Re: [PATCH v4 11/11] perf auxtrace: Add compat_auxtrace_mmap__{read_head|write_tail}
From: "Russell King (Oracle)" <linux@armlinux.org.uk>
Date: 2021-07-12 14:44:59
Also in:
linux-arm-kernel, lkml
On Sun, Jul 11, 2021 at 06:41:05PM +0800, Leo Yan wrote:
When perf runs in compat mode (kernel in 64-bit mode and the perf is in 32-bit mode), the 64-bit value atomicity in the user space cannot be assured, E.g. on some architectures, the 64-bit value accessing is split into two instructions, one is for the low 32-bit word accessing and another is for the high 32-bit word.
Does this apply to 32-bit ARM code on aarch64? I would not have thought it would, as the structure member is a __u64 and compat_auxtrace_mmap__read_head() doesn't seem to be marking anything as packed, so the compiler _should_ be able to use a LDRD instruction to load the value. Is this a problem noticed on non-ARM architectures? Thanks. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!