[Bug c/46596] New: misbehavior when mixing always_inline and alias attributes in the same compilation unit

[Bug c/46596] New: misbehavior when mixing always_inline and alias attributes in the same compilation unit

[vapier at gentoo dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46596

           Summary: misbehavior when mixing always_inline and alias
                    attributes in the same compilation unit
           Product: gcc
           Version: 4.5.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: vapier@gentoo.org


i have a function "foo".  its header sets up an always_inline function that
does sanity checks when constants are involved.  otherwise it delays the
non-constant checking to another function.  here is the portion from the
header:
  extern void foo(int i);
  extern void __in(int i);
  extern inline __attribute__((always_inline))
  void foo(int i) { __in(i); }

where i actually define "foo", there is an alias used to setup multiple
symbols.  also in that file is another function which calls the inline checking
function.  together, gcc barfs.  here is the portion of the file:
  void bar(int i) { foo(i + 1234); }
  void __foo(int i) {}
  extern typeof(__foo) foo __attribute__((alias("__foo")));

combine them into one and compile like so (this is 4.5.1):
  gcc -O2 -c test.c -std=gnu99 -fgnu89-inline -Winline

this produces the error:
test.c: In function ‘bar’:
test.c:18:22: sorry, unimplemented: inlining failed in call to ‘foo’: function
body not available
test.c:14:5: sorry, unimplemented: called from here

that doesnt seem right since the function body *is* available.  if i split the
__foo/foo definitions into their own dedicated file, then everything compiles
just fine as i'd expect.

what's even more odd though is that -Winline affects code generation.  if you
compile without that flag, you dont get any errors, but the generated code is
wrong:
  gcc -O2 -c test.c -std=gnu99 -fgnu89-inline
  objdump -dr test.o
...
0000000000000000 <bar>:
   0:   81 c7 d2 04 00 00       add    $0x4d2,%edi
   6:   e9 00 00 00 00          jmpq   b <bar+0xb>
                        7: R_X86_64_PC32        foo-0x4
   b:   0f 1f 44 00 00          nopl   0x0(%rax,%rax,1)
...

clearly it's just jumping straight to the definition of foo rather than going
through the inline function.

doesnt seem to be a regression ... every gcc version ive tested fails in the
same way: 4.0.4, 4.1.2, 4.2.4, 4.3.5, 4.4.4, 4.5.1.  versions before 4.2.x had
the -fgnu89-inline flag dropped since that was the default behavior and so was
unnecessary (and unrecognized).

[Bug c/46596] misbehavior when mixing always_inline and alias attributes in the same compilation unit

[vapier at gentoo dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46596

--- Comment #1 from Mike Frysinger <vapier at gentoo dot org> 2010-11-22 03:49:52 UTC ---
Created attachment 22479
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=22479
example file

[Bug c/46596] misbehavior when mixing always_inline and alias attributes in the same compilation unit

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46596

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2010.11.22 11:08:59
                 CC|                            |hubicka at gcc dot gnu.org
     Ever Confirmed|0                           |1

--- Comment #2 from Richard Guenther <rguenth at gcc dot gnu.org> 2010-11-22 11:08:59 UTC ---
Confirmed.  That -Winline changes behavior is definitely a bug.

I'm not so sure about the rest, what probably happens is that the
later extern declaration overrides the former (but inherits the
always-inline attribute), removing the body.

What you seem to want is always inline foo(), but still have an
out-of-line copy that dispatches to __foo.  That seems - backward, no?

Complete testcase:

extern void __in(int i);
extern inline __attribute__((always_inline,gnu_inline))
void foo(int i) { __in(i); }
void bar(int i) { foo(i + 1234); }
void __foo(int i) { }
extern void foo(int i) __attribute__((alias("__foo")));

> ./cc1 -quiet /tmp/t.c  -O -Winline
/tmp/t.c: In function 'bar':
/tmp/t.c:6:13: sorry, unimplemented: inlining failed in call to 'foo': function
body not available
/tmp/t.c:4:22: sorry, unimplemented: called from here

expected: bar calls __in (i + 1234).

[Bug c/46596] misbehavior when mixing always_inline and alias attributes in the same compilation unit

[vapier at gentoo dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46596

--- Comment #3 from Mike Frysinger <vapier at gentoo dot org> 2010-11-22 18:51:09 UTC ---
i want to provide two symbols -- one that may be overridden and one that always
exists.  that's the point of having "__foo" be the normal symbol and "foo"
being the alias.  for people calling foo(), i want them to always use the
inline one to get the extra (but not required) checking.

