Verify that the __bug_table entry emitted by ARCH_WARN_ASM has a correct
bug_addr displacement — i.e. the arch's trap label reference resolves to
the trap instruction — by calling find_bug() with the exact virtual address
of the trap, mirroring what the real trap handler does.
To support all architectures, each arch that implements ARCH_WARN_ASM now
defines ARCH_WARN_ASM_TRAP_LABEL, a string constant naming the local label
at which the trap instruction is placed:
x86 "1" (ud2 at label 1:)
powerpc "1" (twi at label 1:)
riscv "1" (ebreak at label 1:)
arm64 "14471" (brk placed at 14471: by __BUG_ENTRY_END)
s390 "0" (mc at label 0:)
The label is used consistently: in ARCH_WARN_ASM itself, in the
bug_addr back-reference inside __BUG_ENTRY / _EMIT_BUG_ENTRY, and in
the new generated_arch_warn_asm_trap_label.rs template, which the
C preprocessor expands at build time into a .rs file included by the
test's 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 in .data on top of a
.dc.a {trap_label}b relocation so the linker resolves the trap address
into it at link time. A Rust static initialized to zero would land in
BSS where relocations are not applied.
The global_asm! string mirrors warn_flags!() exactly — same "/* {size} */"
prefix, same generated_arch_warn_asm.rs and generated_arch_reachable_asm.rs
includes, same operands — plus the .pushsection/.dc.a/.popsection tail.
This keeps the test structurally in sync with the macro it exercises.
The CONFIG_RUST_BUG_WARN_ASM_KUNIT_TEST option depends on GENERIC_BUG
and excludes ARM, LOONGARCH, and UML (which use a different warn_flags!
path without ARCH_WARN_ASM).
Five tests are included in the rust_kernel_bug_warn_asm suite:
bug_entry_found - find_bug() returns non-NULL for the trap
address, proving bug_addr 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 (CONFIG_DEBUG_BUGVERBOSE only)
bug_entry_line - recorded line number is non-zero, confirming
the {line} operand was substituted correctly
(CONFIG_DEBUG_BUGVERBOSE only)
bug_entry_addr_is_in_text - kernel_text_address() confirms the trap
address lies in kernel text
Tested (pass:5 fail:0 skip:0) on:
x86_64 - QEMU x86_64
powerpc - QEMU pseries ppc64le (pseries_le_defconfig)
riscv - QEMU riscv64
arm64 - QEMU aarch64
s390 - QEMU s390x
Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <[email protected]>
---
Note: I sent this out as a powerpc specific tests earlier. During review
process some people wanted these to be arch independent. Hence sending
this out as an RFC.
Earlier version:
https://lore.kernel.org/all/[email protected]/
arch/arm64/include/asm/asm-bug.h | 3 +
arch/powerpc/include/asm/bug.h | 22 +-
arch/riscv/include/asm/bug.h | 5 +-
arch/s390/include/asm/bug.h | 4 +-
arch/x86/include/asm/bug.h | 5 +-
rust/Makefile | 2 +-
rust/kernel/.gitignore | 1 +
rust/kernel/Kconfig.test | 15 ++
rust/kernel/bug.rs | 191 ++++++++++++++++++
.../generated_arch_warn_asm_trap_label.rs.S | 7 +
10 files changed, 239 insertions(+), 16 deletions(-)
create mode 100644 rust/kernel/generated_arch_warn_asm_trap_label.rs.S
diff --git a/arch/arm64/include/asm/asm-bug.h b/arch/arm64/include/asm/asm-bug.h
index a5f13801b784..e0694543115e 100644
--- a/arch/arm64/include/asm/asm-bug.h
+++ b/arch/arm64/include/asm/asm-bug.h
@@ -60,6 +60,9 @@ _BUGVERBOSE_LOCATION(__FILE__, __LINE__) \
".short " flags ";" \
