linux-kernel - Re: [PATCH v4] powerpc: Use shared font data

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Message-ID: <6c805c35-a23d-569e-42ef-f3d875997048@linux-m68k.org>
Date: Thu, 6 Nov 2025 10:48:25 +1100 (AEDT)
From: Finn Thain <fthain@...ux-m68k.org>
To: "Dr. David Alan Gilbert" <linux@...blig.org>
cc: Christophe Leroy <christophe.leroy@...roup.eu>, 
    Stan Johnson <userm57@...oo.com>, mpe@...erman.id.au, npiggin@...il.com, 
    sam@...nborg.org, benh@...nel.crashing.org, linuxppc-dev@...ts.ozlabs.org, 
    linux-kernel@...r.kernel.org, rdunlap@...radead.org, 
    Cedar Maxwell <cedarmaxwell@....com>
Subject: Re: [PATCH v4] powerpc: Use shared font data


On Wed, 5 Nov 2025, Christophe Leroy wrote:

> > I wonder if bodging those in lib/fonts/Makefile for 
> > lib/fonts/font_sun8x16.c fixes it?
> > But... this is data - there's no code is there - are any of those 
> > flags relevant for data only?
> 
> I think -fPIC is relevant for data-only here because font_sun_8x16 
> contains a pointer to fontdata_sun8x16 in font_sun_8x16.data
> 
> I see two things to try:
> 
> 1/ Either build font_sun8x16.o with -fPIC
> 
> diff --git a/lib/fonts/Makefile b/lib/fonts/Makefile
> index e16f68492174a..844306d7b15e9 100644
> --- a/lib/fonts/Makefile
> +++ b/lib/fonts/Makefile
> @@ -20,3 +20,5 @@ font-objs-$(CONFIG_FONT_6x8)       += font_6x8.o
>  font-objs += $(font-objs-y)
> 
>  obj-$(CONFIG_FONT_SUPPORT)         += font.o
> +
> +CFLAGS_font_sun8x16.o             += -fPIC
> 
> 2/ Or add a PTRRELOC:
> 
> diff --git a/arch/powerpc/kernel/btext.c b/arch/powerpc/kernel/btext.c
> index 7f63f1cdc6c39..fc461cfaf4a34 100644
> --- a/arch/powerpc/kernel/btext.c
> +++ b/arch/powerpc/kernel/btext.c
> @@ -20,6 +20,7 @@
>  #include <asm/io.h>
>  #include <asm/processor.h>
>  #include <asm/udbg.h>
> +#include <asm/setup.h>
> 
>  #define NO_SCROLL
> 
> @@ -463,7 +464,7 @@ static noinline void draw_byte(unsigned char c, long locX,
> long locY)
>  {
>  	unsigned char *base	= calc_base(locX << 3, locY << 4);
>  	unsigned int font_index = c * 16;
> -	const unsigned char *font	= font_sun_8x16.data + font_index;
> +	const unsigned char *font	= PTRRELOC(font_sun_8x16.data) +
> font_index;
>  	int rb			= dispDeviceRowBytes;
> 
>  	rmci_maybe_on();
> 

Patch 2 has the virtue that it only needs to be tested on powerpc.
Patch 1 has the virtue that other architectures might benefit.

Commit 0ebc7feae79a ("powerpc: Use shared font data"), which caused the 
regression, has a sparc equivalent in commit 0f1991949d9b ("sparc: Use 
shared font data"). So I wonder whether CONFIG_EARLYFB has also regressed 
(for CONFIG_SPARC64). Maybe QEMU could help answer that question.