netdev - [PATCH v3] tools/lib/bpf: fix -Wdiscarded-qualifiers under C23

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Message-ID: <20251206080556.685835-1-mikhail.v.gavrilov@gmail.com>
Date: Sat,  6 Dec 2025 13:05:56 +0500
From: Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>
To: bpf@...r.kernel.org
Cc: andrii@...nel.org,
	ast@...nel.org,
	daniel@...earbox.net,
	netdev@...r.kernel.org,
	fweimer@...hat.com,
	andrii.nakryiko@...il.com,
	Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>
Subject: [PATCH v3] tools/lib/bpf: fix -Wdiscarded-qualifiers under C23

glibc ≥ 2.42 (GCC 15) defaults to -std=gnu23, which promotes
-Wdiscarded-qualifiers to an error.

In C23, strstr() and strchr() return "const char *".

Declare `res` and `next_path` as const char * — they are never modified.
Keep `sym_sfx` as char * because it is advanced in a loop.

Suggested-by: Florian Weimer <fweimer@...hat.com>
Suggested-by: Andrii Nakryiko <andrii.nakryiko@...il.com>
Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>
---
v2: use const char * where possible (Florian, Andrii)
v3: declare res/next_path as const char * (never modified)
    keep cast for sym_sfx (advanced in loop)
---
 tools/lib/bpf/libbpf.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 3dc8a8078815..81782471f1d0 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8484,7 +8484,7 @@ static int kallsyms_cb(unsigned long long sym_addr, char sym_type,
 	struct bpf_object *obj = ctx;
 	const struct btf_type *t;
 	struct extern_desc *ext;
-	char *res;
+	const char *res;
 
 	res = strstr(sym_name, ".llvm.");
 	if (sym_type == 'd' && res)
@@ -11820,7 +11820,7 @@ static int avail_kallsyms_cb(unsigned long long sym_addr, char sym_type,
 		 */
 		char sym_trim[256], *psym_trim = sym_trim, *sym_sfx;
 
-		if (!(sym_sfx = strstr(sym_name, ".llvm.")))
+		if (!(sym_sfx = (char *)strstr(sym_name, ".llvm.")))  /* needs mutation */
 			return 0;
 
 		/* psym_trim vs sym_trim dance is done to avoid pointer vs array
@@ -12401,7 +12401,7 @@ static int resolve_full_path(const char *file, char *result, size_t result_sz)
 		if (!search_paths[i])
 			continue;
 		for (s = search_paths[i]; s != NULL; s = strchr(s, ':')) {
-			char *next_path;
+			const char *next_path;
 			int seg_len;
 
 			if (s[0] == ':')
-- 
2.52.0