linux-stable.git/tools/lib/bpf/libbpf.c, branch linux-4.3.y

bpf tools: New API to get name from a BPF object

2015-08-31T19:53:15+00:00

Before this patch there's no way to connect a loaded bpf object
to its source file. However, during applying perf's '--filter' to BPF
object, without this connection makes things harder, because perf loads
all programs together, but '--filter' setting is for each object.

The API of bpf_object__open_buffer() is changed to allow passing a name.
Fortunately, at this time there's only one user of it (perf test LLVM),
so we change it together.

Signed-off-by: Wang Nan 
Cc: Alexei Starovoitov 
Cc: Brendan Gregg 
Cc: Daniel Borkmann 
Cc: David Ahern 
Cc: He Kuang 
Cc: Jiri Olsa 
Cc: Kaixu Xia 
Cc: Masami Hiramatsu 
Cc: Namhyung Kim 
Cc: Peter Zijlstra 
Cc: Zefan Li 
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1440742821-44548-2-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo

bpf tools: Link all bpf objects onto a list

2015-08-07T13:16:59+00:00

To allow enumeration of all bpf_objects, keep them in a list (hidden to
caller). bpf_object__for_each_safe() is introduced to do this iteration.
It is safe even user close the object during iteration.

Signed-off-by: Wang Nan 
Acked-by: Alexei Starovoitov 
Cc: Brendan Gregg 
Cc: Daniel Borkmann 
Cc: David Ahern 
Cc: He Kuang 
Cc: Jiri Olsa 
Cc: Kaixu Xia 
Cc: Masami Hiramatsu 
Cc: Namhyung Kim 
Cc: Peter Zijlstra 
Cc: Zefan Li 
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1435716878-189507-23-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo

bpf tools: Introduce accessors for struct bpf_program

2015-08-07T13:16:59+00:00

This patch introduces accessors for user of libbpf to retrieve section
name and fd of a opened/loaded eBPF program. 'struct bpf_prog_handler'
is used for that purpose. Accessors of programs section name and file
descriptor are provided. Set/get private data are also impelmented.

Signed-off-by: Wang Nan 
Acked-by: Alexei Starovoitov 
Cc: Brendan Gregg 
Cc: Daniel Borkmann 
Cc: David Ahern 
Cc: He Kuang 
Cc: Jiri Olsa 
Cc: Kaixu Xia 
Cc: Masami Hiramatsu 
Cc: Namhyung Kim 
Cc: Peter Zijlstra 
Cc: Zefan Li 
Link: http://lkml.kernel.org/r/1435716878-189507-21-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo

bpf tools: Load eBPF programs in object files into kernel

2015-08-07T13:16:59+00:00

This patch utilizes previous introduced bpf_load_program to load
programs in the ELF file into kernel. Result is stored in 'fd' field in
'struct bpf_program'.

During loading, it allocs a log buffer and free it before return.  Note
that that buffer is not passed to bpf_load_program() if the first
loading try is successful. Doesn't use a statically allocated log buffer
to avoid potention multi-thread problem.

Instructions collected during opening is cleared after loading.

load_program() is created for loading a 'struct bpf_insn' array into
kernel, bpf_program__load() calls it. By this design we have a function
loads instructions into kernel. It will be used by further patches,
which creates different instances from a program and load them into
kernel.

Signed-off-by: Wang Nan 
Acked-by: Alexei Starovoitov 
Cc: Brendan Gregg 
Cc: Daniel Borkmann 
Cc: David Ahern 
Cc: He Kuang 
Cc: Jiri Olsa 
Cc: Kaixu Xia 
Cc: Masami Hiramatsu 
Cc: Namhyung Kim 
Cc: Peter Zijlstra 
Cc: Zefan Li 
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1435716878-189507-20-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo

bpf tools: Relocate eBPF programs

2015-08-07T13:16:58+00:00

If an eBPF program accesses a map, LLVM generates a load instruction
which loads an absolute address into a register, like this:

  ld_64   r1, 
  ...
  call    2

That ld_64 instruction will be recorded in relocation section.
To enable the usage of that map, relocation must be done by replacing
the immediate value by real map file descriptor so it can be found by
eBPF map functions.

