syscalls: normalize _exit(2) declerations

exit(3) is implemented by the runtime and performs a number of shutdown
actions before ultimately calling _exit(2) to terminate the program.  We
historically named the syscall table entry `exit` rather than `_exit`,
but this requires special handling in libc/libsys to cause the `_exit`
symbol to exist while implementing `exit` in libc.

Declare the syscall as `_exit` and flow that through the system.

Because syscall(SYS_exit, code) is fairly widely used, allow a
configured extra line in syscall.h to define SYS_exit to SYS__exit.

I've found no external uses of __sys_exit() so I've not bothered to
create a compatability version of this private symbol.

Reviewed by:	imp, kib, emaste
Differential Revision:	https://reviews.freebsd.org/D51672

1 files changed, 4 insertions, 0 deletions

diff --git a/sys/tools/syscalls/scripts/syscall_h.lua b/sys/tools/syscalls/scripts/syscall_h.lua
index 5f8d8fb66889..d05a1799935b 100755
--- a/sys/tools/syscalls/scripts/syscall_h.lua
+++ b/sys/tools/syscalls/scripts/syscall_h.lua
@@ -38,6 +38,10 @@ function syscall_h.generate(tbl, config, fh)
 	-- Write the generated preamble.
 	gen:preamble("System call numbers.")
 
+	if config.syshdr_extra then
+		gen:write(string.format("%s\n\n", config.syshdr_extra))
+	end
+
 	for _, v in pairs(s) do
 		local c = v:compatLevel()
 		if v.num > max then