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


    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@huawei.com>
    > ...
    >> +/*
    >> + * 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
    ‘bpf_map_def’ [-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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