From 3fd5c357a3a763f70f3ed684caed878e732e6ebe Mon Sep 17 00:00:00 2001 From: Michael Pratt Date: Thu, 16 Nov 2023 14:58:37 -0500 Subject: cmd/compile: don't devirtualize calls to runtime.memhash_varlen 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 LUCI-TryBot-Result: Go LUCI --- src/cmd/compile/internal/devirtualize/pgo.go | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'src/cmd') diff --git a/src/cmd/compile/internal/devirtualize/pgo.go b/src/cmd/compile/internal/devirtualize/pgo.go index 0a34e7eb8d..7b6c8ba0c0 100644 --- a/src/cmd/compile/internal/devirtualize/pgo.go +++ b/src/cmd/compile/internal/devirtualize/pgo.go @@ -241,6 +241,15 @@ func maybeDevirtualizeFunctionCall(p *pgo.Profile, fn *ir.Func, call *ir.CallExp } 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: // -- cgit v1.3-5-g9baa