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syscall: do not use cr2 as a scratch register

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Matheus
2026-04-02 01:45:17 -03:00
parent e443319433
commit 5b164793cf
2 changed files with 5 additions and 7 deletions
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kernel-src/arch/x86-64/syscall.asm
+3 -7
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@@ -225,10 +225,7 @@ global arch_syscall_entry
; rax has return value ; rax has return value
arch_syscall_entry: arch_syscall_entry:
swapgs swapgs
; saving the syscall number on cr2 is cursed but we need this extra register mov [gs:40], rax ; save syscall number
; and taking a page fault here would result in a triple fault anyways
; because it's still using the user stack
mov cr2, rax
; rax can be used just fine now ; rax can be used just fine now
mov rax, [gs:0] ; thread pointer mov rax, [gs:0] ; thread pointer
mov rax, [rax] ; kernel stack top mov rax, [rax] ; kernel stack top
@@ -237,7 +234,7 @@ arch_syscall_entry:
; push context ; push context
push qword 0x1b ; user SS push qword 0x1b ; user SS
push qword rax ; user RSP push qword rax ; user RSP
mov rax, cr2 ; restore syscall number mov rax, [gs:40] ; restore syscall number
push r11 ; rflags is stored in r11 push r11 ; rflags is stored in r11
push qword 0x23 ; user CS push qword 0x23 ; user CS
push qword rcx ; save return RIP push qword rcx ; save return RIP
@@ -266,8 +263,7 @@ arch_syscall_entry:
push rbx push rbx
mov rbx, gs mov rbx, gs
push rbx push rbx
mov rbx, cr2 sub rsp, 8 ; cr2
push rbx
mov rbx, 0x10 mov rbx, 0x10
mov es, rbx mov es, rbx
kernel-src/include/x86-64/arch/cpu.h
+2
View File
@@ -28,6 +28,8 @@ typedef struct cpu_t {
long hardware_id; // expected to be here by other code long hardware_id; // expected to be here by other code
long internal_id; // expected to be here by other code long internal_id; // expected to be here by other code
uint64_t scratch; // expected to be here by other code
timekeeper_source_t *timekeeper_source; timekeeper_source_t *timekeeper_source;
timekeeper_source_info_t *timekeeper_source_info; timekeeper_source_info_t *timekeeper_source_info;
time_t timekeeper_source_base_ticks; time_t timekeeper_source_base_ticks;