cmd/compile: fix panic in DWARF-gen handling obfuscated code

DWARF generation uses variable source positions (file/line/col) as a
way to uniquely identify locals and parameters, as part of the process
of matching up post-optimization variables with the corresponding
pre-optimization versions (since the DWARF needs to be in terms of the
original source constructs).

This strategy can run into problems when compiling obfuscated or
machine-generated code, where you can in some circumstances wind up
with two local variables that appear to have the same name, file,
line, and column. This patch changes DWARF generation to skip over
such duplicates as opposed to issuing a fatal error (if an
obfuscation tool is in use, it is unlikely that a human being will be
able to make much sense of DWARF info in any case).

Fixes #44378.

Change-Id: I198022d184701aa9ec3dce42c005d29b72d2e321
Reviewed-on: https://go-review.googlesource.com/c/go/+/294289
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Trust: Than McIntosh <thanm@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/cmd/compile/internal/dwarfgen/dwinl.go b/src/cmd/compile/internal/dwarfgen/dwinl.go
index d5687cb1d7..8adb36fc88 100644
--- a/src/cmd/compile/internal/dwarfgen/dwinl.go
+++ b/src/cmd/compile/internal/dwarfgen/dwinl.go
@@ -247,7 +247,8 @@ func makePreinlineDclMap(fnsym *obj.LSym) map[varPos]int {
 			DeclCol:  pos.Col(),
 		}
 		if _, found := m[vp]; found {
-			base.Fatalf("child dcl collision on symbol %s within %v\n", n.Sym().Name, fnsym.Name)
+			// We can see collisions (variables with the same name/file/line/col) in obfuscated or machine-generated code -- see issue 44378 for an example. Skip duplicates in such cases, since it is unlikely that a human will be debugging such code.
+			continue
 		}
 		m[vp] = i
 	}