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linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, rust-for-linux@vger.kernel.org, llvm@lists.linux.dev Subject: Re: [RFC] rust: kernel: Add KUnit tests for ARCH_WARN_ASM bug table emission Message-ID: <20260924111557.GP1837346@noisy.programming.kicks-ass.net> References: <20260922054959.955093-2-mkchauras@gmail.com> <20260922064735.GS4121339@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org T24gV2VkLCBTZXAgMjMsIDIwMjYgYXQgMTE6NTg6MTNBTSArMDUzMCwgTXVrZXNoIEt1bWFyIENo YXVyYXNpeWEgd3JvdGU6Cj4gT24gVHVlLCBTZXAgMjIsIDIwMjYgYXQgMDg6NDc6MzVBTSArMDIw 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svens@linux.ibm.com, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, ojeda@kernel.org, boqun@kernel.org, gary@garyguo.net, bjorn3_gh@protonmail.com, lossin@kernel.org, a.hindborg@kernel.org, aliceryhl@google.com, tmgross@umich.edu, dakr@kernel.org, daniel.almeida@collabora.com, tamird@kernel.org, acourbot@nvidia.com, work@onurozkan.dev, nathan@kernel.org, ndesaulniers@google.com, morbo@google.com, justinstitt@google.com, jszhang@kernel.org, japo@linux.ibm.com, jpoimboe@kernel.org, seanjc@google.com, pmladek@suse.com, thuth@redhat.com, ynorov@nvidia.com, joelagnelf@nvidia.com, david@davidgow.net, fujita.tomonori@gmail.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, rust-for-linux@vger.kernel.org, llvm@lists.linux.dev Subject: Re: [RFC] rust: kernel: Add KUnit tests for ARCH_WARN_ASM bug table emission Message-ID: <20260924111557.GP1837346@noisy.programming.kicks-ass.net> References: <20260922054959.955093-2-mkchauras@gmail.com> <20260922064735.GS4121339@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Wed, Sep 23, 2026 at 11:58:13AM +0530, Mukesh Kumar Chaurasiya wrote: > On Tue, Sep 22, 2026 at 08:47:35AM +0200, Peter Zijlstra wrote: > > On Tue, Sep 22, 2026 at 11:20:00AM +0530, Mukesh Kumar Chaurasiya (IBM) wrote: > > > 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, > > > > > > > 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 > > > > Not really a fan of that. And I can't really tell what you're doing with > > it either. The kunit is in Rust and thus unreadable :-( > > > > I would rather you fix up is_valid_bugaddr(), some architectures seem to > > have an always true stub because of the callchains always being from the > > break instruction. > > Hey Peter, > > thanks for the suggestion. I will fix up the is_valid_bugaddr for > powerpc. I am not very good with other archs asm but i can do it for > ppc32 and ppc64. Untested thingies for arm64 and s390x. diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c index 914282016069..3d8a969eab5f 100644 --- a/arch/arm64/kernel/traps.c +++ b/arch/arm64/kernel/traps.c @@ -987,14 +987,13 @@ void do_serror(struct pt_regs *regs, unsigned long esr) #ifdef CONFIG_GENERIC_BUG int is_valid_bugaddr(unsigned long addr) { - /* - * bug_brk_handler() only called for BRK #BUG_BRK_IMM. - * So the answer is trivial -- any spurious instances with no - * bug table entry will be rejected by report_bug() and passed - * back to the debug-monitors code and handled as a fatal - * unexpected debug exception. - */ - return 1; + u32 insn; + + if (aarch64_insn_read((u32 *)addr, &insn)) + return 0; + + /* Match ASM_BUG_FLAGS() / BUG() instructions. */ + return insn == (0xd4200000 | (BUG_BRK_IMM << 5)); } #endif diff --git a/arch/s390/kernel/traps.c b/arch/s390/kernel/traps.c index b6ba4465f59d..8bbb082fd5e3 100644 --- a/arch/s390/kernel/traps.c +++ b/arch/s390/kernel/traps.c @@ -26,6 +26,7 @@ #include #include #include +#include #include #include #include @@ -55,7 +56,12 @@ static inline void __user *get_trap_ip(struct pt_regs *regs) #ifdef CONFIG_GENERIC_BUG int is_valid_bugaddr(unsigned long addr) { - return 1; + u16 insn; + + if (get_kernel_nofault(insn, (u16 *)addr)) + return 0; + + return insn == 0x0001 || insn == 0x000e; } #endif