This patch to the relocation work based on information collected by
patches:

'bpf tools: Collect symbol table from SHT_SYMTAB section',
'bpf tools: Collect relocation sections from SHT_REL sections'
and
'bpf tools: Record map accessing instructions for each program'.

For each instruction which needs relocation, it inject corresponding
file descriptor to imm field. As a part of protocol, src_reg is set to
BPF_PSEUDO_MAP_FD to notify kernel this is a map loading instruction.

This is the final part of map relocation patch. The principle of map
relocation is described in commit message of 'bpf tools: Collect symbol
table from SHT_SYMTAB section'.

Signed-off-by: Wang Nan 
Acked-by: Alexei Starovoitov 
Cc: Brendan Gregg 
Cc: Daniel Borkmann 
Cc: David Ahern 
Cc: He Kuang 
Cc: Jiri Olsa 
Cc: Kaixu Xia 
Cc: Masami Hiramatsu 
Cc: Namhyung Kim 
Cc: Peter Zijlstra 
Cc: Zefan Li 
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1435716878-189507-18-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo

bpf tools: Create eBPF maps defined in an object file

2015-08-07T13:16:58+00:00

This patch creates maps based on 'map' section in object file using
bpf_create_map(), and stores the fds into an array in 'struct
bpf_object'.

Previous patches parse ELF object file and collects required data, but
doesn't play with the kernel. They belong to the 'opening' phase. This
patch is the first patch in 'loading' phase. The 'loaded' field is
introduced in 'struct bpf_object' to avoid loading an object twice,
because the loading phase clears resources collected during the opening
which becomes useless after loading. In this patch, maps_buf is cleared.

Signed-off-by: Wang Nan 
Acked-by: Alexei Starovoitov 
Cc: Brendan Gregg 
Cc: Daniel Borkmann 
Cc: David Ahern 
Cc: He Kuang 
Cc: Jiri Olsa 
Cc: Kaixu Xia 
Cc: Masami Hiramatsu 
Cc: Namhyung Kim 
Cc: Peter Zijlstra 
Cc: Zefan Li 
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1435716878-189507-17-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo

bpf tools: Record map accessing instructions for each program

2015-08-07T13:16:58+00:00

This patch records the indices of instructions which are needed to be
relocated. That information is saved in the 'reloc_desc' field in
'struct bpf_program'. In the loading phase (this patch takes effect in
the 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 the 'opening' phase, the ELF information will no longer be valid in
the 'loading' phase. We have to locate the instructions before maps are
loaded, instead of directly modifying the instruction.

'struct bpf_map_def' is introduced in this patch to let us know how many
maps are defined in the object.

This is the third part of map relocation. The principle of map relocation
is described in commit message of 'bpf tools: Collect symbol table from
SHT_SYMTAB section'.

Signed-off-by: Wang Nan 
Acked-by: Alexei Starovoitov 
Cc: Brendan Gregg 
Cc: Daniel Borkmann 
Cc: David Ahern 
Cc: He Kuang 
Cc: Jiri Olsa 
Cc: Kaixu Xia 
Cc: Masami Hiramatsu 
Cc: Namhyung Kim 
Cc: Peter Zijlstra 
Cc: Zefan Li 
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1435716878-189507-15-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo

bpf tools: Collect relocation sections from SHT_REL sections

2015-08-07T13:16:57+00:00

This patch collects relocation sections into 'struct object'.  Such
sections are used for connecting maps to bpf programs. 'reloc' field in
'struct bpf_object' is introduced for storing such information.

This patch simply store the data into 'reloc' field. Following patch
will parse them to know the exact instructions which are needed to be
relocated.

Note that the collected data will be invalid after ELF object file is
closed.

This is the second patch related to map relocation. The first one is
'bpf tools: Collect symbol table from SHT_SYMTAB section'. The
principle of map relocation is described in its commit message.

