From ae9c1d1b16061242068353ff9064c8c9ef63b577 Mon Sep 17 00:00:00 2001
From: dzwdz
Date: Sat, 24 Jul 2021 18:53:34 +0200
Subject: sysexit() now overrides all registers

when doing anything more complex than starting a new program, you pretty
much need to pass a full register dump. otherwise stuff will break
---
 src/kernel/arch/generic.h        |  2 +-
 src/kernel/arch/i386/registers.h |  6 ++++++
 src/kernel/arch/i386/sysenter.c  | 21 +++++++++++++++++++++
 src/kernel/arch/i386/sysenter.s  | 12 ++++++------
 4 files changed, 34 insertions(+), 7 deletions(-)

(limited to 'src/kernel/arch')

diff --git a/src/kernel/arch/generic.h b/src/kernel/arch/generic.h
index f208aa3..d5f8b3c 100644
--- a/src/kernel/arch/generic.h
+++ b/src/kernel/arch/generic.h
@@ -16,7 +16,7 @@ __attribute__((noreturn))
 void halt_cpu();
 
 // src/arch/i386/sysenter.s
-void sysexit(void (*fun)(), void *stack_top);
+void sysexit(struct registers);
 int syscall_handler(int, int, int, int);
 
 // all of those can allocate memory
diff --git a/src/kernel/arch/i386/registers.h b/src/kernel/arch/i386/registers.h
index feba157..1264139 100644
--- a/src/kernel/arch/i386/registers.h
+++ b/src/kernel/arch/i386/registers.h
@@ -1,11 +1,17 @@
 #pragma once
 #include <stdint.h>
 
+// TODO merge registers and registers_pushad
+
 struct registers {
 	uint32_t eax, ebx, ecx, edx, esi, edi;
 	void *ebp, *esp, *eip;
 };
 
+struct registers_pushad {
+	uint32_t edi, esi, ebp, esp, ebx, edx, ecx, eax;
+} __attribute__((__packed__));
+
 // saves a return value according to the SysV ABI
 inline void regs_savereturn(struct registers *regs, uint64_t value) {
 	regs->eax = value;
diff --git a/src/kernel/arch/i386/sysenter.c b/src/kernel/arch/i386/sysenter.c
index 91dac2e..f3f5987 100644
--- a/src/kernel/arch/i386/sysenter.c
+++ b/src/kernel/arch/i386/sysenter.c
@@ -1,6 +1,27 @@
 #include <kernel/arch/generic.h>
 #include <kernel/proc.h>
 
+struct registers_pushad _sysexit_regs; // a hack
+
+extern void _sysexit_real();
+
+void sysexit(struct registers regs) {
+	_sysexit_regs = (struct registers_pushad) {
+		.eax = regs.eax,
+		.ebx = regs.ebx,
+		.ebp = regs.ebp,
+		.esi = regs.esi,
+		.edi = regs.edi,
+
+		// sysexit args
+		.ecx = regs.esp,
+		.edx = regs.eip,
+
+		// ESP doesn't matter
+	};
+	_sysexit_real();
+}
+
 void sysenter_stage2(int edi, int esi, void *ebp, void *esp,
                      int ebx, int edx, int   ecx, int   eax)
 {
diff --git a/src/kernel/arch/i386/sysenter.s b/src/kernel/arch/i386/sysenter.s
index a982dd8..24cbc89 100644
--- a/src/kernel/arch/i386/sysenter.s
+++ b/src/kernel/arch/i386/sysenter.s
@@ -8,12 +8,9 @@
 .set IA32_SYSENTER_EIP, 0x176
 
 .section .text
-.global sysexit
-.type sysexit, @function
-sysexit:
-	mov 4(%esp), %edx
-	mov 8(%esp), %ecx
-
+.global _sysexit_real
+.type _sysexit_real, @function
+_sysexit_real:
 	mov $(SEG_r3data << 3 | 3), %ax
 	mov %ax, %ds
 	mov %ax, %es
@@ -25,6 +22,9 @@ sysexit:
 	or $0x80000000, %eax
 	mov %eax, %cr0
 
+	// restore the registers
+	mov $_sysexit_regs, %esp
+	popal // probably a bad idea
 	sysexit
 
 
-- 
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