cmd/asm: fix crash triggered by nested #define

A panic was in place for an impossible condition that turned
out to be possible if one used a macro to define a macro.

Another go-fuzz "win".

Fixes #12654.

Change-Id: I0a7bb0f0eabb260c986bf7a2288860c78d8db1af
Reviewed-on: https://go-review.googlesource.com/14777
Reviewed-by: Andrew Gerrand <adg@golang.org>

diff --git a/src/cmd/asm/internal/lex/lex_test.go b/src/cmd/asm/internal/lex/lex_test.go
index 14ffffecc812d2b38d2c5a04d9cbda8e8cf52c97..f606ffe07b06a0b1abe96cfa7f7b0521e0cea23b 100644 (file)
--- a/src/cmd/asm/internal/lex/lex_test.go
+++ b/src/cmd/asm/internal/lex/lex_test.go
@@ -226,6 +226,35 @@ var lexTests = []lexTest{
                ),
                "C.\n",
        },
+       {
+               "nested #define",
+               lines(
+                       "#define A #define B THIS",
+                       "A",
+                       "B",
+               ),
+               "THIS.\n",
+       },
+       {
+               "nested #define with args",
+               lines(
+                       "#define A #define B(x) x",
+                       "A",
+                       "B(THIS)",
+               ),
+               "THIS.\n",
+       },
+       /* This one fails. See comment in Slice.Col.
+       {
+               "nested #define with args",
+               lines(
+                       "#define A #define B (x) x",
+                       "A",
+                       "B(THIS)",
+               ),
+               "x.\n",
+       },
+       */
 }
 
 func TestLex(t *testing.T) {

diff --git a/src/cmd/asm/internal/lex/slice.go b/src/cmd/asm/internal/lex/slice.go
index e94106b0af5a34a196ce4aa7078368d83b0c253d..b0d5429e04ee70e67f1bfbd44f03d224f5493266 100644 (file)
--- a/src/cmd/asm/internal/lex/slice.go
+++ b/src/cmd/asm/internal/lex/slice.go
@@ -44,8 +44,16 @@ func (s *Slice) Line() int {
 }
 
 func (s *Slice) Col() int {
-       // Col is only called when defining a macro, which can't reach here.
-       panic("cannot happen: slice col")
+       // TODO: Col is only called when defining a macro and all it cares about is increasing
+       // position to discover whether there is a blank before the parenthesis.
+       // We only get here if defining a macro inside a macro.
+       // This imperfect implementation means we cannot tell the difference between
+       //      #define A #define B(x) x
+       // and
+       //      #define A #define B (x) x
+       // The first has definition of B has an argument, the second doesn't. Because we let
+       // text/scanner strip the blanks for us, this is extremely rare, hard to fix, and not worth it.
+       return s.pos
 }
 
 func (s *Slice) SetPos(line int, file string) {