Re: csky ICe (was: Re: [PATCH v4 2/3] slab: improve KMALLOC_PARTITION_RANDOM randomness)

[Mike Rapoport <rppt@kernel.org>]

On Tue, Sep 22, 2026 at 07:58:56AM -0700, Guenter Roeck wrote:
> Hi,
> 
> On Mon, May 11, 2026 at 10:00:49PM +0200, Marco Elver wrote:
> > When using CONFIG_KMALLOC_PARTITION_RANDOM, _RET_IP_ was previously used
> > to identify the allocation site. _RET_IP_, however, evaluates to the
> > caller's parent's instruction pointer rather than the actual allocation
> > site; this would lead to collisions where a function performs multiple
> > allocations.
> > 
> > With the generalization to kmalloc_token_t, we now generate the token at
> > the outermost macro, and using _THIS_IP_ would fix this for all cases.
> > 
> > Unfortunately, the generic implementation of _THIS_IP_ relies on taking
> > the address of a local label, which is considered broken by both GCC [1]
> > and Clang [2] because label addresses are only expected to be used with
> > computed gotos. While the generic version more or less works today, it
> > is known to be brittle. For example, Clang -O2 always returns 1 when
> > this function is inlined:
> > 
> >         static inline unsigned long get_ip(void)
> >         { return ({ __label__ __here; __here: (unsigned long)&&__here; }); }
> > 
> > To provide a reliable unique identifier without breaking architectures
> > relying on the generic _THIS_IP_, introduce _CODE_LOCATION_: it resolves
> > to _THIS_IP_ where architectures provide a safe implementation, and
> > falls back to a zero-cost static marker where _THIS_IP_ is broken.
> > 
> > Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120071 [1]
> > Link: https://github.com/llvm/llvm-project/issues/138272 [2]
> > Signed-off-by: Marco Elver <elver@google.com>
> 
> With this patch in the tree, I get ICE erors when trying to build
> csky:allmodconfig.
> 
> Example:
> 
> Error log:
> sound/core/oss/mixer_oss.c: In function 'snd_mixer_oss_proc_write':
> sound/core/oss/mixer_oss.c:1202:1: error: could not split insn
>  1202 | }
>       | ^
> (insn 183 400 184 (set (reg:SI 0 a0 [orig:307 _55 ] [307])
>         (xor:SI (reg:SI 3 a3 [orig:308 random_kmalloc_seed ] [308])
>             (const:SI (plus:SI (symbol_ref:SI ("*.LANCHOR0") [flags 0x182])
>                     (const_int 132 [0x84]))))) "include/linux/slab.h":759:52 288 {cskyv2_xorsi3}
>      (expr_list:REG_DEAD (reg:SI 3 a3 [orig:308 random_kmalloc_seed ] [308])
>         (nil)))
> during RTL pass: final
> sound/core/oss/mixer_oss.c:1202:1: internal compiler error: in final_scan_insn_1, at final.cc:2813
> 0x779b51e2a1c9 __libc_start_call_main
> 	../sysdeps/nptl/libc_start_call_main.h:58
> 0x779b51e2a28a __libc_start_main_impl
> 	../csu/libc-start.c:360
> 
> This happens with lots of files, not just this one. It is seen with all
> versions of gcc starting with at least v13.x. Reverting this patch fixes
> the problem. Bisect log is attached for reference.
> 
> Any idea what I could do to avoid the problem other than stopping to build
> csky:allmodconfig ?

Maybe it's time to say goodbye to csky? ;-)
 
> Thanks,
> Guenter

-- 
Sincerely yours,
Mike.