[PATCH v3] libio: do not unbuffer legacy standard files in compatibility mode [BZ #24228]

[Dmitry V. Levin]

On Wed, Mar 13, 2019 at 04:08:16PM +0100, Florian Weimer wrote:
> * Dmitry V. Levin:
> 
> > Commit glibc-2.23~693 (a601b74d31ca086de38441d316a3dee24c866305)
> 
> Please quote the commit hash and commit subject, kernel-style.

The kernel-style reference would look this way:

Commit a601b74d31ca ("In preparation for fixing BZ#16734, fix failure in
misc/tst-error1-mem when _G_HAVE_MMAP is turned off.")

I'd like to add a reference to glibc-2.23~693 somewhere because
I find it useful, but I don't see any suitable place for it
in this long kernel-style form.

> (How did you determine this reference, anyway?)

Sorry?

> > diff --git a/libio/genops.c b/libio/genops.c
> > index 2a0d9b81df..aa92d61b6b 100644
> > --- a/libio/genops.c
> > +++ b/libio/genops.c
> > @@ -789,6 +789,10 @@ _IO_unbuffer_all (void)
> >  
> >    for (fp = (FILE *) _IO_list_all; fp; fp = fp->_chain)
> >      {
> > +#if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_1)
> > +      if (__glibc_unlikely (&_IO_stdin_used == NULL) && _IO_legacy_file (fp))
> > +	continue;
> > +#endif
> 
> I wonder if we should check _IO_legacy_file only here.  This is related
> to the previous discussion.

If we omitted the check for _IO_stdin_used, then standard files
would be skipped and misc/tst-error1-mem would complain.

> > diff --git a/libio/tst-bz24228.c b/libio/tst-bz24228.c
> > new file mode 100644
> > index 0000000000..3692f14b71
> > --- /dev/null
> > +++ b/libio/tst-bz24228.c
> > @@ -0,0 +1,30 @@
> > +/* BZ #24228 check for memory corruption in legacy libio
> > +
> > +   Copyright (C) 2019 Free Software Foundation, Inc.
> > +   This file is part of the GNU C Library.
> 
> We do not generally have a blank line for the “Copyright” line, I think.

No problem, I can remove it.
I don't think we are quite consistent about it, though.

> > +#include <mcheck.h>
> > +#include <support/test-driver.h>
> > +
> > +static int
> > +do_test (void)
> > +{
> > +  mtrace ();
> > +  return 0;
> > +}
> > +
> > +#include <support/test-driver.c>
> > diff --git a/libio/tst-bz24228.map b/libio/tst-bz24228.map
> > new file mode 100644
> > index 0000000000..ecb8c058f5
> > --- /dev/null
> > +++ b/libio/tst-bz24228.map
> > @@ -0,0 +1,3 @@
> > +{
> > +  local: _IO_stdin_used;
> > +};
> 
> Please add a comment to the file why you are doing this, something like
> “hide the symbol from libc.so.6 to switch to the libio/oldfileops.c
> implementation (if it is available for the architecture)”.

Indeed, thanks for the suggestion.


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