[Bug binutils/27725] New: using -p in objcopy discards microseconds in destination timestamp

[rhbroberg at yahoo dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=27725

            Bug ID: 27725
           Summary: using -p in objcopy discards microseconds in
                    destination timestamp
           Product: binutils
           Version: 2.34
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: binutils
          Assignee: unassigned at sourceware dot org
          Reporter: rhbroberg at yahoo dot com
  Target Milestone: ---

It looks like the -p option to preserve timestamps only does it at the second
level, not at the microsecond level.  This causes issues in build systems which
have target objects linked, and then objcopy'd, and the end timestamp is
earlier than the original timestamp.  If any compilation unit was built in the
same second as the binary was linked, its timestamp will now be newer than the
resulting binary, and a subsequent build will re-link the binary as it
considers it to be out of date.

Here is a simple example on a ubuntu-20.04 machine running binutils/2.34:

rhb@ubuntu-20-04-01:/tmp$ ls -la --time-style=full-iso a.out
-rwxrwxr-x 1 rhb rhb 17320 2021-04-13 18:58:04.829559663 +0000 a.out
rhb@ubuntu-20-04-01:/tmp$ cp a.out a.out.withsymbols
rhb@ubuntu-20-04-01:/tmp$ objcopy -p --only-keep-debug a.out a.out.debuginfo
rhb@ubuntu-20-04-01:/tmp$ objcopy -p --strip-debug a.out
rhb@ubuntu-20-04-01:/tmp$ objcopy -p --add-gnu-debuglink=a.out.debuginfo a.out
rhb@ubuntu-20-04-01:/tmp$ ls -la --time-style=full-iso a.out*
-rwxrwxr-x 1 rhb rhb 17320 2021-04-13 18:58:04.000000000 +0000 a.out
-rwxrwxr-x 1 rhb rhb  5936 2021-04-13 18:58:04.000000000 +0000 a.out.debuginfo
-rwxrwxr-x 1 rhb rhb 17320 2021-04-13 18:59:15.131891948 +0000
a.out.withsymbols
rhb@ubuntu-20-04-01:/tmp$
rhb@ubuntu-20-04-01:/tmp$ apt list binutils
Listing... Done
binutils/focal-updates,focal-security,now 2.34-6ubuntu1.1 amd64
[installed,automatic]
N: There is 1 additional version. Please use the '-a' switch to see it
rhb@ubuntu-20-04-01:/tmp$

-----

Notice the timestamp of the created files have 0 as the microseconds timestamp.

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