[Bug c/46596] misbehavior when mixing always_inline and alias attributes in the same compilation unit

[jyasskin at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46596

Jeffrey Yasskin <jyasskin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jyasskin at gcc dot gnu.org

--- Comment #4 from Jeffrey Yasskin <jyasskin at gcc dot gnu.org> 2012-02-29 09:41:05 UTC ---
glibc runs into the "sorry, unimplemented" part of the issue, with
delta-reduced code like:

$ cat test.i
typedef __builtin_va_list __gnuc_va_list;
extern __inline __attribute__ ((__always_inline__)) __attribute__
((__artificial__)) void syslog (int __pri, const char *__fmt, ...) {
};
typedef __gnuc_va_list va_list;
void __syslog(int pri, const char *fmt, ...) {
}
extern __typeof (__syslog) syslog __attribute__ ((alias ("__syslog")));
void __vsyslog_chk(int pri, int flag, const char *fmt, va_list ap) {
  if (pri & ~(0x07|0x03f8)) {
    syslog(3|0x02|0x20|0x01,
           "syslog: unknown facility/priority: %x", pri);
  }
}
$ gcc -c -O2 -Winline test.i
test.i: In function ‘__vsyslog_chk’:
test.i:7:28: sorry, unimplemented: inlining failed in call to ‘syslog’:
function body not available
test.i:10:11: sorry, unimplemented: called from here

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.6.1/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro
4.6.1-9ubuntu3' --with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++,go --prefix=/usr
--program-suffix=-4.6 --enable-shared --enable-linker-build-id
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6
--libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-plugin
--enable-objc-gc --disable-werror --with-arch-32=i686 --with-tune=generic
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 4.6.1 (Ubuntu/Linaro 4.6.1-9ubuntu3) 


I haven't yet built a gcc from head to make sure the behavior is there without
Ubuntu's patches. The glibc problem was described at
http://plash.beasts.org/wiki/GlibcBuildIssues#head-b9149fbab065967691cf1bade23d84325c05e9b0
and reported at http://sourceware.org/bugzilla/show_bug.cgi?id=10375, but it
looks like a gcc problem to me.

[Bug c/46596] misbehavior when mixing always_inline and alias attributes in the same compilation unit

[hubicka at ucw dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46596

--- Comment #5 from Jan Hubicka <hubicka at ucw dot cz> 2012-02-29 15:07:18 UTC ---
> glibc runs into the "sorry, unimplemented" part of the issue, with
> delta-reduced code like:
> 
> $ cat test.i
> typedef __builtin_va_list __gnuc_va_list;
> extern __inline __attribute__ ((__always_inline__)) __attribute__
> ((__artificial__)) void syslog (int __pri, const char *__fmt, ...) {
> };
> typedef __gnuc_va_list va_list;
> void __syslog(int pri, const char *fmt, ...) {
> }
> extern __typeof (__syslog) syslog __attribute__ ((alias ("__syslog")));

The problem here seems to be that typeof copies always inline attribute.
GCC before version 4.7 do not see through aliases and thus it has always
inline function that is alias but it can not see the body.  So the message
is correct.

GCC 4.7 newly understands alaises, but this was major change of the internal
representation and can not be backported.  For older GCC, i think only
workaround
is to call __syslog instead of syslog or drop the idea of using always iline
here.  Extern inlines will be inlined anyway.

Honza

[Bug c/46596] misbehavior when mixing always_inline and alias attributes in the same compilation unit

[vapier at gentoo dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46596

Mike Frysinger <vapier at gentoo dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |toolchain at gentoo dot org
           See Also|                            |http://sourceware.org/bugzi
                   |                            |lla/show_bug.cgi?id=10375

--- Comment #6 from Mike Frysinger <vapier at gentoo dot org> 2012-02-29 16:13:44 UTC ---
(In reply to comment #4)

yes, the source of this bug was the glibc code which i reduced even further
into the testcase posted originally

(In reply to comment #5)

if gcc-4.7 works fine with the proposed code, then i'm fine with that.  we
already have workarounds in place for those.

[Bug ipa/46596] misbehavior when mixing always_inline and alias attributes in the same compilation unit

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=46596

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |luto at kernel dot org

--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 59197 has been marked as a duplicate of this bug. ***