[PATCH master 0/3] Fix GCC 11 THUMB2 relocate_to_current_adr miscompile

Ahmad Fatoum a.fatoum at pengutronix.de
Thu Oct 13 02:03:49 PDT 2022

TL;DR: GCC can prove that variables aren't supposed to overlap and as
such it generated code than readded get_runtime_offset() on top of an
already relocated linker-defined variable's address.
See PATCH 2/3 for a disassembly of the affected code. Board code can
be similarly micompiled, but that's a fix for another day.

I am not so sure about the name of the new macro. I chose
get_unrelocated for similarity with get_unaligned, but it doesn't
dereference the argument, just get its address. Looking at it that way,
it's just a UB-infested way to say & (address-of). Perhaps just
call it runtime_address()? After all, it works before and after
relocation. We can change that later though, once I get around
to patch board entry points.

Ahmad Fatoum (3):
  include: asm-generic: reloc: implement get_unrelocated()
  ARM: cpu: add compiler barrier around unrelocated access
  RISC-V: add compiler barriers around unrelocated accesses

 arch/arm/cpu/common.c             | 11 +++--
 arch/arm/cpu/uncompress.c         |  4 +-
 arch/riscv/boot/uncompress.c      |  4 +-
 arch/riscv/include/asm/sections.h |  2 +-
 arch/riscv/lib/reloc.c            |  6 +--
 include/asm-generic/reloc.h       | 68 +++++++++++++++++++++++++++++++
 6 files changed, 81 insertions(+), 14 deletions(-)


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