iPXE
Functions
bootsector.h File Reference

x86 bootsector image format More...

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Functions

 FILE_LICENCE (GPL2_OR_LATER_OR_UBDL)
 
int call_bootsector (unsigned int segment, unsigned int offset, unsigned int drive)
 Jump to preloaded bootsector. More...
 

Detailed Description

x86 bootsector image format

Definition in file bootsector.h.

Function Documentation

◆ FILE_LICENCE()

FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL  )

◆ call_bootsector()

int call_bootsector ( unsigned int  segment,
unsigned int  offset,
unsigned int  drive 
)

Jump to preloaded bootsector.

Parameters
segmentReal-mode segment
offsetReal-mode offset
driveDrive number to pass to boot sector
Return values
rcReturn status code

Definition at line 64 of file bootsector.c.

65  {
66  int discard_b, discard_D, discard_d;
67 
68  /* Reset console, since boot sector will probably use it */
69  console_reset();
70 
71  DBG ( "Booting from boot sector at %04x:%04x\n", segment, offset );
72 
73  /* Hook INTs 18 and 19 to capture failure paths */
74  hook_bios_interrupt ( 0x18, ( intptr_t ) bootsector_exec_fail,
75  &int18_vector );
76  hook_bios_interrupt ( 0x19, ( intptr_t ) bootsector_exec_fail,
77  &int19_vector );
78 
79  /* Boot the loaded sector
80  *
81  * We assume that the boot sector may completely destroy our
82  * real-mode stack, so we preserve everything we need in
83  * static storage.
84  */
85  __asm__ __volatile__ ( REAL_CODE ( /* Save return address off-stack */
86  "popw %%cs:saved_retaddr\n\t"
87  /* Save stack pointer */
88  "movw %%ss, %%ax\n\t"
89  "movw %%ax, %%cs:saved_ss\n\t"
90  "movw %%sp, %%cs:saved_sp\n\t"
91  /* Save frame pointer (gcc bug) */
92  "movl %%ebp, %%cs:saved_ebp\n\t"
93  /* Prepare jump to boot sector */
94  "pushw %%bx\n\t"
95  "pushw %%di\n\t"
96  /* Clear all registers */
97  "xorl %%eax, %%eax\n\t"
98  "xorl %%ebx, %%ebx\n\t"
99  "xorl %%ecx, %%ecx\n\t"
100  /* %edx contains drive number */
101  "xorl %%esi, %%esi\n\t"
102  "xorl %%edi, %%edi\n\t"
103  "xorl %%ebp, %%ebp\n\t"
104  "movw %%ax, %%ds\n\t"
105  "movw %%ax, %%es\n\t"
106  "movw %%ax, %%fs\n\t"
107  "movw %%ax, %%gs\n\t"
108  /* Jump to boot sector */
109  "sti\n\t"
110  "lret\n\t"
111  /* Preserved variables */
112  "\nsaved_ebp: .long 0\n\t"
113  "\nsaved_ss: .word 0\n\t"
114  "\nsaved_sp: .word 0\n\t"
115  "\nsaved_retaddr: .word 0\n\t"
116  /* Boot failure return point */
117  "\nbootsector_exec_fail:\n\t"
118  /* Restore frame pointer (gcc bug) */
119  "movl %%cs:saved_ebp, %%ebp\n\t"
120  /* Restore stack pointer */
121  "movw %%cs:saved_ss, %%ax\n\t"
122  "movw %%ax, %%ss\n\t"
123  "movw %%cs:saved_sp, %%sp\n\t"
124  /* Return via saved address */
125  "jmp *%%cs:saved_retaddr\n\t" )
126  : "=b" ( discard_b ), "=D" ( discard_D ),
127  "=d" ( discard_d )
128  : "b" ( segment ), "D" ( offset ),
129  "d" ( drive )
130  : "eax", "ecx", "esi" );
131 
132  DBG ( "Booted disk returned via INT 18 or 19\n" );
133 
134  /* Unhook INTs 18 and 19 */
135  unhook_bios_interrupt ( 0x18, ( intptr_t ) bootsector_exec_fail,
136  &int18_vector );
137  unhook_bios_interrupt ( 0x19, ( intptr_t ) bootsector_exec_fail,
138  &int19_vector );
139 
140  return -ECANCELED;
141 }
segment
uint16_t segment
Code segment.
Definition: librm.h:252
bootsector_exec_fail
void bootsector_exec_fail(void)
Restart point for INT 18 or 19.
drive
uint8_t drive
Drive number.
Definition: int13.h:16
intptr_t
unsigned long intptr_t
Definition: stdint.h:21
ECANCELED
#define ECANCELED
Operation canceled.
Definition: errno.h:343
hook_bios_interrupt
void hook_bios_interrupt(unsigned int interrupt, unsigned int handler, struct segoff *chain_vector)
Hook INT vector.
Definition: biosint.c:24
unhook_bios_interrupt
int unhook_bios_interrupt(unsigned int interrupt, unsigned int handler, struct segoff *chain_vector)
Unhook INT vector.
Definition: biosint.c:69
offset
static userptr_t size_t offset
Offset of the first segment within the content.
Definition: deflate.h:259
int18_vector
static struct segoff int18_vector
Vector for storing original INT 18 handler.
Definition: bootsector.c:44
console_reset
static void console_reset(void)
Reset console.
Definition: console.h:214
__volatile__
__asm__ __volatile__("\n1:\n\t" "movb -1(%3,%1), %%al\n\t" "stosb\n\t" "loop 1b\n\t" "xorl %%eax, %%eax\n\t" "mov %4, %1\n\t" "rep stosb\n\t" :"=&D"(discard_D), "=&c"(discard_c), "+m"(*value) :"r"(data), "g"(pad_len), "0"(value0), "1"(len) :"eax")
discard_D
void * discard_D
Definition: bigint.h:31
int19_vector
static struct segoff int19_vector
Vector for storing original INT 19 handler.
Definition: bootsector.c:51
__asm__
__asm__(".section \".rodata\", \"a\", " PROGBITS "\n\t" "\nprivate_key_data:\n\t" ".size private_key_data, ( . - private_key_data )\n\t" ".equ private_key_len, ( . - private_key_data )\n\t" ".previous\n\t")
DBG
#define DBG(...)
Print a debugging message.
Definition: compiler.h:498
REAL_CODE
#define REAL_CODE(asm_code_str)
Definition: libkir.h:226

References __asm__(), __volatile__(), bootsector_exec_fail(), console_reset(), DBG, discard_D, drive, ECANCELED, hook_bios_interrupt(), int18_vector, int19_vector, offset, REAL_CODE, segment, and unhook_bios_interrupt().

Referenced by int13_boot().

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