__stringify(__BUG_ENTRY_END)
+/* Trap instruction is placed at label 14471: by __BUG_ENTRY_END */
+#define ARCH_WARN_ASM_TRAP_LABEL "14471"
+
#define ARCH_WARN_ASM(file, line, flags, size) \
__BUG_ENTRY_STRING(file, line, flags) \
__stringify(brk BUG_BRK_IMM)
diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
index bf31ee1e902a..f0333c564d4f 100644
--- a/arch/powerpc/include/asm/bug.h
+++ b/arch/powerpc/include/asm/bug.h
@@ -32,6 +32,8 @@
#endif /* verbose */
#else /* !__ASSEMBLER__ */
+#define ARCH_WARN_ASM_TRAP_LABEL "1"
+
#ifdef CONFIG_DEBUG_BUGVERBOSE
#define _EMIT_BUG_ENTRY(bug_entry, trap, file, line, flags) \
".section __bug_table,\"aw\"\n" \
@@ -45,21 +47,21 @@
" .short " flags "\n"
#endif
-#define BUG_ENTRY(cond_str, insn, flags, ...) \
- __asm__ __volatile__( \
- "1: " insn "\n" \
- _EMIT_BUG_ENTRY(2, 1b, "%0", "%1", "%2") \
- ".org 2b+%3\n" \
- ".previous\n" \
+#define BUG_ENTRY(cond_str, insn, flags, ...) \
+ __asm__ __volatile__( \
+ ARCH_WARN_ASM_TRAP_LABEL ": " insn "\n" \
+ _EMIT_BUG_ENTRY(2, 1b, "%0", "%1", "%2") \
+ ".org 2b+%3\n" \
+ ".previous\n" \
: : "i" (WARN_CONDITION_STR(cond_str) __FILE__), "i"
(__LINE__), \
"i" (flags), \
"i" (sizeof(struct bug_entry)), \
##__VA_ARGS__)
-#define ARCH_WARN_ASM(file, line, flags, size) \
- "1: twi 31, 0, 0\n" \
- _EMIT_BUG_ENTRY(2, 1b, file, line, flags) \
- ".org 2b+" size "\n" \
+#define ARCH_WARN_ASM(file, line, flags, size)
\
+ ARCH_WARN_ASM_TRAP_LABEL ": twi 31, 0, 0\n"
\
+ _EMIT_BUG_ENTRY(2, 1b, file, line, flags)
\
+ ".org 2b+" size "\n"
\
".previous\n"
#define ARCH_WARN_REACHABLE
diff --git a/arch/riscv/include/asm/bug.h b/arch/riscv/include/asm/bug.h
index 699c0cf3e4ef..def6b0d153f2 100644
--- a/arch/riscv/include/asm/bug.h
+++ b/arch/riscv/include/asm/bug.h
@@ -29,7 +29,8 @@
typedef u32 bug_insn_t;
-#define __BUG_ENTRY_ADDR RISCV_INT " 1b - ."
+#define ARCH_WARN_ASM_TRAP_LABEL "1"
+#define __BUG_ENTRY_ADDR RISCV_INT " " ARCH_WARN_ASM_TRAP_LABEL "b - ."
#define __BUG_ENTRY_FILE(file) RISCV_INT " " file " - ."
#ifdef CONFIG_DEBUG_BUGVERBOSE
@@ -47,7 +48,7 @@ typedef u32 bug_insn_t;
#ifdef CONFIG_GENERIC_BUG
#define ARCH_WARN_ASM(file, line, flags, size) \
- "1:\n\t" \
+ ARCH_WARN_ASM_TRAP_LABEL ":\n\t" \
"ebreak\n" \
".pushsection __bug_table,\"aw\"\n\t" \
"2:\n\t" \
diff --git a/arch/s390/include/asm/bug.h b/arch/s390/include/asm/bug.h
index 2010342c97b1..3c0fa1acc92a 100644
--- a/arch/s390/include/asm/bug.h
+++ b/arch/s390/include/asm/bug.h
@@ -26,9 +26,11 @@
#define WARN_CONDITION_STR(cond_str) ""
#endif
+#define ARCH_WARN_ASM_TRAP_LABEL "0"
+
#define __BUG_ENTRY(format, file, line, flags, size) \
" .section __bug_table,\"aw\"\n" \
- "1: .long 0b - . # bug_entry::bug_addr\n"\
+ "1: .long " ARCH_WARN_ASM_TRAP_LABEL "b - . #
bug_entry::bug_addr\n" \
" .long " format " - . # bug_entry::format\n" \
__BUG_ENTRY_VERBOSE(file, line) \
" .short "flags" # bug_entry::flags\n" \
diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index 23ab05438269..6cca8880660e 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -62,8 +62,9 @@ extern void __WARN_trap(struct bug_entry *bug, ...);
#define HAVE_ARCH_BUG_FORMAT_ARGS
#endif
+#define ARCH_WARN_ASM_TRAP_LABEL "1"
#define __BUG_ENTRY(format, file, line, flags) \
- "\t.long 1b - ." "\t# bug_entry::bug_addr\n" \
+ "\t.long " ARCH_WARN_ASM_TRAP_LABEL "b - ." "\t# bug_entry::bug_addr\n"
\
