* Maciej W. Rozycki:
On Thu, 6 Dec 2018, Joseph Myers wrote:
So how are `SYS_<name>' macros generated that land in <bits/syscall.h>?
By gen-syscall-h.awk, which generates #ifdef conditionals for each possible __NR_* name (as listed in syscall-names.list in glibc).
I seem to remember having to take extra care with how the three MIPS ABIs wire the syscalls to get it right in glibc, but I take it then this has been now addressed reliably enough for the glibc not to care how exactly <asm/unistd.h> has been arranged.
This is a fairly recent change (commit 2dba5ce7b8115d6a2789bf279892263621088e74, "<bits/syscall.h>: Use an arch-independent system call list on Linux", first release with it is glibc 2.27). This patch is quite backportable; we have put it into our 2.17-derived glibc, and the upstream work was originally driven by downstream ordering requirements of kernel header and glibc builds. Glad to see it's useful elsewhere.
The test retains the old <asm/unistd.h>-based macro extraction for testing purposes, but it needs that only for the actual target architecture and only the *names*, so it's easy to implement. Before that, the generation would have to carefully take into account multiple sub-targets (i386/x86-64/x32 is one of the more complicated scenarios). Presumably, you saw problem with that part.
Even if you introduce breakage here, it will only affect older glibc builds. It's not something that application developers would see.
Thanks, Florian