netdev - [PATCH v2 bpf-next] tools/lib/bpf: fix -Wdiscarded-qualifiers under C23

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Message-ID: <fa4ec6c228a314a9f0995f80225a4c0e4d8ac2c9.1764341791.git.mikhail.v.gavrilov@gmail.com>
Date: Fri, 28 Nov 2025 19:59:45 +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,
	Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>
Subject: [PATCH v2 bpf-next] 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 the default hardening flags
of Fedora Rawhide, Arch Linux, openSUSE Tumbleweed, Gentoo, etc.

In C23, strstr() and strchr() return "const char *" in most cases,
making previous implicit casts invalid.

This breaks the build of tools/bpf/resolve_btfids on pristine
upstream kernel when using GCC 15 + glibc 2.42+.

Fix the three remaining instances with explicit casts.

No functional changes.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=2417601
Suggested-by: Florian Weimer <fweimer@...hat.com>
Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>

---
v2:
- Declare `res` as `const char *` — never modified.
- Keep `sym_sfx` as `char *` and cast — it is advanced in the loop.
- Cast `next_path` — declared as `char *` earlier in the function.
  Changing it to const would require refactoring the whole function,
  which is not justified for a tools/ file.
---
 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 dd3b2f57082d..22ccd50e9978 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8245,7 +8245,7 @@ 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)
@@ -11576,7 +11576,7 @@ 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
@@ -12164,7 +12164,7 @@ static int resolve_full_path(const char *file, char *result, size_t result_sz)
 
 			if (s[0] == ':')
 				s++;
-			next_path = strchr(s, ':');
+			next_path = (char *)strchr(s, ':');   /* declared as char * above */
 			seg_len = next_path ? next_path - s : strlen(s);
 			if (!seg_len)
 				continue;
-- 
2.52.0