[PATCH bpf-next v1 01/17] bpf: Add verifier diagnostics report helpers

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

Add a small diagnostics renderer for verifier reports and wire it into the
BPF build. The initial helpers emit the common text structure: a failure
header plus reusable report sections.

Wrap report prose at 120 columns so Reason and Suggestion text stays readable
without changing source or instruction gutters.

No verifier call sites use the helpers yet, so existing verifier output
is unchanged.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/Makefile      |   2 +-
 kernel/bpf/diagnostics.c | 110 +++++++++++++++++++++++++++++++++++++++
 kernel/bpf/diagnostics.h |  19 +++++++
 3 files changed, 130 insertions(+), 1 deletion(-)
 create mode 100644 kernel/bpf/diagnostics.c
 create mode 100644 kernel/bpf/diagnostics.h

diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index 4dc41bf5780c..90255d80e5be 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -6,7 +6,7 @@ cflags-nogcse-$(CONFIG_X86)$(CONFIG_CC_IS_GCC) := -fno-gcse
 endif
 CFLAGS_core.o += -Wno-override-init $(cflags-nogcse-yy)
 
-obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o cnum.o log.o token.o liveness.o const_fold.o
+obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o cnum.o log.o token.o liveness.o const_fold.o diagnostics.o
 obj-$(CONFIG_BPF_SYSCALL) += bpf_iter.o map_iter.o task_iter.o prog_iter.o link_iter.o
 obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o bloom_filter.o
 obj-$(CONFIG_BPF_SYSCALL) += local_storage.o queue_stack_maps.o ringbuf.o bpf_insn_array.o
diff --git a/kernel/bpf/diagnostics.c b/kernel/bpf/diagnostics.c
new file mode 100644
index 000000000000..a6684adc0c31
--- /dev/null
+++ b/kernel/bpf/diagnostics.c
@@ -0,0 +1,110 @@
+// SPDX-License-Identifier: GPL-2.0-only
+// Copyright (c) 2026 Meta Platforms, Inc. and affiliates.
+
+#include <linux/bpf_verifier.h>
+#include <linux/stdarg.h>
+#include <linux/string.h>
+
+#include "diagnostics.h"
+
+#define verbose(env, fmt, args...) bpf_verifier_log_write(env, fmt, ##args)
+#define BPF_DIAG_TEXT_WIDTH 120
+#define BPF_DIAG_TEXT_INDENT "  "
+#define BPF_DIAG_MSG_LEN 512
+
+static void bpf_diag_print_wrapped_prefixed(struct bpf_verifier_env *env,
+					    const char *first_prefix,
+					    const char *next_prefix,
+					    const char *text)
+{
+	const char *prefix = first_prefix;
+
+	while (*text) {
+		const char *line = text;
+		int prefix_len = strlen(prefix);
+		int text_width = BPF_DIAG_TEXT_WIDTH - prefix_len;
+		int len = 0, last_space = -1;
+
+		if (text_width < 1)
+			text_width = 1;
+
+		while (line[len] && line[len] != '\n' && len < text_width) {
+			if (line[len] == ' ')
+				last_space = len;
+			len++;
+		}
+
+		if (line[len] && line[len] != '\n' && last_space > 0)
+			len = last_space;
+
+		verbose(env, "%s%.*s\n", prefix, len, line);
+
+		text = line + len;
+		while (*text == ' ')
+			text++;
+		if (*text == '\n')
+			text++;
+
+		prefix = next_prefix;
+	}
+}
+
+static void bpf_diag_print_wrapped_text(struct bpf_verifier_env *env,
+					const char *text)
+{
+	bpf_diag_print_wrapped_prefixed(env, BPF_DIAG_TEXT_INDENT,
+					BPF_DIAG_TEXT_INDENT, text);
+}
+
+static void bpf_diag_vprint_indented(struct bpf_verifier_env *env,
+				     const char *fmt, va_list args)
+{
+	char buf[1024];
+
+	if (!bpf_verifier_log_needed(&env->log))
+		return;
+
+	vscnprintf(buf, sizeof(buf), fmt, args);
+	bpf_diag_print_wrapped_text(env, buf);
+}
+
+void bpf_diag_report_header(struct bpf_verifier_env *env,
+			    const char *category, const char *problem)
+{
+	char problem_buf[BPF_DIAG_MSG_LEN];
+
+	strscpy(problem_buf, problem ?: "", sizeof(problem_buf));
+	if (problem_buf[0] >= 'a' && problem_buf[0] <= 'z')
+		problem_buf[0] += 'A' - 'a';
+
+	verbose(env, "\nVerification failed: %s: %s\n", category,
+		problem_buf);
+}
+
+void bpf_diag_report_reason(struct bpf_verifier_env *env, const char *fmt, ...)
+{
+	va_list args;
+
+	bpf_diag_report_section(env, "Reason");
+
+	va_start(args, fmt);
+	bpf_diag_vprint_indented(env, fmt, args);
+	va_end(args);
+}
+
+void bpf_diag_report_section(struct bpf_verifier_env *env, const char *title)
+{
+	verbose(env, "\n%s:\n", title);
+}
+
+void bpf_diag_report_suggestion(struct bpf_verifier_env *env, const char *fmt, ...)
+{
+	va_list args;
+
+	bpf_diag_report_section(env, "Suggestion");
+
+	va_start(args, fmt);
+	bpf_diag_vprint_indented(env, fmt, args);
+	va_end(args);
+	verbose(env, "\n");
+}
diff --git a/kernel/bpf/diagnostics.h b/kernel/bpf/diagnostics.h
new file mode 100644
index 000000000000..f13a939722bf
--- /dev/null
+++ b/kernel/bpf/diagnostics.h
@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0-only
+// Copyright (c) 2026 Meta Platforms, Inc. and affiliates.
+
+#ifndef __BPF_DIAGNOSTICS_H
+#define __BPF_DIAGNOSTICS_H
+
+#include <linux/compiler_attributes.h>
+
+struct bpf_verifier_env;
+
+void bpf_diag_report_header(struct bpf_verifier_env *env,
+			    const char *category, const char *problem);
+void bpf_diag_report_reason(struct bpf_verifier_env *env, const char *fmt, ...)
+	__printf(2, 3);
+void bpf_diag_report_section(struct bpf_verifier_env *env, const char *title);
+void bpf_diag_report_suggestion(struct bpf_verifier_env *env, const char *fmt, ...)
+	__printf(2, 3);
+
+#endif /* __BPF_DIAGNOSTICS_H */
-- 
2.53.0