linux-kernel - [RFC PATCH v10 13/50] bpf tools: Collect relocation sections from SHT

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Message-ID: <1435716878-189507-14-git-send-email-wangnan0@huawei.com>
Date:	Wed, 1 Jul 2015 02:14:01 +0000
From:	Wang Nan <wangnan0@...wei.com>
To:	<acme@...nel.org>, <ast@...mgrid.com>, <brendan.d.gregg@...il.com>,
	<daniel@...earbox.net>, <namhyung@...nel.org>,
	<masami.hiramatsu.pt@...achi.com>, <paulus@...ba.org>,
	<a.p.zijlstra@...llo.nl>, <mingo@...hat.com>, <jolsa@...nel.org>,
	<dsahern@...il.com>
CC:	<linux-kernel@...r.kernel.org>, <lizefan@...wei.com>,
	<hekuang@...wei.com>, <xiakaixu@...wei.com>, <pi3orama@....com>
Subject: [RFC PATCH v10 13/50] 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.

Signed-off-by: Wang Nan <wangnan0@...wei.com>
Acked-by: Alexei Starovoitov <ast@...mgrid.com>
---
 tools/lib/bpf/libbpf.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 9c01b55f..f3ace51 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -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[];
 };
@@ -220,6 +225,9 @@ 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;
@@ -440,6 +448,24 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
 			} else
 				pr_debug("found program %s\n",
 					 prog->section_name);
+		} 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;
-- 
1.8.3.4

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