source: bootcd/isolinux/syslinux-6.03/gpxe/src/arch/i386/include/libkir.h

#ifndef LIBKIR_H
#define LIBKIR_H

#include "realmode.h"

#ifndef ASSEMBLY

/*
 * Full API documentation for these functions is in realmode.h.
 *
 */

/* Access to variables in .data16 and .text16 in a way compatible with librm */
#define __data16( variable ) variable
#define __data16_array( variable, array ) variable array
#define __bss16( variable ) variable
#define __bss16_array( variable, array ) variable array
#define __text16( variable ) variable
#define __text16_array( variable,array ) variable array
#define __use_data16( variable ) variable
#define __use_text16( variable ) variable
#define __from_data16( pointer ) pointer
#define __from_text16( pointer ) pointer

/* Real-mode data and code segments */
static inline __attribute__ (( always_inline )) unsigned int _rm_cs ( void ) {
        uint16_t cs;
        __asm__ __volatile__ ( "movw %%cs, %w0" : "=r" ( cs ) );
        return cs;
}

static inline __attribute__ (( always_inline )) unsigned int _rm_ds ( void ) {
        uint16_t ds;
        __asm__ __volatile__ ( "movw %%ds, %w0" : "=r" ( ds ) );
        return ds;
}

#define rm_cs ( _rm_cs() )
#define rm_ds ( _rm_ds() )

/* Copy to/from base memory */

static inline void copy_to_real_libkir ( unsigned int dest_seg,
                                         unsigned int dest_off,
                                         const void *src, size_t n ) {
        unsigned int discard_D, discard_S, discard_c;

        __asm__ __volatile__ ( "pushw %%es\n\t"
                               "movw %3, %%es\n\t"
                               "rep movsb\n\t"
                               "popw %%es\n\t"
                               : "=D" ( discard_D ), "=S" ( discard_S ),
                                 "=c" ( discard_c )
                               : "r" ( dest_seg ), "D" ( dest_off ),
                                 "S" ( src ),
                                 "c" ( n )
                               : "memory" );
}

static inline void copy_from_real_libkir ( void *dest,
                                           unsigned int src_seg,
                                           unsigned int src_off,
                                           size_t n ) {
        unsigned int discard_D, discard_S, discard_c;

        __asm__ __volatile__ ( "pushw %%ds\n\t"
                               "movw %4, %%ds\n\t"
                               "rep movsb\n\t"
                               "popw %%ds\n\t"
                               : "=D" ( discard_D ), "=S" ( discard_S ),
                                 "=c" ( discard_c )
                               : "D" ( dest ),
                                 "r" ( src_seg ), "S" ( src_off ),
                                 "c" ( n )
                               : "memory" );
}

#define copy_to_real copy_to_real_libkir
#define copy_from_real copy_from_real_libkir

/*
 * Transfer individual values to/from base memory.  There may well be
 * a neater way to do this.  We have two versions: one for constant
 * offsets (where the mov instruction must be of the form "mov
 * %es:123, %xx") and one for non-constant offsets (where the mov
 * instruction must be of the form "mov %es:(%xx), %yx".  If it's
 * possible to incorporate both forms into one __asm__ instruction, I
 * don't know how to do it.
 *
 * Ideally, the mov instruction should be "mov%z0"; the "%z0" is meant
 * to expand to either "b", "w" or "l" depending on the size of
 * operand 0.  This would remove the (minor) ambiguity in the mov
 * instruction.  However, gcc on at least my system barfs with an
 * "internal compiler error" when confronted with %z0.
 *
 */

#define put_real_kir_const_off( var, seg, off )                              \
        __asm__ ( "movw %w1, %%es\n\t"                                       \
                  "mov %0, %%es:%c2\n\t"                                     \
                  "pushw %%ds\n\t" /* restore %es */                         \
                  "popw %%es\n\t"                                            \
                  :                                                          \
                  : "r,r" ( var ), "rm,rm" ( seg ), "i,!r" ( off )           \
                  )

#define put_real_kir_nonconst_off( var, seg, off )                           \
        __asm__ ( "movw %w1, %%es\n\t"                                       \
                  "mov %0, %%es:(%2)\n\t"                                    \
                  "pushw %%ds\n\t" /* restore %es */                         \
                  "popw %%es\n\t"                                            \
                  :                                                          \
                  : "r" ( var ), "rm" ( seg ), "r" ( off )                   \
                  )

