diff options
Diffstat (limited to 'contrib/syslinux-4.02/gpxe/src/arch/i386/transitions/libkir.S')
| -rw-r--r-- | contrib/syslinux-4.02/gpxe/src/arch/i386/transitions/libkir.S | 256 |
1 files changed, 256 insertions, 0 deletions
diff --git a/contrib/syslinux-4.02/gpxe/src/arch/i386/transitions/libkir.S b/contrib/syslinux-4.02/gpxe/src/arch/i386/transitions/libkir.S new file mode 100644 index 0000000..1176fcc --- /dev/null +++ b/contrib/syslinux-4.02/gpxe/src/arch/i386/transitions/libkir.S @@ -0,0 +1,256 @@ +/* + * libkir: a transition library for -DKEEP_IT_REAL + * + * Michael Brown <mbrown@fensystems.co.uk> + * + */ + +FILE_LICENCE ( GPL2_OR_LATER ) + +/**************************************************************************** + * This file defines libkir: an interface between external and + * internal environments when -DKEEP_IT_REAL is used, so that both + * internal and external environments are in real mode. It deals with + * switching data segments and the stack. It provides the following + * functions: + * + * ext_to_kir & switch between external and internal (kir) + * kir_to_ext environments, preserving all non-segment + * registers + * + * kir_call issue a call to an internal routine from external + * code + * + * libkir is written to avoid assuming that segments are anything + * other than opaque data types, and also avoids assuming that the + * stack pointer is 16-bit. This should enable it to run just as well + * in 16:16 or 16:32 protected mode as in real mode. + **************************************************************************** + */ + +/* Breakpoint for when debugging under bochs */ +#define BOCHSBP xchgw %bx, %bx + + .text + .arch i386 + .section ".text16", "awx", @progbits + .code16 + +/**************************************************************************** + * init_libkir (real-mode or 16:xx protected-mode far call) + * + * Initialise libkir ready for transitions to the kir environment + * + * Parameters: + * %cs : .text16 segment + * %ds : .data16 segment + **************************************************************************** + */ + .globl init_libkir +init_libkir: + /* Record segment registers */ + pushw %ds + popw %cs:kir_ds + lret + +/**************************************************************************** + * ext_to_kir (real-mode or 16:xx protected-mode near call) + * + * Switch from external stack and segment registers to internal stack + * and segment registers. %ss:sp is restored from the saved kir_ds + * and kir_sp. %ds, %es, %fs and %gs are all restored from the saved + * kir_ds. All other registers are preserved. + * + * %cs:0000 must point to the start of the runtime image code segment + * on entry. + * + * Parameters: none + **************************************************************************** + */ + + .globl ext_to_kir +ext_to_kir: + /* Record external segment registers */ + movw %ds, %cs:ext_ds + pushw %cs + popw %ds /* Set %ds = %cs for easier access to variables */ + movw %es, %ds:ext_es + movw %fs, %ds:ext_fs + movw %gs, %ds:ext_fs + + /* Preserve registers */ + movw %ax, %ds:save_ax + + /* Extract near return address from stack */ + popw %ds:save_retaddr + + /* Record external %ss:esp */ + movw %ss, %ds:ext_ss + movl %esp, %ds:ext_esp + + /* Load internal segment registers and stack pointer */ + movw %ds:kir_ds, %ax + movw %ax, %ss + movzwl %ds:kir_sp, %esp + movw %ax, %ds + movw %ax, %es + movw %ax, %fs + movw %ax, %gs +1: + + /* Place return address on new stack */ + pushw %cs:save_retaddr + + /* Restore registers and return */ + movw %cs:save_ax, %ax + ret + +/**************************************************************************** + * kir_to_ext (real-mode or 16:xx protected-mode near call) + * + * Switch from internal stack and segment registers to external stack + * and segment registers. %ss:%esp is restored from the saved ext_ss + * and ext_esp. Other segment registers are restored from the + * corresponding locations. All other registers are preserved. + * + * Note that it is actually %ss that is recorded as kir_ds, on the + * assumption that %ss == %ds when kir_to_ext is called. + * + * Parameters: none + **************************************************************************** + */ + + .globl kir_to_ext +kir_to_ext: + /* Record near return address */ + pushw %cs + popw %ds /* Set %ds = %cs for easier access to variables */ + popw %ds:save_retaddr + + /* Record internal segment registers and %sp */ + movw %ss, %ds:kir_ds + movw %sp, %ds:kir_sp + + /* Load external segment registers and stack pointer */ + movw %ds:ext_ss, %ss + movl %ds:ext_esp, %esp + movw %ds:ext_gs, %gs + movw %ds:ext_fs, %fs + movw %ds:ext_es, %es + movw %ds:ext_ds, %ds + + /* Return */ + pushw %cs:save_retaddr + ret + +/**************************************************************************** + * kir_call (real-mode or 16:xx protected-mode far call) + * + * Call a specific C function in the internal code. The prototype of + * the C function must be + * void function ( struct i386_all_resg *ix86 ); + * ix86 will point to a struct containing the real-mode registers + * at entry to kir_call. + * + * All registers will be preserved across kir_call(), unless the C + * function explicitly overwrites values in ix86. Interrupt status + * will also be preserved. + * + * Parameters: + * function : (32-bit) virtual address of C function to call + * + * Example usage: + * pushl $pxe_api_call + * lcall $UNDI_CS, $kir_call + * addw $4, %sp + * to call in to the C function + * void pxe_api_call ( struct i386_all_regs *ix86 ); + **************************************************************************** + */ + + .globl kir_call +kir_call: + /* Preserve flags. Must do this before any operation that may + * affect flags. + */ + pushfl + popl %cs:save_flags + + /* Disable interrupts. We do funny things with the stack, and + * we're not re-entrant. + */ + cli + + /* Extract address of internal routine from stack. We must do + * this without using (%bp), because we may be called with + * either a 16-bit or a 32-bit stack segment. + */ + popl %cs:save_retaddr /* Scratch location */ + popl %cs:save_function + subl $8, %esp /* Restore %esp */ + + /* Switch to internal stack. Note that the external stack is + * inaccessible once we're running internally (since we have + * no concept of 48-bit far pointers) + */ + call ext_to_kir + + /* Store external registers on internal stack */ + pushl %cs:save_flags + pushal + pushl %cs:ext_fs_and_gs + pushl %cs:ext_ds_and_es + pushl %cs:ext_cs_and_ss + + /* Push &ix86 on stack and call function */ + sti + pushl %esp + data32 call *%cs:save_function + popl %eax /* discard */ + + /* Restore external registers from internal stack */ + popl %cs:ext_cs_and_ss + popl %cs:ext_ds_and_es + popl %cs:ext_fs_and_gs + popal + popl %cs:save_flags + + /* Switch to external stack */ + call kir_to_ext + + /* Restore flags */ + pushl %cs:save_flags + popfl + + /* Return */ + lret + +/**************************************************************************** + * Stored internal and external stack and segment registers + **************************************************************************** + */ + +ext_cs_and_ss: +ext_cs: .word 0 +ext_ss: .word 0 +ext_ds_and_es: +ext_ds: .word 0 +ext_es: .word 0 +ext_fs_and_gs: +ext_fs: .word 0 +ext_gs: .word 0 +ext_esp: .long 0 + + .globl kir_ds +kir_ds: .word 0 + .globl kir_sp +kir_sp: .word _estack + +/**************************************************************************** + * Temporary variables + **************************************************************************** + */ +save_ax: .word 0 +save_retaddr: .long 0 +save_flags: .long 0 +save_function: .long 0 |