Re: [PATCH] csky: Implement _THIS_IP_ using inline asm

[David Laight]

On Sun, 27 Sep 2026 10:15:11 +0800
Guo Ren <guoren@xxxxxxxxxx> wrote:

> On Fri, Sep 25, 2026 at 7:51 PM Marco Elver <elver@xxxxxxxxxx> wrote:
> >
> > Both GCC [1] and Clang [2] consider the generic version of _THIS_IP_ to
> > be broken:
> >
> >         #define _THIS_IP_  ({ __label__ __here; __here: (unsigned long)&&__here; })
> >
> > In particular, the address of a label is only expected to be used with a
> > computed goto.
> >
> > While the generic version more or less works today, it is known to be
> > brittle and may break with current and future optimizations. 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; }); }
> >
> > Fix it by overriding _THIS_IP_ in <asm/linkage.h> (which is included by
> > <linux/instruction_pointer.h>) using an architecture-specific inline asm
> > version.
> >
> > This also fixes this GCC ICE [3]:
> >
> > 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
> >
> > Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120071 [1]
> > Link: https://github.com/llvm/llvm-project/issues/138272 [2]
> > Link: https://lore.kernel.org/all/6106aefa-47c7-4bda-a51f-8a2fba3bf715@xxxxxxxxxxxx/ [3]
> > Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
> > ---
> >  arch/csky/include/asm/linkage.h | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >  create mode 100644 arch/csky/include/asm/linkage.h
> >
> > diff --git a/arch/csky/include/asm/linkage.h b/arch/csky/include/asm/linkage.h
> > new file mode 100644
> > index 000000000000..04afd3583e25
> > --- /dev/null
> > +++ b/arch/csky/include/asm/linkage.h
> > @@ -0,0 +1,7 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef __ASM_CSKY_LINKAGE_H
> > +#define __ASM_CSKY_LINKAGE_H
> > +
> > +#define _THIS_IP_ ({ unsigned long __ip; asm volatile("grs %0, ." : "=r" (__ip)); __ip; })  
> 
> Yes, this is the right fix.

Possibly "grs %0, 0" would be less obtuse.
I think "grs reg, label" is documented as being "grs reg, (label - .) >> 1".
The doc I found has some strange translations in it, grs is "Generate sign".

David

> 
> csky has always used the generic label-address _THIS_IP_.  That is
> brittle, and on csky the compiler now crashes when that address is
> folded into an immediate.  `grs rz, .` materializes the current
> instruction address, so it is the correct replacement.
> 
> Acked-by: GUO Ren (XuanTie) <guoren@xxxxxxxxxx>
> 
> 
> > +
> > +#endif /* __ASM_CSKY_LINKAGE_H */
> > --
> > 2.56.0.rc1.315.gc6ed9934b7-goog
> >  
> 
>