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[v2,0/3] ARM64: add symbol name lookup and print a backtrace on exception

Message ID 20240808-arm64-backtrace-v2-0-29665a2265cf@linaro.org
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Series ARM64: add symbol name lookup and print a backtrace on exception | expand

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Caleb Connolly Aug. 8, 2024, 4:21 p.m. UTC 
U-Boot already emits frame pointers on ARM64, but lacks the code to
parse them, as well as a mechanism for looking up symbol names at
runtime.

There was some (seemingly?) leftover code for symbols lookups in
common/kallsyms.c and associated parts in the makefile, however it
appears to be entirely unused and unsupported. It relied on generating
one long string of all symbol addresses and names.

The approach taken here is instead largely based on the implementation
in the Xen hypervisor, it performs basic compression using non-ASCII
bytes to tokenize repeated string segments which can later be expanded
back out at runtime.

This is then utilized in the ARM64 interrupt handling routine to dump a
backtrace in the show_regs() debug function. As well as providing a
general purpose unwind_stack() function which can be used for debugging.

== 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
this label address is updated to make U-Boot position independent and
during relocation, it allows us to avoid re-implementing the relocation
state handling stuff in the symbol decoder.

== Size ==

By default this feature is off, and will not effect the size of U-Boot
binaries. The generated symbols object file is ~85k with the (fairly
hefty) qcom_defconfig, so there is certainly a cost to be taken into
account.

I hope that this implementation can be later extended for other
platforms. However this is currently beyond my (skill, time)
capabilities.

---
Changes in v2:
- Remove unused last_fp pointer
- Apply Tom's suggestions (cleanup hunks, don't guard unwind_stack()).
- Link to v1: https://lore.kernel.org/r/20240710-arm64-backtrace-v1-0-5a2ba50485dd@linaro.org

---
Caleb Connolly (3):
      drop unused kallsyms support
      add support for symbol lookups
      arm64: unwind stack on exception

 Makefile                      |  24 +-
 arch/arm/include/asm/ptrace.h |   2 +
 arch/arm/lib/interrupts_64.c  |  75 +++++
 common/Makefile               |   1 -
 common/kallsyms.c             |  43 ---
 common/system_map.c           |   8 -
 include/symbols.h             |  19 ++
 lib/Kconfig                   |   8 +
 lib/symbols.c                 | 126 ++++++++
 tools/Makefile                |   3 +
 tools/symbols.c               | 646 ++++++++++++++++++++++++++++++++++++++++++
 11 files changed, 892 insertions(+), 63 deletions(-)
---
change-id: 20240710-arm64-backtrace-2926f764dbdc
base-commit: 13f9c5668411aa18ef64846d5bc86e9e6be52082

// Caleb (they/them)