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cmd/compile: don't devirtualize calls to runtime.memhash_varlen

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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>
This commit is contained in:
Michael Pratt 2023-11-16 14:58:37 -05:00
parent e62bf150cc
commit 3fd5c357a3
2 changed files with 14 additions and 0 deletions
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9
src/cmd/compile/internal/devirtualize/pgo.go
View File

@ -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:
//

5
src/runtime/stubs.go
View File

@ -374,6 +374,11 @@ func getcallersp() uintptr // implemented as an intrinsic on all platforms
//
// 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