[Bug 250872] objcopy (elfcopy, elftoolchain) in-place operation emits output to wrong filesystem

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=250872

            Bug ID: 250872
           Summary: objcopy (elfcopy, elftoolchain) in-place operation
                    emits output to wrong filesystem
           Product: Base System
           Version: CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: bin
          Assignee: bugs at FreeBSD.org
          Reporter: cem at freebsd.org

objcopy can fail with 'write failed: No space left on device' when working on a
file in a filesystem with tons of free space.  (I.e., no explicit destination
file, dst == src.)

This is because create_tempfile() is completely ignorant of any destination
goal and writes everything to /tmp.  Then, for files outside of /tmp,
copy_from_tempfile() cannot rely on rename(2) putting the output in place of
the input file and has to instead do a full read-copy-write from /tmp.

For "temporary" files which are really the work-in-progress output file, they
should be emitted to the destination directory and renamed over the top of the
destination file.  I'd suggest:

1. Add an optional destination path parameter to create_tempfile. 
create_file() passes src in 'dst == NULL' case near top of function, and
possibly for other consumers in the same file if they are potentially the final
output file.

2. create_tempfile constructs a path adjacent to 'src' (that doesn't exist
already) and opens it, if src is provided.  Otherwise, it uses its existing
logic to construct a temporary file in /tmp.

3. The rest of the logic in create_file / copy_from_tempfile should handle this
correctly already.

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