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cmd/internal/obj/arm: simplify huge frame prologue

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CL 307010 for arm.

Change-Id: I14d939eb8aa6f594927054a2595f8c270a0b607f
Reviewed-on: https://go-review.googlesource.com/c/go/+/307049
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
This commit is contained in:
Austin Clements 2021-04-02 16:59:22 -04:00
parent ef3122e909
commit 24dd8cfe23
2 changed files with 21 additions and 41 deletions
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4
src/cmd/internal/obj/arm/a.out.go
View File

@ -163,8 +163,8 @@ const (
C_SFCON
C_LFCON
C_RACON
C_LACON
C_RACON /* <=0xff rotated constant offset from auto */
C_LACON /* Large Auto CONstant, i.e. large offset from SP */
C_SBRA
C_LBRA

58
src/cmd/internal/obj/arm/obj5.go
View File

@ -680,57 +680,37 @@ func (c *ctxt5) stacksplit(p *obj.Prog, framesize int32) *obj.Prog {
p.From.Reg = REG_R1
p.Reg = REG_R2
} else {
// Such a large stack we need to protect against wraparound
// if SP is close to zero.
// SP-stackguard+StackGuard < framesize + (StackGuard-StackSmall)
// The +StackGuard on both sides is required to keep the left side positive:
// SP is allowed to be slightly below stackguard. See stack.h.
// CMP $StackPreempt, R1
// MOVW.NE $StackGuard(SP), R2
// SUB.NE R1, R2
// MOVW.NE $(framesize+(StackGuard-StackSmall)), R3
// CMP.NE R3, R2
p = obj.Appendp(p, c.newprog)
p.As = ACMP
p.From.Type = obj.TYPE_CONST
p.From.Offset = int64(uint32(objabi.StackPreempt & (1<<32 - 1)))
p.Reg = REG_R1
p = obj.Appendp(p, c.newprog)
p.As = AMOVW
p.From.Type = obj.TYPE_ADDR
p.From.Reg = REGSP
p.From.Offset = int64(objabi.StackGuard)
p.To.Type = obj.TYPE_REG
p.To.Reg = REG_R2
p.Scond = C_SCOND_NE
// Such a large stack we need to protect against underflow.
// The runtime guarantees SP > objabi.StackBig, but
// framesize is large enough that SP-framesize may
// underflow, causing a direct comparison with the
// stack guard to incorrectly succeed. We explicitly
// guard against underflow.
//
// // Try subtracting from SP and check for underflow.
// // If this underflows, it sets C to 0.
// SUB.S $(framesize-StackSmall), SP, R2
// // If C is 1 (unsigned >=), compare with guard.
// CMP.HS stackguard, R2
p = obj.Appendp(p, c.newprog)
p.As = ASUB
p.From.Type = obj.TYPE_REG
p.From.Reg = REG_R1
p.Scond = C_SBIT
p.From.Type = obj.TYPE_CONST
p.From.Offset = int64(framesize) - objabi.StackSmall
p.Reg = REGSP
p.To.Type = obj.TYPE_REG
p.To.Reg = REG_R2
p.Scond = C_SCOND_NE
p = obj.Appendp(p, c.newprog)
p.As = AMOVW
p.From.Type = obj.TYPE_ADDR
p.From.Offset = int64(framesize) + (int64(objabi.StackGuard) - objabi.StackSmall)
p.To.Type = obj.TYPE_REG
p.To.Reg = REG_R3
p.Scond = C_SCOND_NE
p = obj.Appendp(p, c.newprog)
p.As = ACMP
p.Scond = C_SCOND_HS
p.From.Type = obj.TYPE_REG
p.From.Reg = REG_R3
p.From.Reg = REG_R1
p.Reg = REG_R2
p.Scond = C_SCOND_NE
}
// BLS call-to-morestack
// BLS call-to-morestack (C is 0 or Z is 1)
bls := obj.Appendp(p, c.newprog)
bls.As = ABLS
bls.To.Type = obj.TYPE_BRANCH