GNU bug report logs - #34757
Invalid bytecode from byte compiler

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Message #17 received at 34757 <at> debbugs.gnu.org (full text, mbox):

From: Pip Cet <pipcet <at> gmail.com>
To: chuntaro <chuntaro <at> sakura-games.jp>
Cc: 34757 <at> debbugs.gnu.org
Subject: Re: bug#34757: Invalid bytecode from byte compiler
Date: Fri, 8 Mar 2019 21:13:37 +0000

[Message part 1 (text/plain, inline)]

On Tue, Mar 5, 2019 at 3:30 PM chuntaro <chuntaro <at> sakura-games.jp> wrote:
>
> Invalid bytecode is output and error occurs when executed.

If I'm looking at this correctly, the problem is that the byte code
which is generated in an intermediate step:

0       constant  2
1       constant  print
2       constant  1
3       call      1
4       discard
5       constant  3
6       return

is considered a "trivial function" by byte-compile-out-toplevel, which
assumes that all values on the stack are used by the call.

We could fix byte-compile-out-toplevel to properly analyze how many
stack arguments the call takes, but this patch simply treats forms
like this as nontrivial:

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index 0b8f8824b4c..4e54e08ce14 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -3025,6 +3025,7 @@ byte-compile-out-toplevel
                        (or (null (cdr rest))
                            (and (memq output-type '(file progn t))
                                 (cdr (cdr rest))
+                                (eql (length body) (cdr (car rest)))
                                 (eq (car (nth 1 rest)) 'byte-discard)
                                 (progn (setq rest (cdr rest)) t))))
                   (setq maycall nil)    ; Only allow one real function call.

[emacs-34757.diff (text/x-patch, attachment)]

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