runtime.memhash_varlen is defined as a normal function, but it is
actually a closure. All references are generated by
cmd/compile/internal/reflectdata.genhash, which creates a closure
containing the size of the type, which memhash_varlen accesses with
runtime.getclosureptr.
Since this doesn't look like a normal closure, ir.Func.OClosure is not
set, thus PGO function value devirtualization is willing to devirtualize
it, generating a call that completely ignores the closure context. This
causes memhash_varlen to either crash or generate incorrect results.
Skip this function, which is the only caller of getclosureptr.
Unfortunately there isn't a good way to detect these ineligible
functions more generally.
Fixes #64209.
Change-Id: Ibf509406667c6d4e5d431f10e5b1d1f926ecd7dc
Reviewed-on: https://go-review.googlesource.com/c/go/+/543195
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
}
return nil, nil, 0
}
+ // runtime.memhash_varlen does not look like a closure, but it uses
+ // runtime.getclosureptr to access data encoded by callers, which are
+ // are generated by cmd/compile/internal/reflectdata.genhash.
+ if callee.Sym().Pkg.Path == "runtime" && callee.Sym().Name == "memhash_varlen" {
+ if base.Debug.PGODebug >= 3 {
+ fmt.Printf("callee %s is a closure (runtime.memhash_varlen), skipping\n", ir.FuncName(callee))
+ }
+ return nil, nil, 0
+ }
// TODO(prattmic): We don't properly handle methods as callees in two
// different dimensions:
//
//
// The compiler rewrites calls to this function into instructions that fetch the
// pointer from a well-known register (DX on x86 architecture, etc.) directly.
+//
+// WARNING: PGO-based devirtualization cannot detect that caller of
+// getclosureptr require closure context, and thus must maintain a list of
+// these functions, which is in
+// cmd/compile/internal/devirtualize/pgo.maybeDevirtualizeFunctionCall.
func getclosureptr() uintptr
//go:noescape