Multiple tools show duplicate-decl-specifier warning with clang 19

[jeromemarchand]

Multiple tools show the following warning when used with clang 19:

In file included from /virtual/main.c:14:
In file included from include/uapi/linux/ptrace.h:183:
In file included from arch/x86/include/asm/ptrace.h:175:
In file included from arch/x86/include/asm/paravirt_types.h:12:
In file included from arch/x86/include/asm/nospec-branch.h:15:
arch/x86/include/asm/current.h:47:10: warning: multiple identical address spaces specified for type [-Wduplicate-decl-specifier]
   47 |                 return this_cpu_read_const(const_pcpu_hot.current_task);
      |                        ^
arch/x86/include/asm/percpu.h:577:36: note: expanded from macro 'this_cpu_read_const'
  577 | #define this_cpu_read_const(pcp)                        __raw_cpu_read_const(pcp)
      |                                                         ^
arch/x86/include/asm/percpu.h:163:35: note: expanded from macro '__raw_cpu_read_const'
  163 | #define __raw_cpu_read_const(pcp)       __raw_cpu_read(, , pcp)
      |                                         ^
arch/x86/include/asm/percpu.h:155:30: note: expanded from macro '__raw_cpu_read'
  155 |         *(qual __my_cpu_type(pcp) *)__my_cpu_ptr(&(pcp));               \
      |                                     ^
note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
arch/x86/include/asm/percpu.h:94:40: note: expanded from macro '__my_cpu_type'
   94 | #define __my_cpu_type(var)      typeof(var) __percpu_seg_override
      |                                             ^
arch/x86/include/asm/percpu.h:45:32: note: expanded from macro '__percpu_seg_override'
   45 | # define __percpu_seg_override  __seg_gs
      |                                 ^
<built-in>:362:33: note: expanded from macro '__seg_gs'
  362 | #define __seg_gs __attribute__((address_space(256)))
      |                                 ^

The tools otherwise still work as expected. AFAICT, the issue lies in the kernel headers. A patch was posted upstream but haven't been taken yet: https://lore.kernel.org/all/[email protected]/

Applying this patch does indeed get rid of the warning.

[yonghong-song]

@jeromemarchand Thanks for the heads-up. The above commit has not merged yet and I have not tested bcc with latest 5.12/5.13 yet.

[JLT032]

unsure if this is related, just to mention this also seen with shmsnoop-bpfcc on Debian GNU/Linux 12 (bookworm) kernel

#shmsnoop-bpfcc
In file included from /virtual/main.c:2:
In file included from include/uapi/linux/ptrace.h:183:
In file included from arch/x86/include/asm/ptrace.h:175:
In file included from arch/x86/include/asm/paravirt_types.h:12:
In file included from arch/x86/include/asm/nospec-branch.h:15:
arch/x86/include/asm/current.h:47:10: warning: multiple identical address spaces specified for type [-Wduplicate-decl-specifier]
                return this_cpu_read_const(const_pcpu_hot.current_task);
                       ^
arch/x86/include/asm/percpu.h:577:36: note: expanded from macro 'this_cpu_read_const'
#define this_cpu_read_const(pcp)                        __raw_cpu_read_const(pcp)
                                                        ^
arch/x86/include/asm/percpu.h:163:35: note: expanded from macro '__raw_cpu_read_const'
#define __raw_cpu_read_const(pcp)       __raw_cpu_read(, , pcp)
                                        ^
arch/x86/include/asm/percpu.h:155:30: note: expanded from macro '__raw_cpu_read'
        *(qual __my_cpu_type(pcp) *)__my_cpu_ptr(&(pcp));               \
                                    ^
note: (skipping 1 expansions in backtrace; use -fmacro-backtrace-limit=0 to see all)
arch/x86/include/asm/percpu.h:94:40: note: expanded from macro '__my_cpu_type'
#define __my_cpu_type(var)      typeof(var) __percpu_seg_override
                                            ^
arch/x86/include/asm/percpu.h:45:32: note: expanded from macro '__percpu_seg_override'
# define __percpu_seg_override  __seg_gs
                                ^
<built-in>:329:33: note: expanded from here
#define __seg_gs __attribute__((address_space(256)))
                                ^