https://lwn.net/Articles/604515/ This is a special feed containing comments posted to the individual LWN article titled "Anatomy of a system call, part 2". en-us Tue, 21 Oct 2025 22:48:03 +0000 Tue, 21 Oct 2025 22:48:03 +0000 https://www.rssboard.org/rss-specification lwn@lwn.net https://lwn.net/Articles/635604/ https://lwn.net/Articles/635604/ drysdale <p>One additional detail to point out for the x32 ABI case: the syscall number gets a high bit set (<a href="http://lxr.free-electrons.com/source/arch/x86/include/uapi/asm/unistd.h?v=3.14#L5"><tt>__X32_SYSCALL_BIT</tt></a>), to mark it as an x32 call. <p> If x32 support is included in the kernel, then <a href="http://lxr.free-electrons.com/source/arch/x86/include/asm/unistd.h?v=3.14#L8"><tt>__SYSCALL_MASK</tt></a> will have a value that is not all-ones, and this will trigger an extra instruction in <tt>system_call</tt> to <a href="http://lxr.free-electrons.com/source/arch/x86/kernel/entry_64.S?v=3.14#L621">mask off</a> the extra bit, so that the syscall table indexing still works. Thu, 05 Mar 2015 17:04:52 +0000