src/arch/i386/include/realmode.h

   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
  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
  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 */