[Bug libc/31968] New: mremap implementation in C does not handle arguments correctly

["fweimer at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=31968

            Bug ID: 31968
           Summary: mremap implementation in C does not handle arguments
                    correctly
           Product: glibc
           Version: 2.35
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: fweimer at redhat dot com
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

Conditional varargs processing for system calls is bad.  It causes an ongoing
maintenance headache, and weird application issues.  For example, Linux 5.7
added MREMAP_DONTUNMAP, and it can use the address argument just like
MREMAP_FIXED.  But the current mremap implementation always passes NULL as a
system call argument.

Regression in 2.35 caused by:

commit 5b3e31e3124bf89710e5c25176c70fdf66c2a212
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Wed Jun 17 09:29:07 2020 -0300

    linux: Implement mremap in C

    Variadic function calls in syscalls.list does not work for all ABIs
    (for instance where the argument are passed on the stack instead of
    registers) and might have underlying issues depending of the variadic
    type (for instance if a 64-bit argument is used).

    Checked on x86_64-linux-gnu.

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