__BUG_ENTRY_FORMAT(format) \
__BUG_ENTRY_VERBOSE(file, line) \
"\t.word " flags "\t# bug_entry::flags\n"
@@ -101,7 +102,7 @@ do {
\
"99:\n" \
"\t.string \"\"\n" \
".popsection\n" \
- "1:\t " ASM_UD2 "\n" \
+ ARCH_WARN_ASM_TRAP_LABEL ":\t " ASM_UD2 "\n" \
_BUG_FLAGS_ASM("99b", file, line, flags, size, "")
#else
diff --git a/rust/Makefile b/rust/Makefile
index da1a7409d984..8f253d516495 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -46,7 +46,7 @@ obj-$(CONFIG_RUST_KERNEL_DOCTESTS) +=
doctests_kernel_generated_kunit.o
always-$(subst y,$(CONFIG_RUST),$(CONFIG_JUMP_LABEL)) +=
kernel/generated_arch_static_branch_asm.rs
ifndef CONFIG_UML
-always-$(subst y,$(CONFIG_RUST),$(CONFIG_BUG)) +=
kernel/generated_arch_warn_asm.rs kernel/generated_arch_reachable_asm.rs
+always-$(subst y,$(CONFIG_RUST),$(CONFIG_BUG)) +=
kernel/generated_arch_warn_asm.rs kernel/generated_arch_reachable_asm.rs
kernel/generated_arch_warn_asm_trap_label.rs
endif
# Avoids running `$(RUSTC)` when it may not be available.
diff --git a/rust/kernel/.gitignore b/rust/kernel/.gitignore
index f636ad95aaf3..05bb00bbb83c 100644
--- a/rust/kernel/.gitignore
+++ b/rust/kernel/.gitignore
@@ -3,3 +3,4 @@
/generated_arch_static_branch_asm.rs
/generated_arch_warn_asm.rs
/generated_arch_reachable_asm.rs
+/generated_arch_warn_asm_trap_label.rs
diff --git a/rust/kernel/Kconfig.test b/rust/kernel/Kconfig.test
index e6a5c7a795f0..8cd7c8f91b07 100644
--- a/rust/kernel/Kconfig.test
+++ b/rust/kernel/Kconfig.test
@@ -83,4 +83,19 @@ config RUST_BITFIELD_KUNIT_TEST
If unsure, say N.
+config RUST_BUG_WARN_ASM_KUNIT_TEST
+ bool "KUnit tests for ARCH_WARN_ASM bug table emission" if
!KUNIT_ALL_TESTS
+ depends on GENERIC_BUG && !ARM && !LOONGARCH && !UML
+ default KUNIT_ALL_TESTS
+ help
+ This option enables KUnit tests that verify ARCH_WARN_ASM emits a
+ correct __bug_table entry: the bug_addr displacement must resolve
+ back to the trap instruction so that find_bug() can locate the
+ entry — exactly as the real trap handler does.
+
+ Supported on all architectures that implement ARCH_WARN_ASM
+ (x86, powerpc, riscv, arm64, s390).
+
+ If unsure, say N.
+
endif
diff --git a/rust/kernel/bug.rs b/rust/kernel/bug.rs
index 3566f0234ca4..9e9b6d3a68b7 100644
--- a/rust/kernel/bug.rs
+++ b/rust/kernel/bug.rs
@@ -152,3 +152,194 @@ macro_rules! warn_on {
cond
}};
}
+
+// Test-only constants and file static referenced by the global_asm block
below.
+//
+// global_asm! is file-scope and always emitted — LLVM cannot eliminate it,
+// unlike asm! inside a function which is subject to dead-code removal.
+//
+// BUG_KUNIT_TRAP_ADDR is declared as a .global symbol entirely inside the
+// global_asm! block so the .dc.a {trap_label}b relocation lands directly on
it.
+// A Rust static initialized to zero would end up in BSS; the linker does
+// not apply relocations to BSS, so the address would stay zero at runtime.
+#[cfg(CONFIG_RUST_BUG_WARN_ASM_KUNIT_TEST)]
+mod test_statics {
+ use crate::bindings::{bug_entry, BUGFLAG_WARNING, TAINT_WARN};
+
+ pub(super) const FLAGS: u32 = BUGFLAG_WARNING | (TAINT_WARN << 8);
+ pub(super) const SIZE: usize = core::mem::size_of::<bug_entry>();
+
+ // LINE and BUG_KUNIT_FILE are only referenced by the {file}/{line}
+ // operands in global_asm!, which are only present when
+ // CONFIG_DEBUG_BUGVERBOSE is set (the non-verbose _EMIT_BUG_ENTRY
+ // drops the file/line fields from the bug table entry entirely).
