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Thu, 30 Oct 2025 08:30:34 +0100 Date: Thu, 30 Oct 2025 08:30:34 +0100 From: Jakub Jelinek To: Fangrui Song Cc: linux-toolchains@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: Concerns about SFrame viability for userspace stack walking Message-ID: Reply-To: Jakub Jelinek References: <3xd4fqvwflefvsjjoagytoi3y3sf7lxqjremhe2zo5tounihe4@3ftafgryadsr> Precedence: bulk X-Mailing-List: linux-toolchains@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3xd4fqvwflefvsjjoagytoi3y3sf7lxqjremhe2zo5tounihe4@3ftafgryadsr> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 On Wed, Oct 29, 2025 at 11:53:32PM -0700, Fangrui Song wrote: > I've been following the SFrame discussion and wanted to share some concerns about its viability for userspace adoption, based on concrete measurements and comparison with existing compact unwind implementations in LLVM. > > **Size overhead concerns** > > Measurements on a x86-64 clang binary show that .sframe (8.87 MiB) is approximately 10% larger than the combined size of .eh_frame and .eh_frame_hdr (8.06 MiB total). > This is problematic because .eh_frame cannot be eliminated - it contains essential information for restoring callee-saved registers, LSDA, and personality information needed for debugging (e.g. reading local variables in a coredump) and C++ exception handling. I believe .sframe only provides a subset of the .eh_frame information, so can't be used for exception throwing, and you don't want to lose .eh_frame_hdr either because then dlopen becomes very costly and it will even slow down exception throwing. If .eh_frame is considered too large, rather than inventing a new format I'd suggest to work in the DWARF committee and provide further size optimizations for .dwarf_frame which can then be used in .eh_frame, or agree on .eh_frame extensions to make it smaller. Jakub