[Bug libc/27508] New: expose a variadic form of syscall, by analogy with vprintf, vscanf, and verr

[Bug libc/27508] New: expose a variadic form of syscall, by analogy with vprintf, vscanf, and verr

[dkg at fifthhorseman dot net]

https://sourceware.org/bugzilla/show_bug.cgi?id=27508

            Bug ID: 27508
           Summary: expose a variadic form of syscall, by analogy with
                    vprintf, vscanf, and verr
           Product: glibc
           Version: unspecified
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: dkg at fifthhorseman dot net
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

In some circumstances, a variadic function might want to invoke `syscall` with
its variadic arguments.

To do this cleanly, we'd need glibc to export a variadic variant of `syscall`,
by analogy with `vprintf`, `verr`, and `vscanf`.

For contrived usage example, consider some code that tries to dispatch a
variadic function call either to some internal implementation or to a syscall:

#define SYSCALL_NUMBER XXXX
int foo(handler_t handler, ...) {
 va_list ap;
 va_start(ap, handler);
 if (handler == HANDLER_INTERNAL) {
   handle_internally(ap);
 else if (handler == HANDLE_SYSCALL) {
   vararg_syscall(SYSCALL_NUMBER, ap);
 }
}


If you want a non-contrived example, this has come up for `faketime`, which is
used for intercepting/bypassing some time-specific low-level functionality:

   https://github.com/wolfcw/libfaketime/issues/176

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