Commit b62f06e8 authored Jul 01, 2015 by Wang Nan Committed by Arnaldo Carvalho de Melo Aug 07, 2015

bpf tools: Collect relocation sections from SHT_REL sections



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 <wangnan0@huawei.com>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David Ahern <dsahern@gmail.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kaixu Xia <xiakaixu@huawei.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Zefan Li <lizefan@huawei.com>
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 <acme@redhat.com>

parent a5b8bd47

tools/lib/bpf/libbpf.c

+26 −0

Original line number	Diff line number	Diff line
		@@ -110,6 +110,11 @@ struct bpf_object {
		Elf *elf;
		GElf_Ehdr ehdr;
		Elf_Data *symbols;
		struct {
		GElf_Shdr shdr;
		Elf_Data *data;
		} *reloc;
		int nr_reloc;
		} efile;
		char path[];
		};
		@@ -231,6 +236,9 @@ static void bpf_object__elf_finish(struct bpf_object *obj)
		obj->efile.elf = NULL;
		}
		obj->efile.symbols = NULL;

		zfree(&obj->efile.reloc);
		obj->efile.nr_reloc = 0;
		zclose(obj->efile.fd);
		obj->efile.obj_buf = NULL;
		obj->efile.obj_buf_sz = 0;
		@@ -447,6 +455,24 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
		pr_warning("failed to alloc program %s (%s): %s",
		name, obj->path, errmsg);
		}
		} else if (sh.sh_type == SHT_REL) {
		void *reloc = obj->efile.reloc;
		int nr_reloc = obj->efile.nr_reloc + 1;

		reloc = realloc(reloc,
		sizeof(obj->efile.reloc) nr_reloc);
		if (!reloc) {
		pr_warning("realloc failed\n");
		err = -ENOMEM;
		} else {
		int n = nr_reloc - 1;

		obj->efile.reloc = reloc;
		obj->efile.nr_reloc = nr_reloc;

		obj->efile.reloc[n].shdr = sh;
		obj->efile.reloc[n].data = data;
		}
		}
		if (err)
		goto out;