[v3] libio: do not unbuffer legacy standard files in compatibility mode [BZ #24228]
Commit Message
On Wed, Jun 19, 2019 at 06:15:06PM +0200, Florian Weimer wrote:
> * Dmitry V. Levin:
> > On Wed, Jun 19, 2019 at 03:10:14PM +0200, Florian Weimer wrote:
> >> * Dmitry V. Levin:
> >>
> >> > 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
> >> > if (! (fp->_flags & _IO_UNBUFFERED)
> >> > /* Iff stream is un-orientated, it wasn't used. */
> >> > && fp->_mode != 0)
> >>
> >> I believe a better fix would be this, in case an old-style file showed
> >> up for a different reason:
> >>
> >> #if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_1)
> >> bool potentially_wide_stream = _IO_vtable_offset (fp) != 0;
> >> #else
> >> bool potentially_wide_stream = true;
> >> #endif
> >> if (potentially_wide_stream && fp->_mode > 0)
> >> _IO_wsetb (fp, NULL, NULL, 0);
> >>
> >> This is _IO_new_fclose handles this situation.
> >
> > Yes, this approach seems to work, too:
> >
> > diff --git a/libio/genops.c b/libio/genops.c
> > index 2a0d9b81df..575f0e6584 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_vtable_offset (fp) != 0))
> > + continue;
> > +#endif
> > if (! (fp->_flags & _IO_UNBUFFERED)
> > /* Iff stream is un-orientated, it wasn't used. */
> > && fp->_mode != 0)
>
> Hmm, right there's an early access to fp->_mode that I had missed.
> Should we still flush buffers in old binaries?
>
> I think we could do this instead:
>
> int mode;
> #if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_1)
> if (__glibc_unlikely (_IO_vtable_offset (fp) != 0))
> mode = 1; /* Old streams are never wide. */
> else
> mode = fp->_mode;
> #else
> mode = fp->_mode;
> #endif
>
> And then use mode instead of fp->_mode below. Does this make sense?
_mode is not the only member that is not available in legacy libio,
_freeres_list and _freeres_buf also should be avoided.
Would you prefer the following approach?
Comments
* Dmitry V. Levin:
> _mode is not the only member that is not available in legacy libio,
> _freeres_list and _freeres_buf also should be avoided.
> Would you prefer the following approach?
>
> diff --git a/libio/genops.c b/libio/genops.c
> index 2a0d9b81df..11a15549e8 100644
> --- a/libio/genops.c
> +++ b/libio/genops.c
> @@ -789,9 +789,16 @@ _IO_unbuffer_all (void)
>
> for (fp = (FILE *) _IO_list_all; fp; fp = fp->_chain)
> {
> + int legacy = 0;
> +
> +#if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_1)
> + if (__glibc_unlikely (_IO_vtable_offset (fp) != 0))
> + legacy = 1;
> +#endif
This approach looks reasonable to me. It's certainly much better than
what we have today. If you post a full patch, I'll test it against
one of the problematic OpenJDK 8 builds.
@@ -789,9 +789,16 @@ _IO_unbuffer_all (void)
for (fp = (FILE *) _IO_list_all; fp; fp = fp->_chain)
{
+ int legacy = 0;
+
+#if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_1)
+ if (__glibc_unlikely (_IO_vtable_offset (fp) != 0))
+ legacy = 1;
+#endif
+
if (! (fp->_flags & _IO_UNBUFFERED)
/* Iff stream is un-orientated, it wasn't used. */
- && fp->_mode != 0)
+ && (legacy || fp->_mode != 0))
{
#ifdef _IO_MTSAFE_IO
int cnt;
@@ -805,7 +812,7 @@ _IO_unbuffer_all (void)
__sched_yield ();
#endif
- if (! dealloc_buffers && !(fp->_flags & _IO_USER_BUF))
+ if (! legacy && ! dealloc_buffers && !(fp->_flags & _IO_USER_BUF))
{
fp->_flags |= _IO_USER_BUF;
@@ -816,7 +823,7 @@ _IO_unbuffer_all (void)
_IO_SETBUF (fp, NULL, 0);
- if (fp->_mode > 0)
+ if (! legacy && fp->_mode > 0)
_IO_wsetb (fp, NULL, NULL, 0);
#ifdef _IO_MTSAFE_IO
@@ -827,7 +834,8 @@ _IO_unbuffer_all (void)
/* Make sure that never again the wide char functions can be
used. */
- fp->_mode = -1;
+ if (! legacy)
+ fp->_mode = -1;
}
#ifdef _IO_MTSAFE_IO