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cmd/compile: panic: First time we've seen filename (part II) #35652

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ALTree opened this issue Nov 17, 2019 · 2 comments
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cmd/compile: panic: First time we've seen filename (part II) #35652

ALTree opened this issue Nov 17, 2019 · 2 comments
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FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. release-blocker
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Go1.14

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@ALTree
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ALTree commented Nov 17, 2019 

$ gotip version
go version devel +6ba0be1639 Sat Nov 16 20:31:45 2019 +0000 linux/amd64

The following code (minimized from a gosmith-generated program):

package p

func f() {
	for true {
		if true {
			continue
		}
	}
}

crashes the tip compiler with this error:

$ gotip build crash.go 

# command-line-arguments
panic: First time we've seen filename: "gofile..??"

goroutine 49 [running]:
cmd/internal/obj.(*Link).generateDebugLinesSymbol(0xc000378ea0, 0xc000553d00, 0xc000553f00)
	/home/alberto/go/src/cmd/internal/obj/dwarf.go:43 +0x8e3
cmd/internal/obj.(*Link).populateDWARF(0xc000378ea0, 0xe40dc0, 0xc000166160, 0xc000553d00, 0x7fff3ca56300, 0x16)
	/home/alberto/go/src/cmd/internal/obj/objfile.go:619 +0x31c
cmd/internal/obj.Flushplist(0xc000378ea0, 0xc00058bea8, 0xc000048250, 0x7fff3ca56300, 0x16)
	/home/alberto/go/src/cmd/internal/obj/plist.go:112 +0x7d8
cmd/compile/internal/gc.(*Progs).Flush(0xc00058c1c0)
	/home/alberto/go/src/cmd/compile/internal/gc/gsubr.go:94 +0xbc
cmd/compile/internal/gc.compileSSA(0xc000166160, 0x0)
	/home/alberto/go/src/cmd/compile/internal/gc/pgen.go:323 +0x690
cmd/compile/internal/gc.compileFunctions.func2(0xc000554d20, 0xc0005560f0, 0x0)
	/home/alberto/go/src/cmd/compile/internal/gc/pgen.go:363 +0x49
created by cmd/compile/internal/gc.compileFunctions
	/home/alberto/go/src/cmd/compile/internal/gc/pgen.go:361 +0x128

It compiles fine on Go1.13.4.

This appears to be related to the compiler crash previously reported in #34520.

cc @cherrymui @aclements @randall77
@ALTree ALTree added NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. release-blocker labels Nov 17, 2019
@ALTree ALTree added this to the Go1.14 milestone Nov 17, 2019
@dr2chase dr2chase self-assigned this Nov 18, 2019
@gopherbot
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Change https://golang.org/cl/207613 mentions this issue: cmd/compile: make a better bogus line for empty infinite loops

@ALTree ALTree mentioned this issue Nov 19, 2019
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@gopherbot
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Change https://golang.org/cl/207964 mentions this issue: cmd/compile: try harder to not use an empty src.XPos for a bogus line

gopherbot pushed a commit that referenced this issue Nov 22, 2019
@dr2chase
cmd/compile: try harder to not use an empty src.XPos for a bogus line
0e02cfb 
The fix for #35652 did not guarantee that it was using a non-empty
src position to replace an empty one.  The new code checks again
and falls back to a more certain position.  (The input in question
compiles to a single empty infinite loop, and none of the actual instructions
had any source position at all.  That is a bug, but given the pathology
of this input, not one worth dealing with this late in the release cycle,
if ever.)

Literally:

00000 (5) TEXT "".f(SB), ABIInternal
00001 (5) PCDATA $0, $-2
00002 (5) PCDATA $1, $-2
00003 (5) FUNCDATA $0, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
00004 (5) FUNCDATA $1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
00005 (5) FUNCDATA $2, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)
b2
00006 (?) XCHGL AX, AX
b6
00007 (+1048575) JMP 6
00008 (?) END

TODO: Add runtime.InfiniteLoop(), replace infinite loops with a call to
that, and use an eco-friendly runtime.gopark instead.  (This was Cherry's
excellent idea.)

Updates #35652
Fixes #35695

Change-Id: I4b9a841142ee4df0f6b10863cfa0721a7e13b437
Reviewed-on: https://go-review.googlesource.com/c/go/+/207964
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
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