#define put_real_kir( var, seg, off )                                        \
        do {                                                                 \
          if ( __builtin_constant_p ( off ) )                                \
                  put_real_kir_const_off ( var, seg, off );                  \
          else                                                               \
                  put_real_kir_nonconst_off ( var, seg, off );               \
        } while ( 0 )

#define get_real_kir_const_off( var, seg, off )                              \
        __asm__ ( "movw %w1, %%es\n\t"                                       \
                  "mov %%es:%c2, %0\n\t"                                     \
                  "pushw %%ds\n\t" /* restore %es */                         \
                  "popw %%es\n\t"                                            \
                  : "=r,r" ( var )                                           \
                  : "rm,rm" ( seg ), "i,!r" ( off )                          \
                  )

#define get_real_kir_nonconst_off( var, seg, off )                           \
        __asm__ ( "movw %w1, %%es\n\t"                                       \
                  "mov %%es:(%2), %0\n\t"                                    \
                  "pushw %%ds\n\t" /* restore %es */                         \
                  "popw %%es\n\t"                                            \
                  : "=r" ( var )                                             \
                  : "rm" ( seg ), "r" ( off )                                \
                  )

#define get_real_kir( var, seg, off )                                        \
        do {                                                                 \
          if ( __builtin_constant_p ( off ) )                                \
                  get_real_kir_const_off ( var, seg, off );                  \
          else                                                               \
                  get_real_kir_nonconst_off ( var, seg, off );               \
        } while ( 0 )

#define put_real put_real_kir
#define get_real get_real_kir

/**
 * A pointer to a user buffer
 *
 * This is actually a struct segoff, but encoded as a uint32_t to
 * ensure that gcc passes it around efficiently.
 */
typedef uint32_t userptr_t;

/**
 * Copy data to user buffer
 *
 * @v buffer    User buffer
 * @v offset    Offset within user buffer
 * @v src       Source
 * @v len       Length
 */
static inline __attribute__ (( always_inline )) void
copy_to_user ( userptr_t buffer, off_t offset, const void *src, size_t len ) {
        copy_to_real ( ( buffer >> 16 ), ( ( buffer & 0xffff ) + offset ),
                       src, len );
}

/**
 * Copy data from user buffer
 *
 * @v dest      Destination
 * @v buffer    User buffer
 * @v offset    Offset within user buffer
 * @v len       Length
 */
static inline __attribute__ (( always_inline )) void
copy_from_user ( void *dest, userptr_t buffer, off_t offset, size_t len ) {
        copy_from_real ( dest, ( buffer >> 16 ),
                         ( ( buffer & 0xffff ) + offset ), len );
}

/**
 * Convert segment:offset address to user buffer
 *
 * @v segment   Real-mode segment
 * @v offset    Real-mode offset
 * @ret buffer  User buffer
 */
static inline __attribute__ (( always_inline )) userptr_t
real_to_user ( unsigned int segment, unsigned int offset ) {
        return ( ( segment << 16 ) | offset );
}

/**
 * Convert virtual address to user buffer
 *
 * @v virtual   Virtual address
 * @ret buffer  User buffer
 *
 * This constructs a user buffer from an ordinary pointer.  Use it
 * when you need to pass a pointer to an internal buffer to a function
 * that expects a @c userptr_t.
 */
static inline __attribute__ (( always_inline )) userptr_t
virt_to_user ( void * virtual ) {
        return real_to_user ( rm_ds, ( intptr_t ) virtual );
}

/* TEXT16_CODE: declare a fragment of code that resides in .text16 */
#define TEXT16_CODE( asm_code_str )                     \
        ".section \".text16\", \"ax\", @progbits\n\t"   \
        ".code16\n\t"                                   \
        ".arch i386\n\t"                                \
        asm_code_str "\n\t"                             \
        ".code16gcc\n\t"                                \
        ".previous\n\t"

/* REAL_CODE: declare a fragment of code that executes in real mode */
#define REAL_CODE( asm_code_str )       \
        ".code16\n\t"                   \
        asm_code_str "\n\t"             \
        ".code16gcc\n\t"

#endif /* ASSEMBLY */

#endif /* LIBKIR_H */