[PATCH] fbdev/arm: Export acorndata_8x8 font symbol for bootloader

[PATCH] fbdev/arm: Export acorndata_8x8 font symbol for bootloader

[Helge Deller]

The text display code used in the Risc PC kernel image decompression
code uses arch/arm/boot/compressed/font.c, which includes
lib/fonts/font_acorn_8x8.c, which further includes <linux/font.h>.

Since commit 97df8960240a ("lib/fonts: Provide helpers for calculating
glyph pitch and size") <linux/font.h> contains inline functions that
require __do_div64, which is not linked into the ARM kernel
decompressor. This makes Risc PC zImages fail to build.

Resolve this issue by defining the BOOTLOADER symbol and use it to avoid
a static declaration of the acorndata_8x8 symbol. That way it can be
referenced by the arm bootloader, and other static math functions and
symbols (like __do_div64) stay static and don't get unneccesary included
in the ARM kernel bootloader decompressor object file.

Fixes: 97df8960240a ("lib/fonts: Provide helpers for calculating glyph pitch and size")
Reported-by: Ethan Nelson-Moore <enelsonmoore@gmail.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Russell King <linux@armlinux.org.uk>
Signed-off-by: Helge Deller <deller@gmx.de>
---
 arch/arm/boot/compressed/Makefile | 2 +-
 lib/fonts/font_acorn_8x8.c        | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
index a159120d1e42..e3f550d62857 100644
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -157,4 +157,4 @@ $(obj)/piggy_data: $(obj)/../Image FORCE
 
 $(obj)/piggy.o: $(obj)/piggy_data
 
-CFLAGS_font.o := -Dstatic=
+CFLAGS_font.o := -DBOOTLOADER
diff --git a/lib/fonts/font_acorn_8x8.c b/lib/fonts/font_acorn_8x8.c
index 36c51016769d..4ff52c79f8c4 100644
--- a/lib/fonts/font_acorn_8x8.c
+++ b/lib/fonts/font_acorn_8x8.c
@@ -5,7 +5,12 @@
 
 #define FONTDATAMAX 2048
 
+#ifdef BOOTLOADER
+/* The acorndata_8x8 symbol is needed by the ARM bootloader too. */
+const struct font_data acorndata_8x8 = {
+#else
 static const struct font_data acorndata_8x8 = {
+#endif
 { 0, 0, FONTDATAMAX, 0 }, {
 /* 00 */  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, /* ^@ */
 /* 01 */  0x7e, 0x81, 0xa5, 0x81, 0xbd, 0x99, 0x81, 0x7e, /* ^A */
-- 
2.54.0

Re: [PATCH] fbdev/arm: Export acorndata_8x8 font symbol for bootloader

[Russell King (Oracle)]

On Tue, Jun 09, 2026 at 11:10:56AM +0200, Helge Deller wrote:
> The text display code used in the Risc PC kernel image decompression
> code uses arch/arm/boot/compressed/font.c, which includes
> lib/fonts/font_acorn_8x8.c, which further includes <linux/font.h>.
> 
> Since commit 97df8960240a ("lib/fonts: Provide helpers for calculating
> glyph pitch and size") <linux/font.h> contains inline functions that
> require __do_div64, which is not linked into the ARM kernel
> decompressor. This makes Risc PC zImages fail to build.
> 
> Resolve this issue by defining the BOOTLOADER symbol and use it to avoid
> a static declaration of the acorndata_8x8 symbol. That way it can be
> referenced by the arm bootloader, and other static math functions and
> symbols (like __do_div64) stay static and don't get unneccesary included
> in the ARM kernel bootloader decompressor object file.

The decompressor font support has actually been broken since:

commit 6735b4632def0640dbdf4eb9f99816aca18c4f16
Author: Peilin Ye <yepeilin.cs@gmail.com>
Date:   Thu Sep 24 09:42:22 2020 -0400

    Fonts: Support FONT_EXTRA_WORDS macros for built-in fonts

which added extra data to the beginning of the array of font
information:

ENTRY(ll_write_char)
        stmfd   sp!, {r4 - r7, lr}
...
        /*
         * calculate offset into character table
         */
        mov     r1, r1, lsl #3

r1 is the character, this multiplies the character value by 8.

        adr     ip, LC0
        ldmia   ip, {r3, r4, r5, r6, lr}
        sub     ip, ip, r3
        add     r6, r6, ip

in conjunction with the data table:

LC0:    .word   LC0
        .word   bytes_per_char_h
        .word   video_size_row
        .word   acorndata_8x8
        .word   con_charconvtable

results in r6 pointing at acorndata_8x8. We then index this using the
modified character value above:

        orr     r1, r1, #7
        ldrb    r7, [r6, r1]

This breaks if extra data is added to the start, and thus has been
broken since the above commit.

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