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Rearrange stack space to reduce memory footprint.

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The BSP only needs extra stack space during program initialisation. The APs
aren't running at that point, so by positioning the BSP stack above the AP
stacks, it can extend down into the AP stack space without causing any
problems.
This commit is contained in:
Martin Whitaker 2022-01-09 21:21:29 +00:00
parent a454174f3f
commit 0aa1b1fa97
3 changed files with 24 additions and 19 deletions
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11
boot/boot.h
View File

@ -5,15 +5,20 @@
* Definitions used in the boot code. Also defines exported symbols needed
* in the main code.
*
* Copyright (C) 2020 Martin Whitaker.
* Copyright (C) 2020-2022 Martin Whitaker.
*/
#define MAX_APS 64 /* Maximum number of active APs. This
only affects memory footprint, so
can be increased if needed */
#define BSP_STACK_SIZE 4096 /* Stack size for the BSP */
#define AP_STACK_SIZE 2048 /* Stack size for each AP */
// NOTE: Before the APs are started, the BSP stack can extend downwards into
// the area reserved for the AP stacks. So the stack size given here just
// needs to be enough for running the main application once initialisation
// is complete. The pmem initialisation needs ~12KB of stack, so make sure
// the total stack size is at least that.
#define PCPU_STACK_SIZE 2048 /* Stack size for each CPU core */
#define LOW_LOAD_ADDR 0x00010000 /* The low load address for the main program */
#define HIGH_LOAD_ADDR 0x00100000 /* The high load address for the main program */

16
boot/startup32.S
View File

@ -6,7 +6,7 @@
// It supports the 32-bit Linux boot protocol and EFI boot for the first
// boot of the BSP.
//
// Copyright (C) 2020 Martin Whitaker.
// Copyright (C) 2020-2022 Martin Whitaker.
//
// Derived from memtest86+ head.S:
//
@ -91,10 +91,10 @@ startup:
# Pick the correct stack.
call smp_my_pcpu_num
movl $AP_STACK_SIZE, %edx
movl $PCPU_STACK_SIZE, %edx
mul %edx
leal bsp_stack_top@GOTOFF(%ebx), %esp
addl %eax, %esp
subl %eax, %esp
# Initialise the GDT descriptor.
@ -557,14 +557,14 @@ first_boot:
.bss
.align 16
bsp_stack_base:
. = . + BSP_STACK_SIZE
bsp_stack_top:
ap_stacks_base:
. = . + (AP_STACK_SIZE * MAX_APS)
. = . + (PCPU_STACK_SIZE * MAX_APS)
ap_stacks_top:
bsp_stack_base:
. = . + PCPU_STACK_SIZE
bsp_stack_top:
startup_stack_base:
. = . + 64
startup_stack_top:

16
boot/startup64.S
View File

@ -6,7 +6,7 @@
// It supports both the 32-bit and 64-bit Linux boot protocols and EFI boot
// for the first boot of the BSP.
//
// Copyright (C) 2020 Martin Whitaker.
// Copyright (C) 2020-2022 Martin Whitaker.
//
// Derived from memtest86+ head.S:
//
@ -151,10 +151,10 @@ startup:
xorq %rax, %rax
call smp_my_pcpu_num
movl $AP_STACK_SIZE, %edx
movl $PCPU_STACK_SIZE, %edx
mul %edx
leaq bsp_stack_top(%rip), %rsp
addq %rax, %rsp
subq %rax, %rsp
# Initialise the pml4 and pdp tables.
@ -602,14 +602,14 @@ first_boot:
.bss
.align 16
bsp_stack_base:
. = . + BSP_STACK_SIZE
bsp_stack_top:
ap_stacks_base:
. = . + (AP_STACK_SIZE * MAX_APS)
. = . + (PCPU_STACK_SIZE * MAX_APS)
ap_stacks_top:
bsp_stack_base:
. = . + PCPU_STACK_SIZE
bsp_stack_top:
startup_stack_base:
. = . + 64
startup_stack_top: