Re: [PATCH v1 1/1] bpf: Disable -Wsuggest-attribute=format

[Ihor Solodrai <ihor.solodrai@linux.dev>]

On 12/15/25 4:11 PM, Ihor Solodrai wrote:
> On 12/10/25 5:12 AM, Andy Shevchenko wrote:
>> [...]
>> -obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o log.o token.o liveness.o
>> +obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o tnum.o log.o token.o liveness.o
>> +
>> +obj-$(CONFIG_BPF_SYSCALL) += helpers.o stream.o
>> +# The ____bpf_snprintf() uses the format string that triggers a compiler warning.
>> +CFLAGS_helpers.o += -Wno-suggest-attribute=format
>> +# The bpf_stream_vprintk_impl() uses the format string that triggers a compiler warning.
>> +CFLAGS_stream.o += -Wno-suggest-attribute=format
> 
> Hi Andy,
> 
> This flag does not exist in clang:
> 
> $ LLVM=1 make -j$(nproc) 
>   [...]
> $ LLVM=1 make
>   CALL    scripts/checksyscalls.sh
>   DESCEND objtool
>   INSTALL libsubcmd_headers
>   DESCEND bpf/resolve_btfids
>   INSTALL libsubcmd_headers
>   CC      kernel/trace/bpf_trace.o
> error: unknown warning option '-Wno-suggest-attribute=format'; did you mean '-Wno-property-attribute-mismatch'? [-Werror,-Wunknown-warning-option]
> make[4]: *** [scripts/Makefile.build:287: kernel/trace/bpf_trace.o] Error 1
> make[3]: *** [scripts/Makefile.build:556: kernel/trace] Error 2
> make[2]: *** [scripts/Makefile.build:556: kernel] Error 2
> make[1]: *** [/home/isolodrai/kernels/bpf-next/Makefile:2030: .] Error 2
> make: *** [Makefile:248: __sub-make] Error 2
> 
> We should probably conditionalize the flag addition in the makefile.

Just confirmed that the patch below fixes LLVM=1 build:

From 842b31ff3384df65bb6f13763464daa03ba4f025 Mon Sep 17 00:00:00 2001
From: Ihor Solodrai <isolodrai@meta.com>
Date: Mon, 15 Dec 2025 16:45:19 -0800
Subject: [PATCH] bpf: Ensure CC is set to GCC for
 -Wno-suggest-attribute=format

LLVM=1 kernel build got broken because clang does not have
-Wno-suggest-attribute=format option.

Check for CONFIG_CC_IS_GCC before setting this option.

Fixes: ba34388912b5 ("bpf: Disable false positive -Wsuggest-attribute=format warning")
Closes: https://lore.kernel.org/bpf/20251210131234.3185985-1-andriy.shevchenko@linux.intel.com/
Signed-off-by: Ihor Solodrai <isolodrai@meta.com>
---
 kernel/bpf/Makefile   | 2 ++
 kernel/trace/Makefile | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index d7bcdb1fd35a..7a33c701e5fb 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -17,8 +17,10 @@ obj-$(CONFIG_BPF_JIT) += trampoline.o
 obj-$(CONFIG_BPF_SYSCALL) += btf.o memalloc.o rqspinlock.o stream.o
 # Disable incorrect warning. bpf printf-like helpers cannot use
 # gnu_printf attribute.
+ifeq ($(CONFIG_CC_IS_GCC),y)
 CFLAGS_helpers.o += -Wno-suggest-attribute=format
 CFLAGS_stream.o += -Wno-suggest-attribute=format
+endif
 ifeq ($(CONFIG_MMU)$(CONFIG_64BIT),yy)
 obj-$(CONFIG_BPF_SYSCALL) += arena.o range_tree.o
 endif
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index 5869c1f1af89..06705d6fed2c 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -90,7 +90,9 @@ obj-$(CONFIG_USER_EVENTS) += trace_events_user.o
 obj-$(CONFIG_BPF_EVENTS) += bpf_trace.o
 # Disable incorrect warning. bpf printf-like helpers cannot use
 # gnu_printf attribute.
+ifeq ($(CONFIG_CC_IS_GCC),y)
 CFLAGS_bpf_trace.o += -Wno-suggest-attribute=format
+endif
 obj-$(CONFIG_KPROBE_EVENTS) += trace_kprobe.o
 obj-$(CONFIG_TRACEPOINTS) += error_report-traces.o
 obj-$(CONFIG_TRACEPOINTS) += power-traces.o
-- 
2.47.3

> 
> Or better yet, address the root cause as suggested in the thread.
> 
> BPF CI is red on bpf branch at the moment:
> https://github.com/kernel-patches/bpf/actions/runs/20243520506/job/58144348281
> 
>>
>>  [...]
>