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[v3,1/2] bpftool: Align output skeleton ELF code

Message ID 20231004204334.3465116-1-irogers@google.com (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series [v3,1/2] bpftool: Align output skeleton ELF code | expand

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Commit Message

Ian Rogers Oct. 4, 2023, 8:43 p.m. UTC
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>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
---
 tools/bpf/bpftool/gen.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

Comments

Andrii Nakryiko Oct. 4, 2023, 9:56 p.m. UTC | #1
On Wed, Oct 4, 2023 at 1:43 PM Ian Rogers <irogers@google.com> 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>
> Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
> ---
>  tools/bpf/bpftool/gen.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
>

CI is not happy still, see [0]

  [0] https://github.com/kernel-patches/bpf/actions/runs/6411371996/job/17406696212

> diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> index 2883660d6b67..b8ebcee9bc56 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 = (void *)%2$s__elf_bytes(&s->data_sz);     \n\
> +                       s->data = (void *)%1$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
>
Ian Rogers Oct. 4, 2023, 10:21 p.m. UTC | #2
On Wed, Oct 4, 2023 at 2:56 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Wed, Oct 4, 2023 at 1:43 PM Ian Rogers <irogers@google.com> 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>
> > Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
> > ---
> >  tools/bpf/bpftool/gen.c | 15 +++++++++------
> >  1 file changed, 9 insertions(+), 6 deletions(-)
> >
>
> CI is not happy still, see [0]
>
>   [0] https://github.com/kernel-patches/bpf/actions/runs/6411371996/job/17406696212

Thanks, typo crept into patch 2/2. Will send v4.

Ian

> > diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> > index 2883660d6b67..b8ebcee9bc56 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 = (void *)%2$s__elf_bytes(&s->data_sz);     \n\
> > +                       s->data = (void *)%1$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
> >
diff mbox series

Patch

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 2883660d6b67..b8ebcee9bc56 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 = (void *)%2$s__elf_bytes(&s->data_sz);	    \n\
+			s->data = (void *)%1$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\