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cmd/internal/obj/arm64: mark unsafe points

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For async preemption, we will be using REGTMP as a temporary
register in injected call on ARM64, which will clobber it. So any
code that uses REGTMP is not safe for async preemption.

In the assembler backend, we expand a Prog to multiple machine
instructions and use REGTMP as a temporary register if necessary.
These need to be marked unsafe. In fact, most of the
multi-instruction Progs use REGTMP, so we mark all of them,
except ones that are whitelisted.

Change-Id: I6e97805a13950e3b693fb606d77834940ac3722e
Reviewed-on: https://go-review.googlesource.com/c/go/+/203460
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Cherry Zhang 2019-10-21 14:08:11 -04:00
parent e5ce13c178
commit 4736088463
3 changed files with 106 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

47
src/cmd/internal/obj/arm64/asm7.go
View File

@ -258,8 +258,10 @@ func MOVCONST(d int64, s int, rt int) uint32 {
}
const (
LFROM = 1 << 0
LTO = 1 << 1
// Optab.flag
LFROM = 1 << 0 // p.From uses constant pool
LTO = 1 << 1 // p.To uses constant pool
NOTUSETMP = 1 << 2 // p expands to multiple instructions, but does NOT use REGTMP
)
var optab = []Optab{
@ -383,10 +385,10 @@ var optab = []Optab{
{AMOVD, C_MOVCON, C_NONE, C_NONE, C_REG, 32, 4, 0, 0, 0},
{AMOVW, C_BITCON, C_NONE, C_NONE, C_REG, 32, 4, 0, 0, 0},
{AMOVD, C_BITCON, C_NONE, C_NONE, C_REG, 32, 4, 0, 0, 0},
{AMOVW, C_MOVCON2, C_NONE, C_NONE, C_REG, 12, 8, 0, 0, 0},
{AMOVD, C_MOVCON2, C_NONE, C_NONE, C_REG, 12, 8, 0, 0, 0},
{AMOVD, C_MOVCON3, C_NONE, C_NONE, C_REG, 12, 12, 0, 0, 0},
{AMOVD, C_VCON, C_NONE, C_NONE, C_REG, 12, 16, 0, 0, 0},
{AMOVW, C_MOVCON2, C_NONE, C_NONE, C_REG, 12, 8, 0, NOTUSETMP, 0},
{AMOVD, C_MOVCON2, C_NONE, C_NONE, C_REG, 12, 8, 0, NOTUSETMP, 0},
{AMOVD, C_MOVCON3, C_NONE, C_NONE, C_REG, 12, 12, 0, NOTUSETMP, 0},
{AMOVD, C_VCON, C_NONE, C_NONE, C_REG, 12, 16, 0, NOTUSETMP, 0},
{AMOVK, C_VCON, C_NONE, C_NONE, C_REG, 33, 4, 0, 0, 0},
{AMOVD, C_AACON, C_NONE, C_NONE, C_REG, 4, 4, REGFROM, 0, 0},
@ -420,15 +422,15 @@ var optab = []Optab{
{ALSL, C_REG, C_REG, C_NONE, C_REG, 9, 4, 0, 0, 0},
{ASVC, C_VCON, C_NONE, C_NONE, C_NONE, 10, 4, 0, 0, 0},
{ASVC, C_NONE, C_NONE, C_NONE, C_NONE, 10, 4, 0, 0, 0},
{ADWORD, C_NONE, C_NONE, C_NONE, C_VCON, 11, 8, 0, 0, 0},
{ADWORD, C_NONE, C_NONE, C_NONE, C_LEXT, 11, 8, 0, 0, 0},
{ADWORD, C_NONE, C_NONE, C_NONE, C_ADDR, 11, 8, 0, 0, 0},
{ADWORD, C_NONE, C_NONE, C_NONE, C_LACON, 11, 8, 0, 0, 0},
{ADWORD, C_NONE, C_NONE, C_NONE, C_VCON, 11, 8, 0, NOTUSETMP, 0},
{ADWORD, C_NONE, C_NONE, C_NONE, C_LEXT, 11, 8, 0, NOTUSETMP, 0},
{ADWORD, C_NONE, C_NONE, C_NONE, C_ADDR, 11, 8, 0, NOTUSETMP, 0},
{ADWORD, C_NONE, C_NONE, C_NONE, C_LACON, 11, 8, 0, NOTUSETMP, 0},
{AWORD, C_NONE, C_NONE, C_NONE, C_LCON, 14, 4, 0, 0, 0},
{AWORD, C_NONE, C_NONE, C_NONE, C_LEXT, 14, 4, 0, 0, 0},
{AWORD, C_NONE, C_NONE, C_NONE, C_ADDR, 14, 4, 0, 0, 0},
{AMOVW, C_VCONADDR, C_NONE, C_NONE, C_REG, 68, 8, 0, 0, 0},
{AMOVD, C_VCONADDR, C_NONE, C_NONE, C_REG, 68, 8, 0, 0, 0},
{AMOVW, C_VCONADDR, C_NONE, C_NONE, C_REG, 68, 8, 0, NOTUSETMP, 0},
{AMOVD, C_VCONADDR, C_NONE, C_NONE, C_REG, 68, 8, 0, NOTUSETMP, 0},
{AMOVB, C_REG, C_NONE, C_NONE, C_ADDR, 64, 12, 0, 0, 0},
{AMOVBU, C_REG, C_NONE, C_NONE, C_ADDR, 64, 12, 0, 0, 0},
{AMOVH, C_REG, C_NONE, C_NONE, C_ADDR, 64, 12, 0, 0, 0},
@ -1022,6 +1024,23 @@ func span7(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
psz += 4
}
}
// Mark nonpreemptible instruction sequences.
// We use REGTMP as a scratch register during call injection,
// so instruction sequences that use REGTMP are unsafe to
// preempt asynchronously.
obj.MarkUnsafePoints(c.ctxt, c.cursym.Func.Text, c.newprog, c.isUnsafePoint)
}
// Return whether p is an unsafe point.
func (c *ctxt7) isUnsafePoint(p *obj.Prog) bool {
if p.From.Reg == REGTMP || p.To.Reg == REGTMP || p.Reg == REGTMP {
return true
}
// Most of the multi-instruction sequence uses REGTMP, except
// ones marked safe.
o := c.oplook(p)
return o.size > 4 && o.flag&NOTUSETMP == 0
}
/*
@ -3069,6 +3088,8 @@ func (c *ctxt7) asmout(p *obj.Prog, o *Optab, out []uint32) {
}
case 12: /* movT $vcon, reg */
// NOTE: this case does not use REGTMP. If it ever does,
// remove the NOTUSETMP flag in optab.
num := c.omovlconst(p.As, p, &p.From, int(p.To.Reg), os[:])
if num == 0 {
c.ctxt.Diag("invalid constant: %v", p)
@ -4017,6 +4038,8 @@ func (c *ctxt7) asmout(p *obj.Prog, o *Optab, out []uint32) {
o1 = c.opldpstp(p, o, v, uint32(r), uint32(p.From.Reg), uint32(p.From.Offset), 0)
case 68: /* movT $vconaddr(SB), reg -> adrp + add + reloc */
// NOTE: this case does not use REGTMP. If it ever does,
// remove the NOTUSETMP flag in optab.
if p.As == AMOVW {
c.ctxt.Diag("invalid load of 32-bit address: %v", p)
}

