[PATCH v6 1/2] bpftool: Align output skeleton ELF code

[PATCH v6 1/2] bpftool: Align output skeleton ELF code

[Ian Rogers]

libbpf accesses the ELF data requiring at least 8 byte alignment,
however, the data is generated into a C string that doesn't guarantee
alignment. Fix this by assigning to an aligned char array. Use sizeof
on the array, less one for the \0 terminator, rather than generating a
constant.

Fixes: a6cc6b34b93e ("bpftool: Provide a helper method for accessing skeleton's embedded ELF data")
Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Quentin Monnet <quentin@isovalent.com>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
---
 tools/bpf/bpftool/gen.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 04c47745b3ea..882bf8e6e70e 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -1209,7 +1209,7 @@ static int do_skeleton(int argc, char **argv)
 	codegen("\
 		\n\
 									    \n\
-			s->data = %2$s__elf_bytes(&s->data_sz);		    \n\
+			s->data = %1$s__elf_bytes(&s->data_sz);		    \n\
 									    \n\
 			obj->skeleton = s;				    \n\
 			return 0;					    \n\
@@ -1218,12 +1218,12 @@ static int do_skeleton(int argc, char **argv)
 			return err;					    \n\
 		}							    \n\
 									    \n\
-		static inline const void *%2$s__elf_bytes(size_t *sz)	    \n\
+		static inline const void *%1$s__elf_bytes(size_t *sz)	    \n\
 		{							    \n\
-			*sz = %1$d;					    \n\
-			return (const void *)\"\\			    \n\
-		"
-		, file_sz, obj_name);
+			static const char data[] __attribute__((__aligned__(8))) = \"\\\n\
+		",
+		obj_name
+	);
 
 	/* embed contents of BPF object file */
 	print_hex(obj_data, file_sz);
@@ -1231,6 +1231,9 @@ static int do_skeleton(int argc, char **argv)
 	codegen("\
 		\n\
 		\";							    \n\
+									    \n\
+			*sz = sizeof(data) - 1;				    \n\
+			return (const void *)data;			    \n\
 		}							    \n\
 									    \n\
 		#ifdef __cplusplus					    \n\
-- 
2.42.0.609.gbb76f46606-goog

[PATCH v6 2/2] bpftool: Align bpf_load_and_run_opts insns and data

[Ian Rogers]

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@google.com>
Acked-by: Quentin Monnet <quentin@isovalent.com>
---
 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 882bf8e6e70e..ee3ce2b8000d 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;
 
-- 
2.42.0.609.gbb76f46606-goog

Re: [PATCH v6 1/2] bpftool: Align output skeleton ELF code

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <andrii@kernel.org>:

On Fri,  6 Oct 2023 21:44:38 -0700 you wrote:
> libbpf accesses the ELF data requiring at least 8 byte alignment,
> however, the data is generated into a C string that doesn't guarantee
> alignment. Fix this by assigning to an aligned char array. Use sizeof
> on the array, less one for the \0 terminator, rather than generating a
> constant.
> 
> Fixes: a6cc6b34b93e ("bpftool: Provide a helper method for accessing skeleton's embedded ELF data")
> Signed-off-by: Ian Rogers <irogers@google.com>
> Acked-by: Quentin Monnet <quentin@isovalent.com>
> Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
> 
> [...]

Here is the summary with links:
  - [v6,1/2] bpftool: Align output skeleton ELF code
    https://git.kernel.org/bpf/bpf-next/c/23671f4dfd10
  - [v6,2/2] bpftool: Align bpf_load_and_run_opts insns and data
    https://git.kernel.org/bpf/bpf-next/c/1be84ca53ca0

You are awesome, thank you!
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