*: use a generic UserRegs type everywhere I'm storing registers

mostly inspired by Plan 9's Ureg, probably obvious from the name

4 files changed, 47 insertions, 10 deletions

diff --git a/src/kernel/arch/amd64/regs.c b/src/kernel/arch/amd64/regs.c
new file mode 100644
index 0000000..bb4e5aa
--- /dev/null
+++ b/src/kernel/arch/amd64/regs.c
@@ -0,0 +1,26 @@
+#include <kernel/arch/generic.h>
+#include <kernel/panic.h>
+
+void
+regs_safecopy(UserRegs *dst, const UserRegs *src)
+{
+	/* preserved flags: (see intel vol 1 3.4.3.)
+	 * 1<<0 = CF, carry flag
+	 * 1<<2 = PF, parity flag
+	 * 1<<4 = AC, auxilary carry
+	 * 1<<6 = ZF, zero flag
+	 * 1<<7 = SF, sign flag
+	 * 1<<11 = OF, overflow flag
+	 * 1<<10 = DF, direction flag
+	 */
+	static_assert(
+		((1<<0) | (1<<2) | (1<<4) | (1<<6) | (1<<7) | (1<<10) | (1<<11))
+		== 0xCD5
+	);
+
+	uint64_t newflags = (src->flags & 0xCD5) | (dst->flags & ~0xCD5);
+	/* I "spelled it out" directly instead of using memcpy hoping that gcc
+	 * maybe would notice it can skip copying the last 8 bytes. It didn't :( */
+	*dst = *src;
+	dst->flags = newflags;
+}
diff --git a/src/kernel/arch/amd64/sysenter.c b/src/kernel/arch/amd64/sysenter.c
index 5a96e33..2f83e3d 100644
--- a/src/kernel/arch/amd64/sysenter.c
+++ b/src/kernel/arch/amd64/sysenter.c
@@ -2,17 +2,20 @@
 #include <kernel/arch/amd64/sysenter.h>
 #include <kernel/arch/generic.h>
 #include <kernel/proc.h>
+#include <shared/mem.h>
 
-CpuRegs _sysexit_regs;
+SysexitRegs _sysexit_regs;
 
-_Noreturn void sysexit(CpuRegs regs) {
-	_sysexit_regs = regs;
+_Noreturn void sysexit(UserRegs *regs, char sse[512]) {
+	_sysexit_regs.u = *regs;
+	memcpy(_sysexit_regs.sse, sse, 512);
 	_sysexit_real();
 }
 
 _Noreturn void sysenter_stage2(void) {
-	CpuRegs *regs = &proc_cur->regs;
-	*regs = _sysexit_regs;
+	UserRegs *regs = &proc_cur->regs;
+	*regs = _sysexit_regs.u;
+	memcpy(proc_cur->sse, _sysexit_regs.sse, 512);
 	_syscall(regs->rdi, regs->rsi, regs->rdx, regs->r10, regs->r8, regs->r9);
 	proc_switch_any();
 }
diff --git a/src/kernel/arch/amd64/sysenter.h b/src/kernel/arch/amd64/sysenter.h
index 03a9f45..65c46f8 100644
--- a/src/kernel/arch/amd64/sysenter.h
+++ b/src/kernel/arch/amd64/sysenter.h
@@ -1,9 +1,14 @@
 #pragma once
 #include <kernel/types.h>
 
-// sysenter.c
-extern CpuRegs _sysexit_regs;
+typedef struct SysexitRegs SysexitRegs;
+struct SysexitRegs {
+	UserRegs u;
+	char sse[512];
+};
+_Static_assert(sizeof(SysexitRegs) == 18 * 8 + 512);
+
+extern SysexitRegs _sysexit_regs;
 _Noreturn void sysenter_stage2(void);
 
-// sysenter.s
 _Noreturn void _sysexit_real(void);
diff --git a/src/kernel/arch/generic.h b/src/kernel/arch/generic.h
index a6a14c9..c9431eb 100644
--- a/src/kernel/arch/generic.h
+++ b/src/kernel/arch/generic.h
@@ -27,8 +27,7 @@ uint64_t uptime_ns(void);
 void timer_schedule(Proc *p, uint64_t ns);
 void timer_deschedule(Proc *p);
 
-// src/arch/i386/sysenter.s
-_Noreturn void sysexit(CpuRegs);
+_Noreturn void sysexit(UserRegs *, char sse[512]);
 
 // all of those can allocate memory
 Pagedir *pagedir_new(void);
@@ -52,3 +51,7 @@ int kprintf(const char *fmt, ...);
 
 void *debug_caller(size_t depth);
 void debug_stacktrace(void);
+
+/** "Applies" an UserRegs struct received from userland over another UserRegs
+ * without overriding privileged registers. */
+void regs_safecopy(UserRegs *, const UserRegs *);