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Peter Anvin" To: Uros Bizjak , Alexey Makhalov Cc: "Jason A. 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 , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-sgx@vger.kernel.org, x86@kernel.org References: <20251112043730.992152-1-hpa@zytor.com> <20251112043730.992152-8-hpa@zytor.com> Content-Language: en-US, sv-SE In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: E3ABF4000E X-Stat-Signature: nu6bzgut67dugh79c5o6wd3ftbamsgcb X-Rspam-User: X-HE-Tag: 1763154586-348074 X-HE-Meta: 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 Sah388I2 2hpVCw0wQLfY2suMoPqlD9QpUPF2tqxa8lV/y7c4C3XUJdRkJiouyuHOBjbUcxbtQs67SBnrRb0WyM5QM4rwfnfC7PSq1kkbKSJ+clS2VarstLeMDf07vIm0pFT+1kAkrQ/pCiYfq4eAs1TbY1HraAZlVzD7x6gbY4nMvs+gx0SUlOzJuv0Y+kxkJh4sTuGxm6lngKW5+ckOj/yfozvi3oHJaOn61E6IQngzx5Oz+2Kfv6uMqj0oLBJnUfVjpU4OPHdsgeD3l2n4t0f8zkHc6TnDwQ2zEZw20Yekv0MAji8FcSX2xY6HDgcP6Jg/i7dj2rirMvYCwS0xiJvEkOB4nxYQumw== 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 2025-11-13 20:40, H. Peter Anvin wrote: > > For 64 bits, if you need frame pointer support *and* frob %rsp, using: > > xchg %[arg],%%rbp > > xchg %[arg],%%rbp > > ... is probably easiest, with %[arg] in a register. > Incidentally, ORC is one thing, but if you need DWARF information to be correct for user space, it is definitely "fun". With the xchg hack for 64 bits it is just a matter of using .cfi_def_cfa_register to change the frame pointer around, but in the 32-bit case the best I could come up with was: .cfi_remember_state push %ebp .cfi_escape 0x0f,3,0x74,0,0x06 // CFA address in *%esp mov %eax, %ebp mov $syscall_no, %eax int $0x80 pop %ebp .cfi_restore_state Note that in both cases you need to *NOT* put in any of these CFI directives when compiling without frame pointers (in which case you need to let gcc take care of it if you want any hope of getting the CFI correct.) -hpa