ref: 20b7a19c58c79568424bf40b826b681af86e6ed5
parent: b6039915934ec99e85daa5d4ee964dbda3503352
author: cinap_lenrek <[email protected]>
date: Sun Jul 20 18:49:02 EDT 2014
pc64: preserve user extern registers R14 and R15 across syscalls, use Ureg.bp (RARG) for syscall number the 6c compiler reserves R14 and R15 for extern register variables, which is used by the kernel to hold the m and up pointers. until now, the meaning of R14 and R15 was undefined for userspace and extern register would not work as the kernel trashes R14 and R15 on syscalls. with this change, user extern registers R14 and R15 are zeroed on exec and otherwise preserved across syscalls. so userspace *could* use them for per process variables like the kernel does. use Ureg.bp (RARG) for syscall number instead of Ureg.ax. this is less confusing and mirrors the amd64 calling convention.
--- a/sys/src/9/pc64/l.s
+++ b/sys/src/9/pc64/l.s
@@ -686,15 +686,20 @@
TEXT touser(SB), 1, $-4
CLI
SWAPGS
- MOVQ $UDSEL, AX
+
+ MOVW $UDSEL, AX
MOVW AX, DS
MOVW AX, ES
+
+ MOVW $NULLSEL, AX
MOVW AX, FS
MOVW AX, GS
- MOVQ $(UTZERO+0x28), CX /* ip */
- MOVQ $0x200, R11 /* flags */
+ MOVL $0, RMACH
+ MOVL $0, RUSER
+ MOVQ $(UTZERO+0x28), CX /* ip */
+ MOVL $0x200, R11 /* flags */
MOVQ RARG, SP /* sp */
BYTE $0x48; SYSRET /* SYSRETQ */
@@ -703,11 +708,12 @@
*/
TEXT syscallentry(SB), 1, $-4
SWAPGS
- BYTE $0x65; MOVQ 0, RMACH /* m-> (MOVQ GS:0x0, R15) */
- MOVQ 16(RMACH), RUSER /* m->proc */
+ BYTE $0x65; MOVQ 0, AX /* m-> (MOVQ GS:0x0, AX) */
+ MOVQ 16(AX), BX /* m->proc */
MOVQ SP, R13
- MOVQ 16(RUSER), SP /* m->proc->kstack */
+ MOVQ 16(BX), SP /* m->proc->kstack */
ADDQ $KSTACK, SP
+
PUSHQ $UDSEL /* old stack segment */
PUSHQ R13 /* old sp */
PUSHQ R11 /* old flags */
@@ -714,8 +720,7 @@
PUSHQ $UESEL /* old code segment */
PUSHQ CX /* old ip */
- SUBQ $(17*8), SP /* unsaved registers */
- PUSHQ RARG /* system call number */
+ SUBQ $(16+16*8), SP /* unsaved registers */
MOVW $UDSEL, (15*8+0)(SP)
MOVW ES, (15*8+2)(SP)
@@ -722,26 +727,36 @@
MOVW FS, (15*8+4)(SP)
MOVW GS, (15*8+6)(SP)
+ MOVQ RMACH, (14*8)(SP)
+ MOVQ RUSER, (13*8)(SP)
+
+ MOVQ RARG, (6*8)(SP) /* system call number */
+
+ MOVQ AX, RMACH /* m */
+ MOVQ BX, RUSER /* up */
+
MOVQ SP, RARG
- PUSHQ SP /* Ureg* */
+ PUSHQ SP
CALL syscall(SB)
TEXT forkret(SB), 1, $-4
- MOVQ 8(SP), AX /* Ureg.ax */
- MOVQ (8+6*8)(SP), BP /* Ureg.bp */
- ADDQ $(16*8), SP /* registers + arguments */
+ MOVQ 8(SP), AX
+ ADDQ $(8+13*8), SP /* unsaved registers */
CLI
SWAPGS
- MOVW 0(SP), DS
- MOVW 2(SP), ES
- MOVW 4(SP), FS
- MOVW 6(SP), GS
- MOVQ 24(SP), CX /* ip */
- MOVQ 40(SP), R11 /* flags */
+ MOVW 22(SP), GS
+ MOVW 20(SP), FS
+ MOVW 18(SP), ES
+ MOVW 16(SP), DS
- MOVQ 48(SP), SP /* sp */
+ MOVQ 8(SP), RMACH
+ MOVQ 0(SP), RUSER
+
+ MOVQ 40(SP), CX /* ip */
+ MOVQ 56(SP), R11 /* flags */
+ MOVQ 64(SP), SP /* sp */
BYTE $0x48; SYSRET /* SYSRETQ */
--- a/sys/src/9/pc64/trap.c
+++ b/sys/src/9/pc64/trap.c
@@ -686,7 +686,7 @@
up->dbgreg = ureg;
sp = ureg->sp;
- scallnr = ureg->ax;
+ scallnr = ureg->bp; /* RARG */
up->scallnr = scallnr;
spllo();
@@ -735,13 +735,6 @@
up->errlab[i].sp, up->errlab[i].pc);
panic("error stack");}
-
- /*
- * Put return value in frame. On the x86 the syscall is
- * just another trap and the return value from syscall is
- * ignored. On other machines the return value is put into
- * the results register by caller of syscall.
- */
ureg->ax = ret;
if(0){@@ -902,13 +895,9 @@
pexit("Suicide", 0);}
- /* don't let user change system flags */
- nureg->flags = (ureg->flags & ~0xCD5) | (nureg->flags & 0xCD5);
- nureg->cs |= 3;
- nureg->ss |= 3;
+ /* don't let user change system flags or segment registers */
+ setregisters(ureg, (char*)ureg, (char*)nureg, sizeof(Ureg));
- memmove(ureg, nureg, sizeof(Ureg));
-
switch(arg0){case NCONT:
case NRSTR:
@@ -965,6 +954,7 @@
ureg->cs = UESEL;
ureg->ss = ureg->ds = ureg->es = UDSEL;
ureg->fs = ureg->gs = NULLSEL;
+ ureg->r14 = ureg->r15 = 0; /* extern user registers */
return (uintptr)USTKTOP-sizeof(Tos); /* address of kernel/user shared data */
}
@@ -981,7 +971,7 @@
}
/* This routine must save the values of registers the user is not permitted
- * to write from devproc and then restore the saved values before returning.
+ * to write from devproc and noted() and then restore the saved values before returning.
*/
void
setregisters(Ureg* ureg, char* pureg, char* uva, int n)
@@ -995,7 +985,7 @@
if(ureg->fs != UDSEL)
ureg->fs = NULLSEL;
if(ureg->gs != UDSEL)
- ureg->gs = 0;
+ ureg->gs = NULLSEL;
ureg->flags = (ureg->flags & 0x00ff) | (flags & 0xff00);
ureg->pc &= UADDRMASK;
}
@@ -1063,8 +1053,7 @@
Ureg *ureg;
ureg = p->dbgreg;
- if(ureg == 0)
+ if(ureg == nil)
return 0;
-
return ureg->pc;
}