+ #[cfg(CONFIG_DEBUG_BUGVERBOSE)]
+ pub(super) const LINE: u32 = line!();
+
+ // Null-terminated source file name — the assembler references this symbol
+ // for the verbose file pointer in __bug_table, same as warn_flags!.
+ #[cfg(CONFIG_DEBUG_BUGVERBOSE)]
+ const _FILE: &[u8] = file!().as_bytes();
+ #[cfg(CONFIG_DEBUG_BUGVERBOSE)]
+ #[no_mangle]
+ pub(super) static BUG_KUNIT_FILE: [u8; _FILE.len() + 1] = {
+ let mut bytes = [0u8; _FILE.len() + 1];
+ let mut i = 0;
+ while i < _FILE.len() {
+ bytes[i] = _FILE[i];
+ i += 1;
+ }
+ bytes
+ };
+}
+
+// Emit ARCH_WARN_ASM at file scope and capture the trap address.
+//
+// The asm string mirrors warn_flags!() exactly — same "/* {size} */" prefix,
+// same generated_arch_warn_asm.rs and generated_arch_reachable_asm.rs
includes,
+// same operands — so the two stay in sync as the macro evolves. The only
+// addition is the .pushsection/.dc.a/.popsection tail that records the trap
+// address into BUG_KUNIT_TRAP_ADDR at link time.
+//
+// BUG_KUNIT_TRAP_ADDR is a .global symbol in .data whose value is set by a
+// .dc.a relocation to the arch's trap label (from
+// generated_arch_warn_asm_trap_label.rs); .dc.a self-aligns to pointer width
+// so no .balign is needed.
+#[cfg(all(CONFIG_RUST_BUG_WARN_ASM_KUNIT_TEST, CONFIG_DEBUG_BUGVERBOSE))]
+::core::arch::global_asm!(
+ concat!(
+ "/* {size} */",
+ include!(concat!(env!("OBJTREE"),
"/rust/kernel/generated_arch_warn_asm.rs")),
+ include!(concat!(env!("OBJTREE"),
"/rust/kernel/generated_arch_reachable_asm.rs")),
+ "\n\t.pushsection .data\n\t",
+ ".global BUG_KUNIT_TRAP_ADDR\n\t",
+ "BUG_KUNIT_TRAP_ADDR:\n\t",
+ ".dc.a ",
+ include!(concat!(env!("OBJTREE"),
"/rust/kernel/generated_arch_warn_asm_trap_label.rs")),
+ "b\n\t",
+ ".popsection\n",
+ ),
+ file = sym test_statics::BUG_KUNIT_FILE,
+ line = const test_statics::LINE,
+ flags = const test_statics::FLAGS,
+ size = const test_statics::SIZE,
+);
+
+#[cfg(all(CONFIG_RUST_BUG_WARN_ASM_KUNIT_TEST, not(CONFIG_DEBUG_BUGVERBOSE)))]
+::core::arch::global_asm!(
+ concat!(
+ "/* {size} */",
+ include!(concat!(env!("OBJTREE"),
"/rust/kernel/generated_arch_warn_asm.rs")),
+ include!(concat!(env!("OBJTREE"),
"/rust/kernel/generated_arch_reachable_asm.rs")),
+ "\n\t.pushsection .data\n\t",
+ ".global BUG_KUNIT_TRAP_ADDR\n\t",
+ "BUG_KUNIT_TRAP_ADDR:\n\t",
+ ".dc.a ",
+ include!(concat!(env!("OBJTREE"),
"/rust/kernel/generated_arch_warn_asm_trap_label.rs")),
+ "b\n\t",
+ ".popsection\n",
+ ),
+ flags = const test_statics::FLAGS,
+ size = const test_statics::SIZE,
+);
+
+#[cfg(CONFIG_RUST_BUG_WARN_ASM_KUNIT_TEST)]
+#[::kernel::macros::kunit_tests(rust_kernel_bug_warn_asm)]
+mod tests {
+ use crate::bindings;
+
+ fn trap_addr() -> usize {
+ // BUG_KUNIT_TRAP_ADDR is a .global symbol defined in the global_asm!
+ // block above, placed in .data at the exact .dc.a 1b relocation word.
+ // The linker resolves it to the virtual address of the twi instruction
+ // before any Rust code runs, so reading it here is always safe.
+ extern "C" {
+ // .dc.a emits a pointer-width word: 4 bytes on ppc32, 8 on ppc64.
+ // usize matches the native pointer width on both.
