linux-kernel - [PATCH] bpf: fix check against plain integer v 'NULL'

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Message-Id: <20220714100322.260467-1-ben.dooks@sifive.com>
Date:   Thu, 14 Jul 2022 11:03:22 +0100
From:   Ben Dooks <ben.dooks@...ive.com>
To:     linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Cc:     Sudip Mukherjee <sudip.mukherjee@...ive.com>,
        Jude Onyenegecha <jude.onyenegecha@...ive.com>,
        Ben Dooks <ben.dooks@...ive.com>
Subject: [PATCH] bpf: fix check against plain integer v 'NULL'

When checking with sparse, btf_show_type_value() is causing a
warning about checking integer vs NULL when the macro is passed
a pointer, due to the 'value != 0' check. Stop sparse complaining
about any type-casting by adding a cast to the typeof(value).

This fixes the following sparse warnings:

kernel/bpf/btf.c:2579:17: warning: Using plain integer as NULL pointer
kernel/bpf/btf.c:2581:17: warning: Using plain integer as NULL pointer
kernel/bpf/btf.c:3407:17: warning: Using plain integer as NULL pointer
kernel/bpf/btf.c:3758:9: warning: Using plain integer as NULL pointer

Signed-off-by: Ben Dooks <ben.dooks@...ive.com>
---
 kernel/bpf/btf.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index eb12d4f705cc..9a6e5f71bbd2 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -1108,7 +1108,8 @@ __printf(2, 3) static void btf_show(struct btf_show *show, const char *fmt, ...)
  */
 #define btf_show_type_value(show, fmt, value)				       \
 	do {								       \
-		if ((value) != 0 || (show->flags & BTF_SHOW_ZERO) ||	       \
+		if ((value) != (__typeof__(value))0 ||			       \
+		    (show->flags & BTF_SHOW_ZERO) ||			       \
 		    show->state.depth == 0) {				       \
 			btf_show(show, "%s%s" fmt "%s%s",		       \
 				 btf_show_indent(show),			       \
-- 
2.35.1