From c91dffbc9aeaacd087eb0c0c3f718739bc5f8c4a Mon Sep 17 00:00:00 2001 From: Austin Clements Date: Wed, 7 Oct 2020 22:53:52 -0400 Subject: [PATCH] runtime: tidy cgocallback On amd64 and 386, we have a very roundabout way of remembering that we need to dropm on return that currently involves saving a zero to needm's argument slot and later bringing it back. Just store the zero. This also makes amd64 and 386 more consistent with cgocallback on all other platforms: rather than saving the old M to the G stack, they now save it to a named slot on the G0 stack. The needm function no longer needs a dummy argument to get the SP, so we drop that. Change-Id: I7e84bb4a5ff9552de70dcf41d8accf02310535e7 Reviewed-on: https://go-review.googlesource.com/c/go/+/263268 Trust: Austin Clements Run-TryBot: Austin Clements TryBot-Result: Go Bot Reviewed-by: Cherry Zhang --- src/runtime/asm_386.s | 18 +++++++----------- src/runtime/asm_amd64.s | 16 ++++++---------- src/runtime/proc.go | 6 +++--- src/runtime/signal_unix.go | 6 +++--- 4 files changed, 19 insertions(+), 27 deletions(-) diff --git a/src/runtime/asm_386.s b/src/runtime/asm_386.s index a54b68e03d..fa3b1be339 100644 --- a/src/runtime/asm_386.s +++ b/src/runtime/asm_386.s @@ -704,7 +704,7 @@ nosave: // cgocallback(fn, frame unsafe.Pointer, ctxt uintptr) // See cgocall.go for more details. -TEXT ·cgocallback(SB),NOSPLIT,$16-12 // Frame size must match commented places below +TEXT ·cgocallback(SB),NOSPLIT,$12-12 // Frame size must match commented places below NO_LOCAL_POINTERS // If g is nil, Go did not create the current thread. @@ -722,13 +722,12 @@ TEXT ·cgocallback(SB),NOSPLIT,$16-12 // Frame size must match commented places CMPL BP, $0 JEQ needm MOVL g_m(BP), BP - MOVL BP, DX // saved copy of oldm + MOVL BP, savedm-4(SP) // saved copy of oldm JMP havem needm: - MOVL $0, 0(SP) MOVL $runtime·needm(SB), AX CALL AX - MOVL 0(SP), DX + MOVL $0, savedm-4(SP) // dropm on return get_tls(CX) MOVL g(CX), BP MOVL g_m(BP), BP @@ -769,8 +768,6 @@ havem: // Once we switch to the curg stack, the pushed PC will appear // to be the return PC of cgocallback, so that the traceback // will seamlessly trace back into the earlier calls. - // - // In the new goroutine, 12(SP) holds the saved oldm (DX) register. MOVL m_curg(BP), SI MOVL SI, g(CX) MOVL (g_sched+gobuf_sp)(SI), DI // prepare stack as DI @@ -780,20 +777,18 @@ havem: MOVL fn+0(FP), AX MOVL frame+4(FP), BX MOVL ctxt+8(FP), CX - LEAL -(4+16)(DI), SP // Must match declared frame size - MOVL DX, 12(SP) + LEAL -(4+12)(DI), SP // Must match declared frame size MOVL AX, 0(SP) MOVL BX, 4(SP) MOVL CX, 8(SP) CALL runtime·cgocallbackg(SB) - MOVL 12(SP), DX // Restore g->sched (== m->curg->sched) from saved values. get_tls(CX) MOVL g(CX), SI - MOVL 16(SP), BP // Must match declared frame size + MOVL 12(SP), BP // Must match declared frame size MOVL BP, (g_sched+gobuf_pc)(SI) - LEAL (16+4)(SP), DI // Must match declared frame size + LEAL (12+4)(SP), DI // Must match declared frame size MOVL DI, (g_sched+gobuf_sp)(SI) // Switch back to m->g0's stack and restore m->g0->sched.sp. @@ -809,6 +804,7 @@ havem: // If the m on entry was nil, we called needm above to borrow an m // for the duration of the call. Since the call is over, return it with dropm. + MOVL savedm-4(SP), DX CMPL DX, $0 JNE 3(PC) MOVL $runtime·dropm(SB), AX diff --git a/src/runtime/asm_amd64.s b/src/runtime/asm_amd64.s