From 6bd37418a378bec4916ad70403375af00df91938 Mon Sep 17 00:00:00 2001 From: Ian Lance Taylor Date: Tue, 19 Feb 2019 15:32:34 +0000 Subject: [PATCH] runtime: abort stack scan in cases that we cannot unwind the stack In signal-triggered stack scan, if the signal is delivered at certain bad time (e.g. in vdso, or in the middle of setcontext?), the unwinder may not be able to unwind the whole stack, while it still reports _URC_END_OF_STACK. So we cannot rely on _URC_END_OF_STACK to tell if it successfully scanned the stack. Instead, we check the last Go frame to see it actually reached the end of the stack. For Go-created stack, this is runtime.kickoff. For C-created stack, we need to record the outermost Go frame when it enters the Go side. Also we cannot unwind the stack if the signal is delivered in the middle of runtime.gogo, halfway through a goroutine switch, where the g and the stack don't match. Give up in this case as well. Reviewed-on: https://go-review.googlesource.com/c/159098 From-SVN: r269018 --- gcc/go/gofrontend/MERGE | 2 +- libgo/go/runtime/cgo_gccgo.go | 4 +++ libgo/go/runtime/proc.go | 3 ++ libgo/go/runtime/runtime2.go | 1 + libgo/go/runtime/stubs.go | 4 +++ libgo/runtime/go-unwind.c | 62 ++++++++++++++++++++++++++--------- 6 files changed, 59 insertions(+), 17 deletions(-) diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE index d9ee0bad869..07437d4809c 100644 --- a/gcc/go/gofrontend/MERGE +++ b/gcc/go/gofrontend/MERGE @@ -1,4 +1,4 @@ -9605c2efd99aa9c744652a9153e208e0653b8596 +672572130ba7a7b277a4c9c8f93576fc42accf63 The first line of this file holds the git revision number of the last merge done from the gofrontend repository. diff --git a/libgo/go/runtime/cgo_gccgo.go b/libgo/go/runtime/cgo_gccgo.go index aff8130a27c..e4d27e8ab67 100644 --- a/libgo/go/runtime/cgo_gccgo.go +++ b/libgo/go/runtime/cgo_gccgo.go @@ -80,6 +80,10 @@ func CgocallBack() { gp = getg() mp := gp.m mp.dropextram = true + + // This is a C-created stack. + // Record the outermost Go frame to help stack scan. + gp.entrysp = getcallersp() } lockOSThread() diff --git a/libgo/go/runtime/proc.go b/libgo/go/runtime/proc.go index e9375635b3e..1c944d64752 100644 --- a/libgo/go/runtime/proc.go +++ b/libgo/go/runtime/proc.go @@ -1192,6 +1192,9 @@ func kickoff() { gp.param = nil } + // Record the entry SP to help stack scan. + gp.entrysp = getsp() + fv(param) goexit1() } diff --git a/libgo/go/runtime/runtime2.go b/libgo/go/runtime/runtime2.go index 4cd68da2ea2..4f823e09b4b 100644 --- a/libgo/go/runtime/runtime2.go +++ b/libgo/go/runtime/runtime2.go @@ -433,6 +433,7 @@ type g struct { entry func(unsafe.Pointer) // goroutine function to run entryfn uintptr // function address passed to __go_go + entrysp uintptr // the stack pointer of the outermost Go frame fromgogo bool // whether entered from gogo function scanningself bool // whether goroutine is scanning its own stack diff --git a/libgo/go/runtime/stubs.go b/libgo/go/runtime/stubs.go index 9f5191bc661..dfdb38e8010 100644 --- a/libgo/go/runtime/stubs.go +++ b/libgo/go/runtime/stubs.go @@ -231,6 +231,10 @@ func getcallerpc() uintptr //go:noescape func getcallersp() uintptr // implemented as an intrinsic on all platforms +// getsp returns the stack pointer (SP) of the caller of getsp. +//go:noinline +func getsp() uintptr { return getcallersp() } + func asmcgocall(fn, arg unsafe.Pointer) int32 { throw("asmcgocall") return 