runtime: allocate crash stack via stackalloc

On some platforms (notably OpenBSD), stacks must be specifically allocated
and marked as being stack memory. Allocate the crash stack using stackalloc,
which ensures these requirements are met, rather than using a global Go
variable.

Fixes #63794

Change-Id: I6513575797dd69ff0a36f3bfd4e5fc3bd95cbf50
Reviewed-on: https://go-review.googlesource.com/c/go/+/538457
Run-TryBot: Joel Sing <joel@sing.id.au>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Mauri de Souza Meneguzzo <mauri870@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index 408f26cf7a91531e3812a565d8ab922f12917be9..7189a0650ada59dcaa132e05ee9049c8785ab62e 100644 (file)
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -543,16 +543,9 @@ func badctxt() {
        throw("ctxt != 0")
 }
 
-// crashstack is a space that can be used as the stack when it is
-// crashing on bad stack conditions, e.g. morestack on g0.
-// gcrash is the corresponding (fake) g.
-var crashstack [16384]byte
-
-var gcrash = g{
-       stack:       stack{uintptr(unsafe.Pointer(&crashstack)), uintptr(unsafe.Pointer(&crashstack)) + unsafe.Sizeof(crashstack)},
-       stackguard0: uintptr(unsafe.Pointer(&crashstack)) + 1000,
-       stackguard1: uintptr(unsafe.Pointer(&crashstack)) + 1000,
-}
+// gcrash is a fake g that can be used when crashing due to bad
+// stack conditions.
+var gcrash g
 
 var crashingG atomic.Pointer[g]
 
@@ -803,6 +796,12 @@ func schedinit() {
        parsedebugvars()
        gcinit()
 
+       // Allocate stack space that can be used when crashing due to bad stack
+       // conditions, e.g. morestack on g0.
+       gcrash.stack = stackalloc(16384)
+       gcrash.stackguard0 = gcrash.stack.lo + 1000
+       gcrash.stackguard1 = gcrash.stack.lo + 1000
+
        // if disableMemoryProfiling is set, update MemProfileRate to 0 to turn off memprofile.
        // Note: parsedebugvars may update MemProfileRate, but when disableMemoryProfiling is
        // set to true by the linker, it means that nothing is consuming the profile, it is