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cmd/internal/obj/x86: add comments to wrapper prologue insertion

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Make the comments a bit clearer and more accurate,
in anticipation of updating the code.

Change-Id: I1111e6c3405a8688fcd29b809a48a762ff41edaa
Reviewed-on: https://go-review.googlesource.com/36833
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Josh Bleecher Snyder 2017-02-10 14:56:05 -08:00
parent 2c91bb4c8a
commit 5030bfdf81
1 changed files with 14 additions and 3 deletions
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17
src/cmd/internal/obj/x86/obj6.go
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@ -742,7 +742,9 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
}
if cursym.Text.From3Offset()&obj.WRAPPER != 0 {
// if(g->panic != nil && g->panic->argp == FP) g->panic->argp = bottom-of-frame
// if g._panic != nil && g._panic.argp == FP {
// g._panic.argp = bottom-of-frame
// }
//
// MOVQ g_panic(CX), BX
// TESTQ BX, BX
@ -757,12 +759,12 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
// The NOP is needed to give the jumps somewhere to land.
// It is a liblink NOP, not an x86 NOP: it encodes to 0 instruction bytes.
// MOVQ g_panic(CX), BX
p = obj.Appendp(ctxt, p)
p.As = AMOVQ
p.From.Type = obj.TYPE_MEM
p.From.Reg = REG_CX
p.From.Offset = 4 * int64(ctxt.Arch.PtrSize) // G.panic
p.From.Offset = 4 * int64(ctxt.Arch.PtrSize) // g_panic
p.To.Type = obj.TYPE_REG
p.To.Reg = REG_BX
if ctxt.Headtype == obj.Hnacl && p.Mode == 64 {
@ -776,6 +778,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
p.As = AMOVL
}
// TESTQ BX, BX
p = obj.Appendp(ctxt, p)
p.As = ATESTQ
p.From.Type = obj.TYPE_REG
@ -786,11 +789,13 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
p.As = ATESTL
}
// JEQ end
p = obj.Appendp(ctxt, p)
p.As = AJEQ
p.To.Type = obj.TYPE_BRANCH
p1 := p
// LEAQ (autoffset+8)(SP), DI
p = obj.Appendp(ctxt, p)
p.As = ALEAQ
p.From.Type = obj.TYPE_MEM
@ -802,6 +807,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
p.As = ALEAL
}
// CMPQ panic_argp(BX), DI
p = obj.Appendp(ctxt, p)
p.As = ACMPQ
p.From.Type = obj.TYPE_MEM
@ -820,11 +826,13 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
p.As = ACMPL
}
// JNE end
p = obj.Appendp(ctxt, p)
p.As = AJNE
p.To.Type = obj.TYPE_BRANCH
p2 := p
// MOVQ SP, panic_argp(BX)
p = obj.Appendp(ctxt, p)
p.As = AMOVQ
p.From.Type = obj.TYPE_REG
@ -843,8 +851,11 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
p.As = AMOVL
}
// NOP
p = obj.Appendp(ctxt, p)
p.As = obj.ANOP
// Set targets for jumps above to the NOP
p1.Pcond = p
p2.Pcond = p
}