0 diff --git a/libgo/runtime/go-unwind.c b/libgo/runtime/go-unwind.c index 158cbd07968..9fd9596926a 100644 --- a/libgo/runtime/go-unwind.c +++ b/libgo/runtime/go-unwind.c @@ -649,6 +649,19 @@ findstackmaps (struct _Unwind_Context *context, _Unwind_Ptr *ip, _Unwind_Ptr *sp _sleb128_t index; int size; +#ifdef HAVE_GETIPINFO + ip1 = _Unwind_GetIPInfo (context, &ip_before_insn); +#else + ip1 = _Unwind_GetIP (context); +#endif + if (! ip_before_insn) + --ip1; + + if (ip != NULL) + *ip = ip1; + if (sp != NULL) + *sp = _Unwind_GetCFA (context); + #ifdef __ARM_EABI_UNWINDER__ { _Unwind_Control_Block *ucbp; @@ -672,14 +685,6 @@ findstackmaps (struct _Unwind_Context *context, _Unwind_Ptr *ip, _Unwind_Ptr *sp if (info.TType == NULL) return NOTFOUND_OK; -#ifdef HAVE_GETIPINFO - ip1 = _Unwind_GetIPInfo (context, &ip_before_insn); -#else - ip1 = _Unwind_GetIP (context); -#endif - if (! ip_before_insn) - --ip1; - size = value_size (info.ttype_encoding); action_record = NULL; @@ -738,15 +743,16 @@ findstackmaps (struct _Unwind_Context *context, _Unwind_Ptr *ip, _Unwind_Ptr *sp if (stackmap1 == NULL) return NOTFOUND_BAD; - if (ip != NULL) - *ip = ip1; - if (sp != NULL) - *sp = _Unwind_GetCFA (context); if (stackmap != NULL) *stackmap = stackmap1; return FOUND; } +struct scanstate { + void* gcw; // the GC worker, passed into scanstackwithmap_callback + uintptr lastsp; // the last (outermost) SP of Go function seen in a traceback, set by the callback +}; + // Callback function to scan a stack frame with stack maps. // It skips non-Go functions. static _Unwind_Reason_Code @@ -755,7 +761,11 @@ scanstackwithmap_callback (struct _Unwind_Context *context, void *arg) struct _stackmap *stackmap; _Unwind_Ptr ip, sp; G* gp; - void *gcw = arg; + struct scanstate* state = (struct scanstate*) arg; + void *gcw; + + gp = runtime_g (); + gcw = state->gcw; switch (findstackmaps (context, &ip, &sp, &stackmap)) { @@ -767,7 +777,6 @@ scanstackwithmap_callback (struct _Unwind_Context *context, void *arg) // No stack map found. // If we're scanning from the signal stack, the goroutine // may be not stopped at a safepoint. Allow this case. - gp = runtime_g (); if (gp != gp->m->gsignal) { // TODO: print gp, pc, sp @@ -781,6 +790,7 @@ scanstackwithmap_callback (struct _Unwind_Context *context, void *arg) abort (); } + state->lastsp = sp; runtime_scanstackblockwithmap (ip, sp, (uintptr)(stackmap->len) * sizeof(uintptr), stackmap->data, gcw); return _URC_NO_REASON; @@ -792,10 +802,30 @@ bool scanstackwithmap (void *gcw) { _Unwind_Reason_Code code; + bool ret; + struct scanstate state; + G* gp; + G* curg; + + state.gcw = gcw; + state.lastsp = 0; + gp = runtime_g (); + curg = gp->m->curg; + runtime_xadd (&__go_runtime_in_callers, 1); - code = _Unwind_Backtrace (scanstackwithmap_callback, gcw); + code = _Unwind_Backtrace (scanstackwithmap_callback, (void*)&state); runtime_xadd (&__go_runtime_in_callers, -1); - return code == _URC_END_OF_STACK; + ret = (code == _URC_END_OF_STACK); + if (ret && gp == gp->m->gsignal) + { + // For signal-triggered scan, the unwinder may not be able to unwind + // the whole stack while it still reports _URC_END_OF_STACK (e.g. + // signal is delivered in vdso). Check that we actually reached the + // the end of the stack, that is, the SP on entry. + if (state.lastsp != curg->entrysp) + ret = false; + } + return ret; } // Returns whether stack map is enabled.