Re: server.el test failures (was: Re: bug#9800: Incomplete truncated file buffers from the /proc filesystem)

[Jim Porter <jporterbugs@gmail.com>]

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On 2/23/2023 4:50 PM, Jim Porter wrote:
> Since the last message I posted, I'm now also seeing this test fail, 
> though I get a segfault instead. I bisected this to commit 
> a555abc56d5270cebe94f904189526d7ac433a94 ("Fix order of faces in 
> 'face-list'").
> 
> I'm pretty surprised by this, since that patch is *very* simple, but I 
> can reliably segfault with it, and never segfault without it. I'll keep 
> digging to see what's going on here.

The segfault is in FACE_FROM_ID_OR_NULL, called from 
Finternal_merge_in_global_face. It happens because the face_cache is 
null during these tests (since Emacs is noninteractive).

The attached patch fixes the issue for me, though I'm not totally sure 
it's the *right* fix. Any thoughts? (I'm also not 100% sure this is the 
same issue you're seeing...)

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From bcc1c44dcfaeab391cd85ec104ffa279f28409e4 Mon Sep 17 00:00:00 2001
From: Jim Porter <jporterbugs@gmail.com>
Date: Thu, 23 Feb 2023 18:16:28 -0800
Subject: [PATCH] Fix segmentation fault when merging faces in a noninteractive
 Emacs

* src/xfaces.c (internal-merge-in-global-face): Signal an error when
'noninteractive' is true.
---
 src/xfaces.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/xfaces.c b/src/xfaces.c
index 62d7823f308..0310d328b8f 100644
--- a/src/xfaces.c
+++ b/src/xfaces.c
@@ -4162,6 +4162,13 @@ DEFUN ("internal-merge-in-global-face", Finternal_merge_in_global_face,
   Lisp_Object global_lface, local_lface, *gvec, *lvec;
   struct frame *f = XFRAME (frame);
 
+  /* If this process is noninteractive, we likely don't have a face
+     cache, so attempts to use it below would segfault.  */
+  if (noninteractive)
+    {
+      error ("Attempt to merge faces in noninteractive Emacs");
+    }
+
   CHECK_LIVE_FRAME (frame);
   global_lface = lface_from_face_name (NULL, face, true);
   local_lface = lface_from_face_name (f, face, false);
-- 
2.25.1