[PATCH v4 0/2] powerpc: Add ARCH_WARN_ASM and KUnit tests for Rust WARN() support

[Mukesh Kumar Chaurasiya (IBM)]

powerpc currently has no ARCH_WARN_ASM or ARCH_WARN_REACHABLE definitions,
which causes Rust kernel builds on powerpc to fail with a macro expansion
error when the generic Rust WARN() infrastructure tries to call
ARCH_WARN_ASM() through generated_arch_warn_asm.rs.S. Every other
architecture that supports Rust (x86, arm64, s390, riscv) already provides
these definitions. This series brings powerpc into line.

Patch 1 refactors _EMIT_BUG_ENTRY in arch/powerpc/include/asm/bug.h.
The old macro was a positional-operand template that hardcoded the 1b
label reference and embedded .org/.previous directives, making it
impossible to compose as a free string outside an asm operand context.
The refactored version takes explicit (label, file, line, flags) arguments
via string concatenation; .org/.previous are moved to each call site so
BUG_ENTRY() can continue to pass sizeof(struct bug_entry) as an asm
operand while ARCH_WARN_ASM supplies its own size string. With
_EMIT_BUG_ENTRY composable as a plain string, adding ARCH_WARN_ASM and
ARCH_WARN_REACHABLE is then straightforward.

Patch 2 adds five KUnit tests under CONFIG_RUST_BUG_POWERPC_KUNIT_TEST
(depends on PPC && GENERIC_BUG, covering both ppc32 and ppc64) that
verify the __bug_table entry emitted by ARCH_WARN_ASM is correctly
formed. find_bug() is called with the exact virtual address of the twi
instruction, captured at link time via a .dc.a relocation in a
global_asm! block. .dc.a emits a pointer-width word (4 bytes on ppc32,
8 bytes on ppc64); BUG_KUNIT_TRAP_ADDR is declared as usize on the Rust
side so the same test code is correct on both. The five tests check that
the entry is found, carries BUGFLAG_WARNING, records the right source
file and a non-zero line number, and that the trap address lies in
kernel text.

Changelog:
V3 -> V4:
 - Fix Label with appending b at end 
 - Add KUnit test patch.
 - Tested on ppc64le pseries:
   pass:5 fail:0 skip:0.
 - Tested on ppc32 QEMU mac99 G4:
   pass:5 fail:0 skip:0.
 - Tested on ppc64le QEMU pseries:
   pass:5 fail:0 skip:0.
V3: https://lore.kernel.org/all/20260910100801.2159785-2-mkchauras@xxxxxxxxx

V2 -> V3:
 - Add label argument in _EMIT_BUG_ENTRY
V2: https://lore.kernel.org/all/20260910071252.1950488-2-mkchauras@xxxxxxxxx

V1 -> V2:
- commit message now has error, fixes tag and closes tag
V1: https://lore.kernel.org/all/20260819084825.969116-1-mkchauras@xxxxxxxxx



Mukesh Kumar Chaurasiya (IBM) (2):
  powerpc/bug: Add ARCH_WARN_ASM and refactor _EMIT_BUG_ENTRY for Rust
    support
  rust: kernel: Add KUnit tests for powerpc ARCH_WARN_ASM bug table
    emission

 arch/powerpc/include/asm/bug.h |  36 ++++---
 rust/kernel/Kconfig.test       |  13 +++
 rust/kernel/bug.rs             | 171 +++++++++++++++++++++++++++++++++
 3 files changed, 204 insertions(+), 16 deletions(-)

-- 
2.55.0