[PATCH] csky: Implement _THIS_IP_ using inline asm

[Marco Elver <elver@google.com>]

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@roeck-us.net/ [3]
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Marco Elver <elver@google.com>
---
 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; })
+
+#endif /* __ASM_CSKY_LINKAGE_H */
-- 
2.56.0.rc1.315.gc6ed9934b7-goog