[PATCH] powerpc: Use relocated font data pointer for btext_drawchar()

[Finn Thain <fthain@linux-m68k.org>]

From: Christophe Leroy <christophe.leroy@csgroup.eu>

Since Linux v6.7, booting using BootX on an Old World PowerMac produces
an early crash. Stan Johnson writes, "the symptoms are that the screen
goes blank and the backlight stays on, and the system freezes (Linux
doesn't boot)."
Further testing revealed that the failure can be avoided by disabling
CONFIG_BOOTX_TEXT. Bisection revealed that the regression was caused by
a patch which replaced the static btext font data with const data in a
different compilation unit. To fix this, access the font data at its
relocated address.

Cc: Cedar Maxwell <cedarmaxwell@mac.com>
Cc: Stan Johnson <userm57@yahoo.com>
Cc: "Dr. David Alan Gilbert" <linux@treblig.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: stable@vger.kernel.org
Link: https://lists.debian.org/debian-powerpc/2025/10/msg00111.html
Link: https://lore.kernel.org/linuxppc-dev/d81ddca8-c5ee-d583-d579-02b19ed95301@yahoo.com/
Reported-by: Cedar Maxwell <cedarmaxwell@mac.com>
Closes: https://lists.debian.org/debian-powerpc/2025/09/msg00031.html
Bisected-by: Stan Johnson <userm57@yahoo.com>
Tested-by: Stan Johnson <userm57@yahoo.com>
Fixes: 0ebc7feae79a ("powerpc: Use shared font data")
Signed-off-by: Finn Thain <fthain@linux-m68k.org>

---

Christophe, as you're the author of this patch, this submission will
probably need your sign-off.

---
 arch/powerpc/kernel/btext.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/btext.c b/arch/powerpc/kernel/btext.c
index 7f63f1cdc6c3..ca00c4824e31 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();
-- 
2.49.1