index 3d5d9c4d58..19a3bb2d7d 100644 --- a/src/runtime/asm_amd64.s +++ b/src/runtime/asm_amd64.s @@ -693,7 +693,7 @@ nosave: // func cgocallback(fn, frame unsafe.Pointer, ctxt uintptr) // See cgocall.go for more details. -TEXT ·cgocallback(SB),NOSPLIT,$32-24 +TEXT ·cgocallback(SB),NOSPLIT,$24-24 NO_LOCAL_POINTERS // If g is nil, Go did not create the current thread. @@ -711,13 +711,12 @@ TEXT ·cgocallback(SB),NOSPLIT,$32-24 CMPQ BX, $0 JEQ needm MOVQ g_m(BX), BX - MOVQ BX, R8 // holds oldm until end of function + MOVQ BX, savedm-8(SP) // saved copy of oldm JMP havem needm: - MOVQ $0, 0(SP) - MOVQ $runtime·needm(SB), AX + MOVQ $runtime·needm(SB), AX CALL AX - MOVQ 0(SP), R8 + MOVQ $0, savedm-8(SP) // dropm on return get_tls(CX) MOVQ g(CX), BX MOVQ g_m(BX), BX @@ -758,8 +757,6 @@ havem: // Once we switch to the curg stack, the pushed PC will appear // to be the return PC of cgocallback, so that the traceback // will seamlessly trace back into the earlier calls. - // - // In the new goroutine, 24(SP) holds the saved R8. MOVQ m_curg(BX), SI MOVQ SI, g(CX) MOVQ (g_sched+gobuf_sp)(SI), DI // prepare stack as DI @@ -776,12 +773,10 @@ havem: SUBQ AX, DI // Allocate the same frame size on the g stack MOVQ DI, SP - MOVQ R8, 24(SP) MOVQ BX, 0(SP) MOVQ CX, 8(SP) MOVQ DX, 16(SP) CALL runtime·cgocallbackg(SB) - MOVQ 24(SP), R8 // Compute the size of the frame again. FP and SP have // completely different values here than they did above, @@ -811,7 +806,8 @@ havem: // If the m on entry was nil, we called needm above to borrow an m // for the duration of the call. Since the call is over, return it with dropm. - CMPQ R8, $0 + MOVQ savedm-8(SP), BX + CMPQ BX, $0 JNE 3(PC) MOVQ $runtime·dropm(SB), AX CALL AX diff --git a/src/runtime/proc.go b/src/runtime/proc.go index c629fd45f0..ec4e6d8751 100644 --- a/src/runtime/proc.go +++ b/src/runtime/proc.go @@ -1695,7 +1695,7 @@ func allocm(_p_ *p, fn func(), id int64) *m { // When the callback is done with the m, it calls dropm to // put the m back on the list. //go:nosplit -func needm(x byte) { +func needm() { if (iscgo || GOOS == "windows") && !cgoHasExtraM { // Can happen if C/C++ code calls Go from a global ctor. // Can also happen on Windows if a global ctor uses a @@ -1740,8 +1740,8 @@ func needm(x byte) { // which is more than enough for us. setg(mp.g0) _g_ := getg() - _g_.stack.hi = uintptr(noescape(unsafe.Pointer(&x))) + 1024 - _g_.stack.lo = uintptr(noescape(unsafe.Pointer(&x))) - 32*1024 + _g_.stack.hi = getcallersp() + 1024 + _g_.stack.lo = getcallersp() - 32*1024 _g_.stackguard0 = _g_.stack.lo + _StackGuard // Initialize this thread to use the m. diff --git a/src/runtime/signal_unix.go b/src/runtime/signal_unix.go index e8b6f95d8f..9318a9b8bc 100644 --- a/src/runtime/signal_unix.go +++ b/src/runtime/signal_unix.go @@ -504,14 +504,14 @@ func adjustSignalStack(sig uint32, mp *m, gsigStack *gsignalStack) bool { sigaltstack(nil, &st) if st.ss_flags&_SS_DISABLE != 0 { setg(nil) - needm(0) + needm() noSignalStack(sig) dropm() } stsp := uintptr(unsafe.Pointer(st.ss_sp)) if sp < stsp || sp >= stsp+st.ss_size { setg(nil) - needm(0) + needm() sigNotOnStack(sig) dropm() } @@ -951,7 +951,7 @@ func badsignal(sig uintptr, c *sigctxt) { exit(2) *(*uintptr)(unsafe.Pointer(uintptr(123))) = 2 } - needm(0) + needm() if !sigsend(uint32(sig)) { // A foreign thread received the signal sig, and the // Go code does not want to handle it.