6
src/cmd/internal/obj/arm64/obj7.go
View File

@ -599,6 +599,10 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
// Store link register before decrementing SP, so if a signal comes
// during the execution of the function prologue, the traceback
// code will not see a half-updated stack frame.
// This sequence is not async preemptible, as if we open a frame
// at the current SP, it will clobber the saved LR.
q = c.ctxt.StartUnsafePoint(q, c.newprog)
q = obj.Appendp(q, c.newprog)
q.Pos = p.Pos
q.As = ASUB
@ -624,6 +628,8 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
q1.To.Type = obj.TYPE_REG
q1.To.Reg = REGSP
q1.Spadj = c.autosize
q1 = c.ctxt.EndUnsafePoint(q1, c.newprog, -1)
} else {
// small frame, update SP and save LR in a single MOVD.W instruction
q1 = obj.Appendp(q, c.newprog)

65
src/cmd/internal/obj/plist.go
View File

@ -206,3 +206,68 @@ func (ctxt *Link) EmitEntryLiveness(s *LSym, p *Prog, newprog ProgAlloc) *Prog {
return pcdata
}
// StartUnsafePoint generates PCDATA Progs after p to mark the
// beginning of an unsafe point. The unsafe point starts immediately
// after p.
// It returns the last Prog generated.
func (ctxt *Link) StartUnsafePoint(p *Prog, newprog ProgAlloc) *Prog {
pcdata := Appendp(p, newprog)
pcdata.As = APCDATA
pcdata.From.Type = TYPE_CONST
pcdata.From.Offset = objabi.PCDATA_StackMapIndex
pcdata.To.Type = TYPE_CONST
pcdata.To.Offset = -2 // pcdata -2 marks unsafe point
// TODO: register map?
return pcdata
}
// EndUnsafePoint generates PCDATA Progs after p to mark the end of an
// unsafe point, restoring the stack map index to oldval.
// The unsafe point ends right after p.
// It returns the last Prog generated.
func (ctxt *Link) EndUnsafePoint(p *Prog, newprog ProgAlloc, oldval int64) *Prog {
pcdata := Appendp(p, newprog)
pcdata.As = APCDATA
pcdata.From.Type = TYPE_CONST
pcdata.From.Offset = objabi.PCDATA_StackMapIndex
pcdata.To.Type = TYPE_CONST
pcdata.To.Offset = oldval
// TODO: register map?
return pcdata
}
// MarkUnsafePoints inserts PCDATAs to mark nonpreemptible instruction
// sequences, based on isUnsafePoint predicate. p0 is the start of the
// instruction stream.
func MarkUnsafePoints(ctxt *Link, p0 *Prog, newprog ProgAlloc, isUnsafePoint func(*Prog) bool) {
prev := p0
oldval := int64(-1) // entry pcdata
for p := prev.Link; p != nil; p, prev = p.Link, p {
if p.As == APCDATA && p.From.Offset == objabi.PCDATA_StackMapIndex {
oldval = p.To.Offset
continue
}
if oldval == -2 {
continue // already unsafe
}
if isUnsafePoint(p) {
q := ctxt.StartUnsafePoint(prev, newprog)
q.Pc = p.Pc
q.Link = p
// Advance to the end of unsafe point.
for p.Link != nil && isUnsafePoint(p.Link) {
p = p.Link
}
if p.Link == nil {
break // Reached the end, don't bother marking the end
}
p = ctxt.EndUnsafePoint(p, newprog, oldval)
p.Pc = p.Link.Pc
}
}
}