linux-kernel - [RFC PATCH v3 17/37] bpf tools: Collect relocation sections from SHT

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Message-ID: <1431860222-61636-18-git-send-email-wangnan0@huawei.com>
Date:	Sun, 17 May 2015 10:56:42 +0000
From:	Wang Nan <wangnan0@...wei.com>
To:	<paulus@...ba.org>, <a.p.zijlstra@...llo.nl>, <mingo@...hat.com>,
	<acme@...nel.org>, <namhyung@...nel.org>, <jolsa@...nel.org>,
	<dsahern@...il.com>, <ast@...mgrid.com>, <daniel@...earbox.net>,
	<brendan.d.gregg@...il.com>, <masami.hiramatsu.pt@...achi.com>
CC:	<lizefan@...wei.com>, <linux-kernel@...r.kernel.org>,
	<pi3orama@....com>
Subject: [RFC PATCH v3 17/37] 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 informations.

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>
---
 tools/lib/bpf/libbpf.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 18b221f..8fd29a9 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;
 	} elf;
 };
 #define obj_elf_valid(o)	((o)->elf.fd >= 0)
@@ -233,6 +238,12 @@ static void bpf_obj_clear_elf(struct bpf_object *obj)
 	}
 	obj->elf.symbols = NULL;
 
+	if (obj->elf.reloc) {
+		free(obj->elf.reloc);
+		obj->elf.reloc = NULL;
+		obj->elf.nr_reloc = 0;
+	}
+
 	if (obj->elf.fd >= 0) {
 		close(obj->elf.fd);
 		obj->elf.fd = -1;
@@ -484,6 +495,24 @@ static int bpf_obj_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->elf.reloc;
+			int nr_reloc = obj->elf.nr_reloc;
+
+			reloc = realloc(reloc,
+					sizeof(*obj->elf.reloc) * (++nr_reloc));
+			if (!reloc) {
+				pr_warning("realloc failed\n");
+				err = -ENOMEM;
+			} else {
+				int n = nr_reloc - 1;
+
+				obj->elf.reloc = reloc;
+				obj->elf.nr_reloc = nr_reloc;
+
+				obj->elf.reloc[n].shdr = sh;
+				obj->elf.reloc[n].data = data;
+			}
 		}
 		if (err)
 			goto out;
-- 
1.8.3.4

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