On Mon, Oct 2, 2023 at 3:32 PM Ian Rogers <irogers@xxxxxxxxxx> 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.
>
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> ---
Perhaps this could have a fixes tag:
Fixes: d510296d331a ("bpftool: Use syscall/loader program in "prog
load" and "gen skeleton" command.")
The unaligned problem was seen in perf's offcpu code as well as bcc's
libbpf_tools. I didn't see problems with map data and opts data, but
inspection of the code shows they likely have the same issue. I was
testing with -fsanitize=alignment and
-fsanitize-undefined-trap-on-error.
Thanks,
Ian
> 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 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\
> --
> 2.42.0.582.g8ccd20d70d-goog
>
