[PW_SID:1163390] powerpc: Add ARCH_WARN_ASM and KUnit tests for Rust WARN() support - #2650
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…support
The Rust kernel infrastructure generates inline asm for WARN() via
ARCH_WARN_ASM(file, line, flags, size), expanding it through a C
preprocessor pass (generated_arch_warn_asm.rs.S) to produce an
arch-specific asm template string for use in Rust's core::arch macros.
powerpc currently lacks ARCH_WARN_ASM and ARCH_WARN_REACHABLE, causing
Rust builds to fail on powerpc with
```
error: no rules expected `ARCH_WARN_ASM`
--> /home/linkmauve/dev/linux/wii/rust/kernel/generated_arch_warn_asm.rs:1:28
|
1 | ::kernel::concat_literals!(ARCH_WARN_ASM("{file}", "{line}", "{flags}", "{size}"))
| ^^^^^^^^^^^^^ no rules expected this token in macro call
|
::: ../rust/kernel/lib.rs:279:1
|
279 | macro_rules! concat_literals {
| ---------------------------- when calling this macro
|
= note: while trying to match sequence start
error: no rules expected `ARCH_WARN_REACHABLE`
--> /home/linkmauve/dev/linux/wii/rust/kernel/generated_arch_reachable_asm.rs:1:28
|
1 | ::kernel::concat_literals!(ARCH_WARN_REACHABLE)
| ^^^^^^^^^^^^^^^^^^^ no rules expected this token in macro call
|
::: ../rust/kernel/lib.rs:279:1
|
279 | macro_rules! concat_literals {
| ---------------------------- when calling this macro
|
= note: while trying to match sequence start
error: aborting due to 2 previous errors
```
To add ARCH_WARN_ASM, _EMIT_BUG_ENTRY first needs to be refactored.
The old definition was a bare macro with no parameters, relying on
positional asm operand references (%0-%3), hardcoding the backward
reference to local label 1b, and including .org/.previous directives
inline. That made it impossible to compose as a plain string outside of
an asm operand context, and left an invisible contract that callers must
always emit their trap at label 1:.
Refactor _EMIT_BUG_ENTRY to take explicit (label, file, line, flags)
string arguments via string concatenation. This removes the dependency
on asm operand numbering and makes the trap label an explicit argument,
so the caller's intent is visible at the call site and a future caller
using a different label cannot silently produce a wrong bug table entry.
Move the .org and .previous directives out of _EMIT_BUG_ENTRY and into
each call site, so BUG_ENTRY() can still pass sizeof(struct bug_entry)
as an asm operand while ARCH_WARN_ASM can supply its own size string
independently.
Add ARCH_WARN_REACHABLE as an empty define, matching the arm64
convention, indicating that no additional reachability annotation is
needed after a WARN on powerpc.
This brings powerpc into line with x86, arm64, s390, and riscv, all of
which already define ARCH_WARN_ASM and ARCH_WARN_REACHABLE.
Reported-by: FUJITA Tomonori <tomo@flapping.org>
Closes: https://lore.kernel.org/all/anG67Q6Y59kDqh-c@desktop
Fixes: 73b741a ("rust: Add PowerPC support")
Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>
Signed-off-by: Linux RISC-V bot <linux.riscv.bot@gmail.com>
…ssion
Verify that the __bug_table entry emitted by ARCH_WARN_ASM has a correct
bug_addr displacement — i.e. the '1b' label reference in _EMIT_BUG_ENTRY
resolves to the trap instruction — by calling find_bug() with the exact
virtual address of the twi instruction, mirroring what the real powerpc
trap handler does.
The trap address is captured at link time via a .dc.a 1b relocation placed
in .data by the global_asm! block. global_asm! is used instead of asm!
because LLVM eliminates asm! blocks in dead branches; global_asm! is
file-scope and always emitted. BUG_KUNIT_TRAP_ADDR is defined as a .global
symbol directly on the .dc.a word so the linker relocation lands on it —
a Rust static initialized to zero would end up in BSS where relocations are
not applied.
.dc.a emits a pointer-width word (4 bytes on ppc32, 8 bytes on ppc64),
so BUG_KUNIT_TRAP_ADDR is declared as usize on the Rust side, making the
tests correct on both ppc32 and ppc64. The global_asm! block is split into
two cfg-gated variants (CONFIG_PPC64 / !CONFIG_PPC64) to select the right
.balign since concat!() only accepts literals.
Five tests are included in the rust_kernel_bug_powerpc suite:
bug_entry_found - find_bug() returns non-NULL for the trap address,
proving the bug_addr displacement is correct
bug_entry_is_warning - the emitted entry has BUGFLAG_WARNING set
bug_entry_file - bug_get_file_line() returns the correct source
file (requires CONFIG_DEBUG_BUGVERBOSE)
bug_entry_line - the recorded line number is non-zero, confirming
the {line} operand was substituted correctly
(requires CONFIG_DEBUG_BUGVERBOSE)
bug_entry_addr_is_in_text - kernel_text_address() confirms the trap address
lies in kernel text, not data or zero
The suite is named rust_kernel_bug_powerpc and the Kconfig option
CONFIG_RUST_BUG_POWERPC_KUNIT_TEST depends on PPC && GENERIC_BUG,
covering both ppc32 and ppc64.
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.
Assisted-by: LLM
Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>
Signed-off-by: Linux RISC-V bot <linux.riscv.bot@gmail.com>
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PR for series 1163390 applied to workflow__riscv__fixes
Name: powerpc: Add ARCH_WARN_ASM and KUnit tests for Rust WARN() support
URL: https://patchwork.kernel.org/series/1163390/
Version: 4