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 change to the font bitmap pointer that's used when btext_init() begins painting characters on the display, early in the boot process.
Christophe Leroy explains, "before kernel text is relocated to its final location ... data is addressed with an offset which is added to the Global Offset Table (GOT) entries at the start of bootx_init() by function reloc_got2(). But the pointers that are located inside a structure are not referenced in the GOT and are therefore not updated by reloc_got2(). It is therefore needed to apply the offset manually by using PTRRELOC() macro."
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@ya... 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") Suggested-by: Christophe Leroy christophe.leroy@csgroup.eu Signed-off-by: Finn Thain fthain@linux-m68k.org --- Changed since v1: - Improved commit log entry to better explain the need for PTRRELOC(). --- 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();