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Groups > linux.debian.kernel > #90559
| From | Gianluca Renzi <gianlucarenzi@eurek.it> |
|---|---|
| Newsgroups | linux.debian.kernel |
| Subject | Re: Weird characters in virtual terminal consoles from (CTRL-ALT) F2 to F6 and over F7 |
| Date | 2025-12-22 12:20 +0100 |
| Message-ID | <M4M7g-4OBu-11@gated-at.bofh.it> (permalink) |
| References | <M4DGF-4Isq-3@gated-at.bofh.it> <M4L1v-4NSv-5@gated-at.bofh.it> <M4L1v-4NSv-3@gated-at.bofh.it> <M4M7g-4OBu-13@gated-at.bofh.it> |
| Organization | Eurek S.R.L. |
On 12/22/25 11:13, Helge Deller wrote:
> On 12/22/25 11:09, Gianluca Renzi wrote:
>> Wow! So you found the culprit.
>
> Well, it seems pretty likely that you get the "copyright symbol",
> because ch gets assigned "0". The question is: Why does this happen?
> It shouldn't.
>
> Does it only happens with old kernels (5.x), or does it happen with
> latest
> Linux kernels (>= 6.8) too?
>
The issue is not present with the kernel 5.10.0-36-amd64, only in kernel
5.10.0-37-amd64 (5.10.247-1)
I have a couple of Debian 12 machines laying around, and this bug is not
present for sure.
I do not remember which kernel they can have, but it's the stable Debian
12 version.
> Helge
>
>> From Wednesday I will be on Christmas holidays, so I can help if needed
>>
>> Ciao e buona giornata.
>>
>> "GP! In mezzo al campo stai proprio schifoso!"
>> Coach M.Russo
>>
>> Il lun 22 dic 2025, 11:00 Helge Deller <deller@kernel.org
>> <mailto:deller@kernel.org>> ha scritto:
>>
>> * William Burrow <wbkernel@gmail.com <mailto:wbkernel@gmail.com>>:
>> > Hello, Camaleón and Salvatore.
>> > I have a similar problem with the TTYs and am very glad to
>> have found
>> > this message. Hopefully, my reply can make it to the list.
>> > .
>> > The offending commit was fairly easy to find as will be detailed
>> > later. The git bisect on the linux-stable repo found the
>> following
>> > commit as the problem:
>> > .
>> > ------------ First commit to cause the problem ------------
>> > commit 0998a6cb232674408a03e8561dc15aa266b2f53b
>> > Author: Junjie Cao <junjie.cao@intel.com
>> <mailto:junjie.cao@intel.com>>
>> > Date: Mon Oct 20 21:47:01 2025 +0800
>> >
>> > fbdev: bitblit: bound-check glyph index in bit_putcs*
>> >
>> > commit 18c4ef4e765a798b47980555ed665d78b71aeadf upstream.
>> > ------------ First commit to cause the problem ------------
>> > .
>> > I leave it as an exercise to the reader to solve the problem
>> created
>> > by this commit. Hopefully, soon.
>>
>> Can someone please try attached patch?
>> Alternatively (if then another char that the "copyright symbol" is
>> visible), we could try replacing it by:
>> ch = 0x20; /* use ASCII space character */
>>
>> Overall, I'm still puzzled if the original patch is correct.
>> I always thought fonts have 256 or 512 characters, which means the
>> original patch isn't necessary at all.
>>
>> Helge
>>
>>
>> >From 65c6bb3e7d06dba09f6b529a2478ee818c14e6ef Mon Sep 17
>> 00:00:00 2001
>> From: Helge Deller <deller@gmx.de <mailto:deller@gmx.de>>
>> Date: Mon, 22 Dec 2025 10:19:55 +0100
>> Subject: [PATCH] fbdev: bitblit: fix bound-check of glyph index
>> in bit_putcs*
>>
>> The patch 18c4ef4e765a ("fbdev: bitblit: bound-check glyph index in
>> bit_putcs*") seems to trigger problems on virtual consoles, which
>> suddently show up with lots of copyright symbols. This is e.g.
>> reported
>> here:
>> https://www.reddit.com/r/debian/comments/1pnrm5t/problem_with_virtual_consoles_covered_with_a/
>> <https://www.reddit.com/r/debian/comments/1pnrm5t/problem_with_virtual_consoles_covered_with_a/>
>>
>>
>> Try to narrow the issue down. Here we use the "last" char of a given
>> font (instead of char #0), if the previous char exceeds the actual
>> font's glyph count.
>>
>> Reported-by: Gianluca Renzi <gianlucarenzi@eurek.it
>> <mailto:gianlucarenzi@eurek.it>>
>> Signed-off-by: Helge Deller <deller@gmx.de <mailto:deller@gmx.de>>
>> Fixes: 18c4ef4e765a ("fbdev: bitblit: bound-check glyph index in
>> bit_putcs*")
>>
>> diff --git a/drivers/video/fbdev/core/bitblit.c
>> b/drivers/video/fbdev/core/bitblit.c
>> index 085ffb44c51a..6b2f9748cd78 100644
>> --- a/drivers/video/fbdev/core/bitblit.c
>> +++ b/drivers/video/fbdev/core/bitblit.c
>> @@ -87,7 +87,7 @@ static inline void bit_putcs_aligned(struct
>> vc_data *vc, struct fb_info *info,
>> u16 ch = scr_readw(s++) & charmask;
>>
>> if (ch >= charcnt)
>> - ch = 0;
>> + ch = (charcnt - 1);
>> src = vc->vc_font.data + (unsigned int)ch *
>> cellsize;
>>
>> if (attr) {
>> @@ -126,7 +126,7 @@ static inline void bit_putcs_unaligned(struct
>> vc_data *vc,
>> u16 ch = scr_readw(s++) & charmask;
>>
>> if (ch >= charcnt)
>> - ch = 0;
>> + ch = (charcnt - 1);
>> src = vc->vc_font.data + (unsigned int)ch *
>> cellsize;
>>
>> if (attr) {
>>
>
--
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Re: Weird characters in virtual terminal consoles from (CTRL-ALT) F2 to F6 and over F7 William Burrow <wbkernel@gmail.com> - 2025-12-22 03:20 +0100
Re: Weird characters in virtual terminal consoles from (CTRL-ALT) F2 to F6 and over F7 Helge Deller <deller@kernel.org> - 2025-12-22 11:10 +0100
Re: Weird characters in virtual terminal consoles from (CTRL-ALT) F2 to F6 and over F7 Gianluca Renzi <icjtqr@gmail.com> - 2025-12-22 11:10 +0100
Re: Weird characters in virtual terminal consoles from (CTRL-ALT) F2 to F6 and over F7 Gianluca Renzi <gianlucarenzi@eurek.it> - 2025-12-22 12:20 +0100
Re: Weird characters in virtual terminal consoles from (CTRL-ALT) F2 to F6 and over F7 Camaleón <noelamac@gmail.com> - 2025-12-22 16:30 +0100
Re: Weird characters in virtual terminal consoles from (CTRL-ALT) F2 to F6 and over F7 William Burrow <wbkernel@gmail.com> - 2025-12-23 19:00 +0100
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