[Bug gas/23153] New: gas: distinct input and output files are not properly detected on not-fully-emulated POSIX platforms

[pexu at sourceware dot mail.kapsi.fi]

https://sourceware.org/bugzilla/show_bug.cgi?id=23153

            Bug ID: 23153
           Summary: gas: distinct input and output files are not properly
                    detected on not-fully-emulated POSIX platforms
           Product: binutils
           Version: 2.31 (HEAD)
            Status: UNCONFIRMED
          Severity: critical
          Priority: P2
         Component: gas
          Assignee: unassigned at sourceware dot org
          Reporter: pexu at sourceware dot mail.kapsi.fi
  Target Milestone: ---

As of commit 67f846b59b32f3d704c601669409c2584383fea9 gas tries to use simple
heuristics to determine if the given input and output files are distinct (at
gas/as.c).

The files are stat()'d and then the `st_ino' members compared. The logic is
sound on 100% POSIX conforming platforms, however, the same cannot be said for
e.g. MinGW. MinGW uses a zero `st_ino' for any (existing) file (based on a
quick search this is by design, so not likely to change anytime soon). Thus, if
all input and output files exist, gas will spit out "The input and output files
must be distinct", which is not true.

As a funny side-effect, even if the input and output file are determined as
``non-distinct'', something within the GCC chain still removes the output file.
So, any even invocation will fail, while any odd invocation will succeed --
which is utterly confusing unless one takes a look at the source code and is
aware of the POSIX internals at some level.

Anyway, this commit effectively hinders any platform that does not supply an
unique `st_ino' for a given file. Given that gas has been working just fine
(and it ain't a filesystem utility), right out-of-the-box, for a long time
without this, be it a native or a cross-compiling build, I see that this commit
causes much, much more harm than good.

(Cygwin is not affected by this, as it appears to emulate an unique `st_ino'.)

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