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Donenfeld" , "Peter Zijlstra (Intel)" , "Theodore Ts'o" , =?UTF-8?Q?Thomas_Wei=C3=9Fschuh?= , Xin Li , Andrew Cooper , Andy Lutomirski , Ard Biesheuvel , Borislav Petkov , Brian Gerst , Dave Hansen , Ingo Molnar , James Morse , Jarkko Sakkinen , Josh Poimboeuf , Kees Cook , Nam Cao , Oleg Nesterov , Perry Yuan , Thomas Gleixner , Thomas Huth , Uros Bizjak , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-sgx@vger.kernel.org, x86@kernel.org, Indu Bhagat , Claudiu Zissulescu-Ianculescu , Heiko Carstens , Vasily Gorbik References: <20260106211856.560186-6-hpa@zytor.com> <223707e2-3231-4037-bd1f-490ddf6aeeb6@linux.ibm.com> Content-Language: en-US, sv-SE From: "H. Peter Anvin" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: A728E18000D X-Stat-Signature: hci6ie7ewqy9xk1qjnrtuzcdecetxnxt X-HE-Tag: 1770699167-823307 X-HE-Meta: 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 dUP5Vqmc VXtcvUnFAV23PWAD5U3JYS8wLWBgQlgnhmS6pO3rXThpt32U= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2026-02-09 19:11, Xi Ruoyao wrote: > On Mon, 2026-02-02 at 19:57 -0800, H. Peter Anvin wrote: >> That hack dates back from before the signal frame extension. It is no >> longer necessary. > > Unfortunately at least it seems libgcc unwinder does not handle the > signal frame extension properly. The code reads: > > fde = _Unwind_Find_FDE (context->ra + _Unwind_IsSignalFrame (context) - 1, > &context->bases); > if (fde == NULL) > { > #ifdef MD_FALLBACK_FRAME_STATE_FOR > /* Couldn't find frame unwind info for this function. Try a > target-specific fallback mechanism. This will necessarily > not provide a personality routine or LSDA. */ > return MD_FALLBACK_FRAME_STATE_FOR (context, fs); > #else > return _URC_END_OF_STACK; > #endif > } > > fs->pc = context->bases.func; > > cie = get_cie (fde); > insn = extract_cie_info (cie, context, fs); > > Thus, it indeed attempts to avoid subtracting 1 for a signal frame, but > ... _Unwind_IsSignalFrame (context) actually extracts a flag in context > which will only be raised up by extract_cie_info. > > Or am I missing something here? > Well, it looks like this might be a non-manifest bug on x86 *IN THIS CASE*, because the fallback handler looks explicitly for the byte sequences: popl %eax movl $__NR_ia32_sigreturn, %eax int $0x80 movl $__NR_ia32_rt_sigreturn, %eax int $0x80 movq $__NR_x64_rt_sigreturn, %rax /* !!!! */ syscall ... so the vdso patchset is still OK. Hard-coding a reliance on movq in the 64-bit sequence some serious brain damage... Could you file a gcc bug on this? -hpa