Re: [RFC PATCH v3 18/37] bpf tools: Record map accessing instructions for each program

[Wangnan (F)]

On 2015/5/19 2:34, Alexei Starovoitov wrote:
> On 5/17/15 3:56 AM, Wang Nan wrote:
> > This patch records the indics of instructions which are needed to be
> > relocated. Those information are saved in 'reloc_desc' field in
> > 'struct bpf_program'. In loading phase (this patch takes effect in
> > opening phase), the collected instructions will be replaced by
> > map loading instructions.
> >
> > Since we are going to close the ELF file and clear all data at the end
> > of 'opening' phase, ELF information will no longer be valid in
> > 'loading' phase. We have to locate the instructions before maps are
> > loaded, instead of directly modifying the instruction.
> >
> > 'struct bpf_map_def' is introduce in this patch to let us know how many
> > maps defined in the object.
> >
> > Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
> ...
> > +/*
> > + * packed attribute is unnecessary for 'bpf_map_def'.
> > + */
> > +struct bpf_map_def {
> > +    unsigned int type;
> > +    unsigned int key_size;
> > +    unsigned int value_size;
> > +    unsigned int max_entries;
> > +};
>
> the comment looks out of place. 'packed' is necessary somewhere else?
> What were you concerned about here?

I see a warning message:

 make: Entering directory `/home/w00229757/kernel-hydrogen/tools/lib/bpf'
   CC       libbpf.o
 In file included from libbpf.c:23:0:
 libbpf.h:31:1: error: packed attribute is unnecessary for 
âbpf_map_defâ [-Werror=packed]
  } __attribute__((packed));
  ^
 cc1: all warnings being treated as errors

if I append __attribute__((packed)) here. This is because 
Makefile.include in tools/script
as '-Wpacked' warning message and it is inherited by perf. When 
compiling with perf this
problem breaks compiling. Therefore I don't use 'packed' here. However I 
think there should
be one. This comment is for that.










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