE()) can access these variables via the usual data segment.
44  * You can therefore write something like
45  *
46  *   static uint16_t __data16 ( foo );
47  *   #define foo __use_data16 ( foo )
48  *
49  *   int bar ( void ) {
50  *     __asm__ __volatile__ ( REAL_CODE ( "int $0xff\n\t"
51  *                                        "movw %ax, foo" )
52  *                            : : );
53  *     return foo;
54  *   }
55  *
56  * Variables may also be placed in .text16 using __text16 and
57  * __use_text16.  Some variables (e.g. chained interrupt vectors) fit
58  * most naturally in .text16; most should be in .data16.
59  *
60  * If you have only a pointer to a magic symbol within .data16 or
61  * .text16, rather than the symbol itself, you can attempt to extract
62  * the underlying symbol name using __from_data16() or
63  * __from_text16().  This is not for the faint-hearted; check the
64  * assembler output to make sure that it's doing the right thing.
65  */
66 
67 /**
68  * Copy data to base memory
69  *
70  * @v dest_seg		Destination segment
71  * @v dest_off		Destination offset
72  * @v src		Source
73  * @v len		Length
74  */
75 static inline __always_inline void
copy_to_real(unsigned int dest_seg,unsigned int dest_off,void * src,size_t n)76 copy_to_real ( unsigned int dest_seg, unsigned int dest_off,
77 	       void *src, size_t n ) {
78 	copy_to_user ( real_to_user ( dest_seg, dest_off ), 0, src, n );
79 }
80 
81 /**
82  * Copy data to base memory
83  *
84  * @v dest		Destination
85  * @v src_seg		Source segment
86  * @v src_off		Source offset
87  * @v len		Length
88  */
89 static inline __always_inline void
copy_from_real(void * dest,unsigned int src_seg,unsigned int src_off,size_t n)90 copy_from_real ( void *dest, unsigned int src_seg,
91 		 unsigned int src_off, size_t n ) {
92 	copy_from_user ( dest, real_to_user ( src_seg, src_off ), 0, n );
93 }
94 
95 /**
96  * Write a single variable to base memory
97  *
98  * @v var		Variable to write
99  * @v dest_seg		Destination segment
100  * @v dest_off		Destination offset
101  */
102 #define put_real( var, dest_seg, dest_off ) \
103 	copy_to_real ( (dest_seg), (dest_off), &(var), sizeof (var) )
104 
105 /**
106  * Read a single variable from base memory
107  *
108  * @v var		Variable to read
109  * @v src_seg		Source segment
110  * @v src_off		Source offset
111  */
112 #define get_real( var, src_seg, src_off ) \
113 	copy_from_real ( &(var), (src_seg), (src_off), sizeof (var) )
114 
115 /*
116  * REAL_CODE ( asm_code_str )
117  *
118  * This can be used in inline assembly to create a fragment of code
119  * that will execute in real mode.  For example: to write a character
120  * to the BIOS console using INT 10, you would do something like:
121  *
122  *     __asm__ __volatile__ ( REAL_CODE ( "int $0x16" )
123  *			      : "=a" ( character ) : "a" ( 0x0000 ) );
124  *
125  */
126 
127 #endif /* REALMODE_H */
128