Re: [BUG] silent hangup when debugging lib/fdtdec.c

[alexander.feilke@ew.tq-group.com]

On Tuesday, November 25, 2025 17:35 CET, Tom Rini <trini at konsulko.com> wrote:

> On Tue, Nov 25, 2025 at 05:14:12PM +0100, Alexander Feilke wrote:
> 
> > From: Alexander Feilke <alexander.feilke at ew.tq-group.com>
> > 
> > Description: U-Boot hangs silently during boot when enabling DEBUG in
> > lib/fdtdec.c
> > 
> > Not sure if its really a bug or rather a configuration issue on my side.
> > 
> > Minimal steps to reproduce: <see patch>
> > 
> > The hang is caused by `panic("FDT overlap");` later inside the if block.
> > (see `lib/fdtdec.c:1279` in `fdt_find_separate(void)`)
> > 
> > Additionally, no boot log can be seen because serial is initialized after
> > loading the devicetree in this boot stage (see `common/board_r.c:665` in
> > `initcall_run_r(void)`)
> > 
> > Tested on i.MX6 with configs for tqma6d_mba6 and other tq boards that aren't,
> > mainlined yet (tqma6ulx_mba6ul and tqma7d_mba7).
> > 
> > Any idea what to look for to fix this on our side?
> > 
> > Thanks in advance,
> > Alexander
> 
> For very early failures you might need to look at enabling DEBUG_UART
> which wires in a more direct "just write this to serial port".
> 
> -- 
> Tom

Thanks for pointing that out. The debug log shows that the global data is
still located in the SRAM after relocation.
Printing all variables involved in the panic condition shows, that the stack
pointer also overflowed, so there appear to be two separate issues.

if (top > (void *)gd || top > (void *)&stack_ptr) {

including top, sp and sys_init_sp_addr for completeness:

<debug_uart>
FDT 8789d3a0 gd 0091de40
top 878a7aa8 sp 878543e7
sys_init_sp_addr 0091ff20
FDT overlap
resetting ...
System reset not supported on this platform
### ERROR ### Please RESET the board ###


Note: I don't use CUSTOM_SYS_INIT_SP_ADDR so the default is used. GENERATED_GBL_DATA_SIZE is 0xe0

#define SYS_INIT_SP_ADDR	(CFG_SYS_INIT_RAM_ADDR + CFG_SYS_INIT_RAM_SIZE
 - GENERATED_GBL_DATA_SIZE)
#define CFG_SYS_INIT_RAM_ADDR	IRAM_BASE_ADDR
#define CFG_SYS_INIT_RAM_SIZE	IRAM_SIZE

Do you have any idea how to address these two problems?

Alexander