Console text selection bug

Console text selection bug

[Giuliano Pochini]

When I select text in console it's scrambled. I looked at the
aty128 sources, but I didn't find anything about it. Where is
the code that manages selection/cut/paste ?

The selected text is scrambled in this way: every char has
the bits 1,2,3 swapped with bits 5,6,7 respectively (bits
numbered left to right). I don't know what can cause this
strange behaviour... I thought the console screen was a
simple array of char/colour pairs.

[b/w G3, r128, all kernels]

Bye.


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Re: Console text selection bug

[Benjamin Herrenschmidt]

>When I select text in console it's scrambled. I looked at the
>aty128 sources, but I didn't find anything about it. Where is
>the code that manages selection/cut/paste ?
>
>The selected text is scrambled in this way: every char has
>the bits 1,2,3 swapped with bits 5,6,7 respectively (bits
>numbered left to right). I don't know what can cause this
>strange behaviour... I thought the console screen was a
>simple array of char/colour pairs.

It's an endian bug in fbcon when accessing the text/attribute buffer.

I think someone posted a fix for it, You may have more luck asking on
the fbdev mailing list to the fbdev maintainers what's up.

I think it's related to fbcon_invert_region() not using the access
macros and directly tapping the buffer, causing attributes & text
to be messed up.

Ben.

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Re: Console text selection bug

[Timothy A. Seufert]

At 10:35 PM +0100 3/5/01, Benjamin Herrenschmidt wrote:
>>When I select text in console it's scrambled. I looked at the
>>aty128 sources, but I didn't find anything about it. Where is
>>the code that manages selection/cut/paste ?
>>
>>The selected text is scrambled in this way: every char has
>>the bits 1,2,3 swapped with bits 5,6,7 respectively (bits
>>numbered left to right). I don't know what can cause this
>>strange behaviour... I thought the console screen was a
>>simple array of char/colour pairs.
>
>It's an endian bug in fbcon when accessing the text/attribute buffer.
>
>I think someone posted a fix for it, You may have more luck asking on
>the fbdev mailing list to the fbdev maintainers what's up.
>
>I think it's related to fbcon_invert_region() not using the access
>macros and directly tapping the buffer, causing attributes & text
>to be messed up.

I saw this problem in 2.4.x until I turned off the config option for
VGA consoles.  Then it went away.

   Tim Seufert

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Re: Console text selection bug

[Geert Uytterhoeven]

On Mon, 5 Mar 2001, Timothy A. Seufert wrote:
> At 10:35 PM +0100 3/5/01, Benjamin Herrenschmidt wrote:
> >>When I select text in console it's scrambled. I looked at the
> >>aty128 sources, but I didn't find anything about it. Where is
> >>the code that manages selection/cut/paste ?
> >>
> >>The selected text is scrambled in this way: every char has
> >>the bits 1,2,3 swapped with bits 5,6,7 respectively (bits
> >>numbered left to right). I don't know what can cause this
> >>strange behaviour... I thought the console screen was a
> >>simple array of char/colour pairs.
> >
> >It's an endian bug in fbcon when accessing the text/attribute buffer.
> >
> >I think someone posted a fix for it, You may have more luck asking on
> >the fbdev mailing list to the fbdev maintainers what's up.
> >
> >I think it's related to fbcon_invert_region() not using the access
> >macros and directly tapping the buffer, causing attributes & text
> >to be messed up.
>
> I saw this problem in 2.4.x until I turned off the config option for
> VGA consoles.  Then it went away.

Nevertheless, it's a bug. Can someone please change fbcon_invert_region() to
use scr_{read,write}w() to access the shadow screen buffer and see whether it
works? Patches are accepted at linux-fbdev-devel@lists.sourceforge.net :-)

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds


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Re: Console text selection bug

[Giuliano Pochini]

>> It's an endian bug in fbcon when accessing the text/attribute buffer.

> Nevertheless, it's a bug. Can someone please change fbcon_invert_region() to
> use scr_{read,write}w() to access the shadow screen buffer and see whether it
> works? Patches are accepted at linux-fbdev-devel@lists.sourceforge.net :-)

Yes, it's an endianess bug.  scr_{read,write}w() are defined as normal
assignments in vt_buffer.h, so I wonder where is the bug. Is the shadow buffer
supposed to be native endian ?


Bye.


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Re: Console text selection bug

[Geert Uytterhoeven]

On Wed, 7 Mar 2001, Giuliano Pochini wrote:
> >> It's an endian bug in fbcon when accessing the text/attribute buffer.
>
> > Nevertheless, it's a bug. Can someone please change fbcon_invert_region() to
> > use scr_{read,write}w() to access the shadow screen buffer and see whether it
> > works? Patches are accepted at linux-fbdev-devel@lists.sourceforge.net :-)
>
> Yes, it's an endianess bug.  scr_{read,write}w() are defined as normal
> assignments in vt_buffer.h, so I wonder where is the bug. Is the shadow buffer

No, their definition in vt_buffer.h depends on VT_BUF_HAVE_RW. If that is
defined in <asm/vga.h>, vga.h must provide its own definitions.

> supposed to be native endian ?

It doesn't really matter, since all accesses must be done using
scr_{read,write}w() anyway. For performance reasons we chose native endianness.
Except when VGA (CONFIG_VGA_CONSOLE || CONFIG_MDA_CONSOLE) is defined, since on
VGA/MDA the shadow buffer _is_ the screen image and must be little endian.

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds


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Re: Console text selection bug

[Hollis R Blanchard]

On Sat, 3 Mar 2001, Giuliano Pochini wrote:
>
> When I select text in console it's scrambled. I looked at the
> aty128 sources, but I didn't find anything about it. Where is
> the code that manages selection/cut/paste ?
>
> The selected text is scrambled in this way: every char has
> the bits 1,2,3 swapped with bits 5,6,7 respectively (bits
> numbered left to right). I don't know what can cause this
> strange behaviour... I thought the console screen was a
> simple array of char/colour pairs.
>
> [b/w G3, r128, all kernels]

I don't see this (B&W G3, 2.2.19pre14). I understand this is only a problem if
you enable VGA console (which I don't have enabled).

-Hollis


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