--- /dev/null
+/*
+ * 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
Code Review / kvmfornfv.git / blobdiff