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[dev.typeparams] Revert "[dev.typeparams] runtime,cmd/compile,cmd/link: replace jmpdefer with a loop"

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This reverts CL 227652.

I'm reverting CL 337651 and this builds on top of it.

Change-Id: I03ce363be44c2a3defff2e43e7b1aad83386820d
Reviewed-on: https://go-review.googlesource.com/c/go/+/338709
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
This commit is contained in:
Austin Clements 2021-07-30 16:40:17 -04:00
parent 40e561d933
commit e3e9f0bb2d
31 changed files with 324 additions and 39 deletions
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36
src/cmd/internal/obj/wasm/wasmobj.go
View file

@ -129,6 +129,8 @@ var (
morestackNoCtxt *obj.LSym
gcWriteBarrier *obj.LSym
sigpanic *obj.LSym
deferreturn *obj.LSym
jmpdefer *obj.LSym
)
const (
@ -141,6 +143,10 @@ func instinit(ctxt *obj.Link) {
morestackNoCtxt = ctxt.Lookup("runtime.morestack_noctxt")
gcWriteBarrier = ctxt.LookupABI("runtime.gcWriteBarrier", obj.ABIInternal)
sigpanic = ctxt.LookupABI("runtime.sigpanic", obj.ABIInternal)
deferreturn = ctxt.LookupABI("runtime.deferreturn", obj.ABIInternal)
// jmpdefer is defined in assembly as ABI0. The compiler will
// generate a direct ABI0 call from Go, so look for that.
jmpdefer = ctxt.LookupABI(`"".jmpdefer`, obj.ABI0)
}
func preprocess(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
@ -417,6 +423,12 @@ func preprocess(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
pcAfterCall-- // sigpanic expects to be called without advancing the pc
}
// jmpdefer manipulates the return address on the stack so deferreturn gets called repeatedly.
// Model this in WebAssembly with a loop.
if call.To.Sym == deferreturn {
p = appendp(p, ALoop)
}
// SP -= 8
p = appendp(p, AGet, regAddr(REG_SP))
p = appendp(p, AI32Const, constAddr(8))
@ -467,6 +479,15 @@ func preprocess(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
break
}
// jmpdefer removes the frame of deferreturn from the Go stack.
// However, its WebAssembly function still returns normally,
// so we need to return from deferreturn without removing its
// stack frame (no RET), because the frame is already gone.
if call.To.Sym == jmpdefer {
p = appendp(p, AReturn)
break
}
// return value of call is on the top of the stack, indicating whether to unwind the WebAssembly stack
if call.As == ACALLNORESUME && call.To.Sym != sigpanic { // sigpanic unwinds the stack, but it never resumes
// trying to unwind WebAssembly stack but call has no resume point, terminate with error
@ -479,6 +500,21 @@ func preprocess(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
unwindExitBranches = append(unwindExitBranches, p)
}
// jump to before the call if jmpdefer has reset the return address to the call's PC
if call.To.Sym == deferreturn {
// get PC_B from -8(SP)
p = appendp(p, AGet, regAddr(REG_SP))
p = appendp(p, AI32Const, constAddr(8))
p = appendp(p, AI32Sub)
p = appendp(p, AI32Load16U, constAddr(0))
p = appendp(p, ATee, regAddr(REG_PC_B))
p = appendp(p, AI32Const, constAddr(call.Pc))
p = appendp(p, AI32Eq)
p = appendp(p, ABrIf, constAddr(0))
p = appendp(p, AEnd) // end of Loop
}
case obj.ARET, ARETUNWIND:
ret := *p
p.As = obj.ANOP