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 <[email protected]>
---
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$d; \n\
- return (const void *)\"\\ \n\
- "
- , file_sz, obj_name);
+ static const char data[] __attribute__((__aligned__(8))) = \"\\\n\
+ ",
+ obj_name
+ );
/* embed contents of BPF object file */
print_hex(obj_data, file_sz);
@@ -1231,6 +1231,9 @@ static int do_skeleton(int argc, char **argv)
codegen("\
\n\
\"; \n\
+ \n\
+ *sz = sizeof(data) - 1; \n\
+ return (const void *)data; \n\
} \n\
\n\
#ifdef __cplusplus \n\
--
2.42.0.582.g8ccd20d70d-goog
On 03/10/2023 05:29, Ian Rogers wrote:
> On Mon, Oct 2, 2023 at 3:32 PM Ian Rogers <[email protected]> wrote:
>>
>> libbpf accesses the ELF data requiring at least 8 byte alignment,
>> however, the data is generated into a C string that doesn't guarantee
>> alignment. Fix this by assigning to an aligned char array, use sizeof
>> on the array, less one for the \0 terminator.
>>
>> Signed-off-by: Ian Rogers <[email protected]>
this looks like a great catch to me!
Reviewed-by: Alan Maguire <[email protected]>
>> ---
>
> Perhaps this could have a fixes tag:
> Fixes: d510296d331a ("bpftool: Use syscall/loader program in "prog
> load" and "gen skeleton" command.")
>
Yep, or perhaps
Fixes: a6cc6b34b93e ("bpftool: Provide a helper method for accessing
skeleton's embedded ELF data")
> The unaligned problem was seen in perf's offcpu code as well as bcc's
> libbpf_tools. I didn't see problems with map data and opts data, but
> inspection of the code shows they likely have the same issue. I was
> testing with -fsanitize=alignment and
> -fsanitize-undefined-trap-on-error.
>
> Thanks,
> Ian
>
>> tools/bpf/bpftool/gen.c | 15 +++++++++------
>> 1 file changed, 9 insertions(+), 6 deletions(-)
>>
>> diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
>> index 2883660d6b67..b8ebcee9bc56 100644
>> --- a/tools/bpf/bpftool/gen.c
>> +++ b/tools/bpf/bpftool/gen.c
>> @@ -1209,7 +1209,7 @@ static int do_skeleton(int argc, char **argv)
>> codegen("\
>> \n\
>> \n\
>> - s->data = (void *)%2$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
>>
>