[PATCH v2 0/7] arm64: stack backtraces

[Peng Fan]

On Fri, Jul 25, 2025 at 02:57:04PM +0200, Casey Connolly wrote:
>Implement support for printing stack backtraces on ARM64, make
>framepointer support configurable by the build system with
>CONFIG_FRAMEPOINTER and teach U-Boot to walk the framepointers and
>unwind the stack when an exception occurs. Also show all 64 bits of the
>exception syndrom register (ESR).
>
>Additionally, a new global unwind_stack() function is added, this can
>be called from anywhere to print a backtrace which can be useful when
>debugging certain problems.
>
>In the future, stack unwinding with symbol support could be extended
>to for example only emit log messages when a function is called in a
>specific code path. This would allow for less noise when debugging hot
>paths under certain conditions, but this feature is left as future work.
>
>=== Handling relocation ===
>
>Since U-Boot relocates itself at runtime, and can be built to be
>position independent in the first place (effectively "relocating" itself
>when it first starts too), we can't really rely on gd->reloc_off.
>
>The approach taken here is to subtract CONFIG_TEXT_BASE from the address
>of each symbol in the lookup table (while it's being generated), then
>when decoding we just subtract the address of the _start label since it
>is always correct pre and post relocation. This allows us to avoid all
>the awkward maths since the symbols are always relative to 0x0 in the
>lookup table.
>
>Example output:
>
>"Synchronous Abort" handler, esr 0x0000000096000004, far 0xfffffffffffff
>elr: 000000009fc6f768 lr : 000000009fc6f710 (reloc)
>elr: 00000001ffe49768 lr : 00000001ffe49710
>x0 : 000fffffffffffff x1 : 0000000000000009
>x2 : 00000001efdbadd0 x3 : 0000000000000000
>x4 : 00000001efd99a28 x5 : 00000001ffec7676
>x6 : 00000001efdbac70 x7 : 0000000000000000
>x8 : 0000000000000002 x9 : 0000000000000034
>x10: 000000000000000d x11: 0000000000000006
>x12: 0000000000001000 x13: 00000000c3400000
>x14: 00000000fffffff8 x15: 00000001efd99837
>x16: 00000001ffe146b8 x17: 0000000000000000
>x18: 00000001efdbac70 x19: 000000000a6f8800
>x20: 00000001efe06fd0 x21: 0000000000000001
>x22: 00000001ffef5b80 x23: 00000001ffee08c0
>x24: 0000000000000002 x25: 0000000000000000
>x26: 0000000000000000 x27: 0000000000000000
>x28: 00000001efe512c0 x29: 00000001efd99c80
>
>Code: 2a010000 b9001260 d5033fbf 92fffe00 (39400001)
>
>CONFIG_TEXT_BASE   : 0x9fc00000
>Relocated base addr: 0x1ffdda000
>Backtrace:
>	<0x000001ffe496d0> dwc3_qcom_glue_configure+0x40
>	<0x000001ffe494a4> dwc3_glue_probe+0x10c
>	<0x000001ffe1757c> device_probe+0x254
>	<0x000001ffe1757c> device_probe+0x114
>	<0x000001ffe4ff70> usb_init+0x158
>	<0x000001ffe00fe4> do_usb_start+0xc
>	<0x000001ffe01018> do_usb+0x78
>	<0x000001ffe0dec4> cmd_process+0x140
>	<0x000001ffe04e24> run_list_real+0x6f0
>	<0x000001ffe05554> parse_stream_outer+0x148
>	<0x000001ffe04d30> parse_string_outer+0x90
>	<0x000001ffe0d148> run_command_list+0x50
>	<0x000001ffe02be0> main_loop+0x28
>	<0x000001ffe065c0> board_init_r+0x3c8
>	<0x000001ffddd00c> relocation_return+0x4

Nit: If this address could be printed with pre-relocated address
(built address in elf), it would be better.

Regards
Peng

>
>Resetting CPU ...
>
>---
>Changes in v2:
>- Include calling function in backtrace (current LR)
>- Implement support for runtime symbol lookup
>- Use symbol lookup to print more informative backtraces when available
>- Adjust backtrace format and print U-Boot base address
>- Link to v1: https://lore.kernel.org/u-boot/20250703051951.43372-1-heinrich.schuchardt@canonical.com
>
>To: Tom Rini <trini at konsulko.com>
>To: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
>Cc: Simon Glass <sjg at chromium.org>
>Cc: Marek Vasut <marek.vasut+renesas at mailbox.org>
>Cc: Ben Dooks <ben.dooks at codethink.co.uk>
>Cc: Rick Chen <rick at andestech.com>
>Cc: Leo <ycliang at andestech.com>
>Cc: Ilias Apalodimas <ilias.apalodimas at linaro.org>
>Cc: u-boot at lists.denx.de
>
>---
>Casey Connolly (3):
>      drop unused kallsyms support
>      add support for symbol lookups
>      arm64: implement printing backtraces with symbols
>
>Heinrich Schuchardt (4):
>      cmd/exception: missing include string.h
>      Kconfig: make CONFIG_FRAMEPOINTER available on arm64
>      arm64: initialize the frame pointer register
>      arm64: simplify interrupt code
>
> Kconfig                      |  25 ++
> Makefile                     |  24 +-
> arch/arm/Makefile            |   9 +-
> arch/arm/lib/crt0_64.S       |   1 +
> arch/arm/lib/interrupts_64.c | 133 ++++++---
> arch/riscv/Kconfig           |  21 --
> common/Makefile              |   1 -
> common/kallsyms.c            |  42 ---
> common/system_map.c          |   8 -
> include/exception.h          |   1 +
> include/symbols.h            |  22 ++
> lib/Kconfig                  |   9 +
> lib/symbols.c                | 141 ++++++++++
> tools/Makefile               |   3 +
> tools/symbols.c              | 646 +++++++++++++++++++++++++++++++++++++++++++
> 15 files changed, 965 insertions(+), 121 deletions(-)
>---
>base-commit: f2f451d9d6d3756458d5037e3e5135e5211582d7
>
>// Caleb (they/them)
>