+ static BUG_KUNIT_TRAP_ADDR: usize;
+ }
+ // SAFETY: read-only after link time, no concurrent mutation possible.
+ unsafe { BUG_KUNIT_TRAP_ADDR }
+ }
+
+ /// The `__bug_table` entry emitted by `ARCH_WARN_ASM` must be locatable
+ /// via `find_bug()` using the trap instruction's address. A NULL result
+ /// means the `1b` label reference in `_EMIT_BUG_ENTRY` resolved to the
+ /// wrong address and the real trap handler would not recognise the site.
+ #[test]
+ fn bug_entry_found() {
+ // Non-zero proves the .dc.a relocation was resolved by the linker.
+ assert!(trap_addr() != 0);
+
+ // SAFETY: find_bug() is always safe to call with any address; it
+ // simply walks __bug_table and returns NULL if nothing matches.
+ let entry = unsafe { bindings::find_bug(trap_addr()) };
+ // Non-NULL proves the bug_addr displacement in _EMIT_BUG_ENTRY is
correct.
+ assert!(!entry.is_null());
+ }
+
+ /// The emitted entry must be flagged as a warning (not a hard BUG).
+ #[test]
+ fn bug_entry_is_warning() {
+ assert!(trap_addr() != 0);
+ let entry = unsafe { bindings::find_bug(trap_addr()) };
+ assert!(!entry.is_null());
+ // SAFETY: entry is non-null and points to a valid bug_entry.
+ let flags = unsafe { (*entry).flags } as u32;
+ assert!(flags & bindings::BUGFLAG_WARNING != 0);
+ }
+
+ /// With `CONFIG_DEBUG_BUGVERBOSE` the entry must record a non-null file
+ /// pointer pointing back into this source file.
+ #[test]
+ #[cfg(CONFIG_DEBUG_BUGVERBOSE)]
+ fn bug_entry_file() {
+ use kernel::str::CStrExt;
+
+ assert!(trap_addr() != 0);
+ let entry = unsafe { bindings::find_bug(trap_addr()) };
+ assert!(!entry.is_null());
+
+ let mut file_ptr: *const kernel::ffi::c_char = core::ptr::null();
+ let mut line: u32 = 0;
+ // SAFETY: entry is non-null and valid; file_ptr and line are local
+ // variables passed as out-parameters.
+ unsafe { bindings::bug_get_file_line(entry, &mut file_ptr, &mut line)
};
+
+ assert!(!file_ptr.is_null());
+ // SAFETY: file_ptr is a non-null, null-terminated C string from
BUG_KUNIT_FILE,
+ // valid for the lifetime of this function.
+ let file_str = unsafe { kernel::prelude::CStr::from_char_ptr(file_ptr)
}
+ .to_str()
+ .unwrap_or("");
+ assert!(file_str.contains("bug"));
+ }
+
+ /// With `CONFIG_DEBUG_BUGVERBOSE` the recorded line number must be
+ /// non-zero (a zero line would mean the asm operand was not substituted).
+ #[test]
+ #[cfg(CONFIG_DEBUG_BUGVERBOSE)]
+ fn bug_entry_line() {
+ assert!(trap_addr() != 0);
+ let entry = unsafe { bindings::find_bug(trap_addr()) };
+ assert!(!entry.is_null());
+
+ let mut file_ptr: *const kernel::ffi::c_char = core::ptr::null();
+ let mut line: u32 = 0;
+ // SAFETY: entry is non-null and valid.
+ unsafe { bindings::bug_get_file_line(entry, &mut file_ptr, &mut line)
};
+
+ assert!(line != 0);
+ }
+
+ /// The trap address stored in `__bug_table` must lie within the kernel
+ /// text segment. If the label reference in `_EMIT_BUG_ENTRY` resolved
+ /// to data or zero, `kernel_text_address()` would return false.
+ #[test]
+ fn bug_entry_addr_is_in_text() {
+ assert!(trap_addr() != 0);
+ // SAFETY: kernel_text_address() is always safe to call with any addr.
+ let in_text = unsafe { bindings::kernel_text_address(trap_addr()) };
+ assert!(in_text != 0);
+ }
+}
diff --git a/rust/kernel/generated_arch_warn_asm_trap_label.rs.S
b/rust/kernel/generated_arch_warn_asm_trap_label.rs.S
new file mode 100644
index 000000000000..d7bed8751f10
--- /dev/null
+++ b/rust/kernel/generated_arch_warn_asm_trap_label.rs.S
@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include <linux/bug.h>
+
+// Cut here.
+
+::kernel::concat_literals!(ARCH_WARN_ASM_TRAP_LABEL)
--
2.55.0