Signed-off-by: Wang Nan 
Acked-by: Alexei Starovoitov 
Cc: Brendan Gregg 
Cc: Daniel Borkmann 
Cc: David Ahern 
Cc: He Kuang 
Cc: Jiri Olsa 
Cc: Kaixu Xia 
Cc: Masami Hiramatsu 
Cc: Namhyung Kim 
Cc: Peter Zijlstra 
Cc: Zefan Li 
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1435716878-189507-14-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo

bpf tools: Collect eBPF programs from their own sections

2015-08-07T13:16:57+00:00

This patch collects all programs in an object file into an array of
'struct bpf_program' for further processing. That structure is for
representing each eBPF program. 'bpf_prog' should be a better name, but
it has been used by linux/filter.h. Although it is a kernel space name,
I still prefer to call it 'bpf_program' to prevent possible confusion.

bpf_object__add_program() creates a new 'struct bpf_program' object.
It first init a variable in stack using bpf_program__init(), then if
success, enlarges obj->programs array and copy the new object in.

Signed-off-by: Wang Nan 
Acked-by: Alexei Starovoitov 
Cc: Brendan Gregg 
Cc: Daniel Borkmann 
Cc: David Ahern 
Cc: He Kuang 
Cc: Jiri Olsa 
Cc: Kaixu Xia 
Cc: Masami Hiramatsu 
Cc: Namhyung Kim 
Cc: Peter Zijlstra 
Cc: Zefan Li 
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1435716878-189507-13-git-send-email-wangnan0@huawei.com
[ Made bpf_object__add_program() propagate the error (-EINVAL or -ENOMEM) ]
Signed-off-by: Arnaldo Carvalho de Melo

bpf tools: Collect symbol table from SHT_SYMTAB section

2015-08-07T13:16:57+00:00

This patch collects symbols section. This section is useful when linking
BPF maps.

What 'bpf_map_xxx()' functions actually require are map's file
descriptors (and the internal verifier converts fds into pointers to
'struct bpf_map'), which we don't know when compiling. Therefore, we
should make compiler generate a 'ldr_64 r1, ' instruction, and
fill the 'imm' field with the actual file descriptor when loading in
libbpf.

BPF programs should be written in this way:

 struct bpf_map_def SEC("maps") my_map = {
    .type = BPF_MAP_TYPE_HASH,
    .key_size = sizeof(unsigned long),
    .value_size = sizeof(unsigned long),
    .max_entries = 1000000,
 };

 SEC("my_func=sys_write")
 int my_func(void *ctx)
 {
     ...
     bpf_map_update_elem(&my_map, &key, &value, BPF_ANY);
     ...
 }

Compiler should convert '&my_map' into a 'ldr_64, r1, '
instruction, where imm should be the address of 'my_map'. According to
the address, libbpf knows which map it actually referenced, and then
fills the imm field with the 'fd' of that map created by it.

However, since we never really 'link' the object file, the imm field is
only a record in relocation section. Therefore libbpf should do the
relocation:

 1. In relocation section (type == SHT_REL), positions of each such
    'ldr_64' instruction are recorded with a reference of an entry in
    symbol table (SHT_SYMTAB);

 2. From records in symbol table we can find the indics of map
    variables.

Libbpf first record SHT_SYMTAB and positions of each instruction which
required bu such operation. Then create file descriptor. Finally, after
map creation complete, replace the imm field.

This is the first patch of BPF map related stuff. It records SHT_SYMTAB
into object's efile field for further use.

Signed-off-by: Wang Nan 
Acked-by: Alexei Starovoitov 
Cc: Brendan Gregg 
Cc: Daniel Borkmann 
Cc: David Ahern 
Cc: He Kuang 
Cc: Jiri Olsa 
Cc: Kaixu Xia 
Cc: Masami Hiramatsu 
Cc: Namhyung Kim 
Cc: Peter Zijlstra 
Cc: Zefan Li 
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1435716878-189507-12-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo