[Bug gold/26541] New: gold makes incorrect usage of fallocate in fallback path

[bugdal at aerifal dot cx]

https://sourceware.org/bugzilla/show_bug.cgi?id=26541

            Bug ID: 26541
           Summary: gold makes incorrect usage of fallocate in fallback
                    path
           Product: binutils
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gold
          Assignee: ccoutant at gmail dot com
          Reporter: bugdal at aerifal dot cx
                CC: ian at airs dot com
  Target Milestone: ---

In gold's output.cc gold_fallocate, after posix_fallocate() fails with a
non-fatal error, it tries fallocate(). However, the code assumes fallocate()
follows the same contract as posix_fallocate(), returning an error number,
rather than behaving as specified in the Linux man page for fallocate and
returning -1 with errno set to indicate the error. This makes EOPNOTSUPP into a
fatal error, since -1 is not equal EINVAL, ENOSYS, or EOPNOTSUPP.

This was likely overlooked because glibc's posix_fallocate (see
https://sourceware.org/bugzilla/show_bug.cgi?id=15661) has an unsafe emulation
in its own fallback path rather than returning EOPNOTSUPP to the caller.
However, it impacts other systems; the problem was reported to me by a musl
user on reiserfs, where fallocate is not implemented.

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