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runtime: pcdata is -2 and 12 locals stack map entries error on nil pointer [1.14 backport] #40647

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gopherbot opened this issue Aug 8, 2020 · 3 comments

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@gopherbot
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@gopherbot gopherbot commented Aug 8, 2020

@randall77 requested issue #40629 to be considered for backport to the next 1.14 minor release.

This patch:

+++ b/src/cmd/compile/internal/ssa/func.go
@@ -274,6 +274,9 @@ func (f *Func) freeValue(v *Value) {
        if len(v.Args) != 0 {
                f.Fatalf("value %s still has %d args", v, len(v.Args))
        }
+       if v == f.LastDeferExit {
+               println("FREEING THE LASTDEFEREXIT")
+       }
        // Clear everything but ID (which we reuse).
        id := v.ID

triggers a bunch of times during make.bash. Both 1.14.2 and tip. Looks like we need to fix this for the release - I think we're just getting lucky that we don't stack copy or gc trace such cases normally (stack copy is only likely to happen with an unrecovered panic?), or that the random other instruction's liveness map is correct (or good enough).

@gopherbot please open a backport issue for 1.14.

1.13 is ok, as open-coded defers were released for 1.14.

@gopherbot
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@gopherbot gopherbot commented Aug 14, 2020

Change https://golang.org/cl/248622 mentions this issue: cmd/compile: fix live variable computation for deferreturn

@dmitshur dmitshur modified the milestones: Go1.14.8, Go1.14.9 Sep 1, 2020
@dmitshur dmitshur modified the milestones: Go1.14.9, Go1.14.10 Sep 9, 2020
@toothrot
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@toothrot toothrot commented Sep 11, 2020

Approved. This is a serious issue with no workaround.

gopherbot pushed a commit that referenced this issue Oct 5, 2020
…r deferreturn

Taking the live variable set from the last return point is problematic.
See #40629 for details, but there may not be a return point, or it may
be before the final defer.

Additionally, keeping track of the last call as a *Value doesn't quite
work. If it is dead-code eliminated, the storage for the Value is reused
for some other random instruction. Its live variable information,
if it is available at all, is wrong.

Instead, just mark all the open-defer argument slots as live
throughout the function. (They are already zero-initialized.)

Fixes #40647

Change-Id: Ie456c7db3082d0de57eaa5234a0f32525a1cce13
Reviewed-on: https://go-review.googlesource.com/c/go/+/247522
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>
(cherry picked from commit 32a84c9)
Reviewed-on: https://go-review.googlesource.com/c/go/+/248622
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Dmitri Shuralyov <dmitshur@golang.org>
@gopherbot
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@gopherbot gopherbot commented Oct 5, 2020

Closed by merging a4af75d to release-branch.go1.14.

@gopherbot gopherbot closed this Oct 5, 2020
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