linux-kernel - [PATCH v2 2/2] bpftool: Align bpf_load_and_run

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Date:   Tue,  3 Oct 2023 12:14:12 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Quentin Monnet <quentin@...valent.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>,
        Yonghong Song <yonghong.song@...ux.dev>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Ian Rogers <irogers@...gle.com>
Subject: [PATCH v2 2/2] bpftool: Align bpf_load_and_run_opts insns and data

A C string lacks alignment so use aligned arrays to avoid potential
alignment problems. Switch to using sizeof (less 1 for the \0
terminator) rather than a hardcode size constant.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
I was unable to find a test case for this part of the codegen using
Linux perf and libbpf tools code bases.
---
 tools/bpf/bpftool/gen.c | 43 ++++++++++++++++++++++-------------------
 1 file changed, 23 insertions(+), 20 deletions(-)

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index b8ebcee9bc56..e9a59b254c66 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -708,17 +708,22 @@ static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *h
 
 		codegen("\
 		\n\
-			skel->%1$s = skel_prep_map_data((void *)\"\\	    \n\
-		", ident);
+			{						    \n\
+				static const char data[] __attribute__((aligned__(8))) = \"\\\n\
+		");
 		mmap_data = bpf_map__initial_value(map, &mmap_size);
 		print_hex(mmap_data, mmap_size);
 		codegen("\
 		\n\
-		\", %1$zd, %2$zd);					    \n\
-			if (!skel->%3$s)				    \n\
-				goto cleanup;				    \n\
-			skel->maps.%3$s.initial_value = (__u64) (long) skel->%3$s;\n\
-		", bpf_map_mmap_sz(map), mmap_size, ident);
+		\";							    \n\
+									    \n\
+				skel->%1$s = skel_prep_map_data((void *)data, %2$zd,\n\
+								sizeof(data) - 1);\n\
+				if (!skel->%1$s)			    \n\
+					goto cleanup;			    \n\
+				skel->maps.%1$s.initial_value = (__u64) (long) skel->%1$s;\n\
+			}						    \n \
+		", ident, bpf_map_mmap_sz(map));
 	}
 	codegen("\
 		\n\
@@ -733,32 +738,30 @@ static int gen_trace(struct bpf_object *obj, const char *obj_name, const char *h
 		{							    \n\
 			struct bpf_load_and_run_opts opts = {};		    \n\
 			int err;					    \n\
-									    \n\
-			opts.ctx = (struct bpf_loader_ctx *)skel;	    \n\
-			opts.data_sz = %2$d;				    \n\
-			opts.data = (void *)\"\\			    \n\
+			static const char opts_data[] __attribute__((aligned__(8))) = \"\\\n\
 		",
-		obj_name, opts.data_sz);
+		obj_name);
 	print_hex(opts.data, opts.data_sz);
 	codegen("\
 		\n\
 		\";							    \n\
+			static const char opts_insn[] __attribute__((aligned__(8))) = \"\\\n\
 		");
-
-	codegen("\
-		\n\
-			opts.insns_sz = %d;				    \n\
-			opts.insns = (void *)\"\\			    \n\
-		",
-		opts.insns_sz);
 	print_hex(opts.insns, opts.insns_sz);
 	codegen("\
 		\n\
 		\";							    \n\
+									    \n\
+			opts.ctx = (struct bpf_loader_ctx *)skel;	    \n\
+			opts.data_sz = sizeof(opts_data) - 1;		    \n\
+			opts.data = (void *)opts_data;			    \n\
+			opts.insns_sz = sizeof(opts_insn) - 1;		    \n\
+			opts.insns = (void *)opts_insn;			    \n\
+									    \n\
 			err = bpf_load_and_run(&opts);			    \n\
 			if (err < 0)					    \n\
 				return err;				    \n\
-		", obj_name);
+		");
 	bpf_object__for_each_map(map, obj) {
 		const char *mmap_flags;
 
-- 
2.42.0.582.g8ccd20d70d-goog