This took some time to figure out.
Involves a hand-crafted 16 bit assembly instruction [1]
because it requires an immediate for the memory address
of far jump. This required self-modifying code
to inject the next instruction, therefore I added a near
jump to clear the instruction cache queue in case the pipeline
cached the unmodified jump location.
[1] Intel Architecture Software Developer's Manual,
Volume 2: Instruction Set Reference Manual
---
i386/i386/cpuboot.S | 36 +++++++++++++++++++++++++++++-------
i386/i386/mp_desc.c | 5 +++--
i386/i386/mp_desc.h | 7 +++++--
i386/i386at/model_dep.c | 18 ++++++++++++++++++
4 files changed, 55 insertions(+), 11 deletions(-)
diff --git a/i386/i386/cpuboot.S b/i386/i386/cpuboot.S
index 13d9160e..b2f9e520 100644
--- a/i386/i386/cpuboot.S
+++ b/i386/i386/cpuboot.S
@@ -23,15 +23,14 @@
#include <i386/seg.h>
#include <i386/gdt.h>
-#define AP_BOOT_ADDR 0x7000
-#define M(addr) (addr - apboot + AP_BOOT_ADDR)
+#define M(addr) (addr - apboot)
#define CR0_CLEAR_FLAGS_CACHE_ENABLE (CR0_CD | CR0_NW)
#define CR0_SET_FLAGS (CR0_CLEAR_FLAGS_CACHE_ENABLE | CR0_PE)
-#define CR0_CLEAR_FLAGS (CR0_PG | CR0_AM | CR0_WP | CR0_NE | CR0_TS | CR0_EM |
CR0_MP)
+#define CR0_CLEAR_FLAGS (CR0_PG | CR0_AM | CR0_WP | CR0_NE | CR0_TS |
CR0_EM | CR0_MP)
#define BOOT_CS 0x8
#define BOOT_DS 0x10
-.text
+.data
.align 16
apboot_idt_ptr:
@@ -101,16 +100,22 @@ apboot_percpu_med:
apboot_percpu_high:
.byte 0
-.globl apboot, apbootend
+.globl apboot, apbootend, gdt_descr_tmp
.align 16
.code16
apboot:
_apboot:
+ /* This is now address CS:0 in real mode */
+
+ /* Set data seg same as code seg */
+ mov %cs, %dx
+ mov %dx, %ds
+
cli
xorl %eax, %eax
movl %eax, %cr3
- mov %ax, %ds
+
mov %ax, %es
mov %ax, %fs
mov %ax, %gs
@@ -123,9 +128,26 @@ _apboot:
orl $CR0_SET_FLAGS, %eax
movl %eax, %cr0
- ljmp $BOOT_CS, $M(0f)
+ xorl %eax, %eax
+ mov %cs, %ax
+ shll $4, %eax
+ addl $M(0f), %eax
+ movl %eax, M(ljmp_offset32)
+
+ /* Flush cached instruction queue */
+ jmp 1f
+1:
+
+ /* ljmpl with relocation */
+ .byte 0x66
+ .byte 0xea
+ljmp_offset32:
+ .long 0xffffffff
+ .word BOOT_CS
+
0:
.code32
+ /* Protected mode! */
movw $BOOT_DS, %ax
movw %ax, %ds
movw %ax, %es
diff --git a/i386/i386/mp_desc.c b/i386/i386/mp_desc.c
index 860bbd9e..071aa292 100644
--- a/i386/i386/mp_desc.c
+++ b/i386/i386/mp_desc.c
@@ -99,6 +99,7 @@ interrupt_stack_alloc(void)
*/
int bspdone;
+phys_addr_t apboot_addr;
extern void *apboot, *apbootend;
extern volatile ApicLocalUnit* lapic;
@@ -297,7 +298,7 @@ cpu_start(int cpu)
printf("Trying to enable: %d\n", apic_id);
- smp_startup_cpu(apic_id, AP_BOOT_ADDR);
+ smp_startup_cpu(apic_id, apboot_addr);
printf("Started cpu %d (lapic id %04x)\n", cpu, apic_id);
@@ -310,7 +311,7 @@ start_other_cpus(void)
int ncpus = smp_get_numcpus();
//Copy cpu initialization assembly routine
- memcpy((void*)phystokv(AP_BOOT_ADDR), (void*) &apboot,
+ memcpy((void*) phystokv(apboot_addr), (void*) &apboot,
(uint32_t)&apbootend - (uint32_t)&apboot);
unsigned cpu;
diff --git a/i386/i386/mp_desc.h b/i386/i386/mp_desc.h
index fea42cd3..bcc68662 100644
--- a/i386/i386/mp_desc.h
+++ b/i386/i386/mp_desc.h
@@ -46,8 +46,6 @@
#include "gdt.h"
#include "ldt.h"
-#define AP_BOOT_ADDR 0x7000
-
/*
* The descriptor tables are together in a structure
* allocated one per processor (except for the boot processor).
@@ -78,6 +76,11 @@ extern uint8_t solid_intstack[];
extern int bspdone;
+/*
+ * Address to hold AP boot code, held in ASM
+ */
+extern phys_addr_t apboot_addr;
+
/*
* Each CPU calls this routine to set up its descriptor tables.
*/
diff --git a/i386/i386at/model_dep.c b/i386/i386at/model_dep.c
index 9dbe7e01..e0995c96 100644
--- a/i386/i386at/model_dep.c
+++ b/i386/i386at/model_dep.c
@@ -66,6 +66,7 @@
#include <i386/locore.h>
#include <i386/model_dep.h>
#include <i386/smp.h>
+#include <i386/seg.h>
#include <i386at/acpi_parse_apic.h>
#include <i386at/autoconf.h>
#include <i386at/biosmem.h>
@@ -125,6 +126,9 @@ char *kernel_cmdline = "";
extern char version[];
+/* Realmode temporary GDT */
+extern struct pseudo_descriptor gdt_descr_tmp;
+
/* If set, reboot the system on ctrl-alt-delete. */
boolean_t rebootflag = FALSE; /* exported to kdintr */
@@ -207,6 +211,20 @@ void machine_init(void)
*/
pmap_unmap_page_zero();
#endif
+
+#ifdef APIC
+ /*
+ * Grab an early page for AP boot code
+ */
+ /* FIXME: this may not allocate from below 1MB, if within first 16MB */
+ apboot_addr = vm_page_to_pa(vm_page_grab_contig(PAGE_SIZE,
VM_PAGE_SEL_DMA));
+ assert (apboot_addr < 0x100000);
+
+ /*
+ * Patch the realmode gdt with the correct offset
+ */
+ gdt_descr_tmp.linear_base += apboot_addr;
+#endif
}
/* Conserve power on processor CPU. */
--
2.43.0
