netdev - [PATCH bpf-next 3/3] libbpf: Use string table index from index table if needed

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Message-Id: <20210121202203.9346-4-jolsa@kernel.org>
Date:   Thu, 21 Jan 2021 21:22:03 +0100
From:   Jiri Olsa <jolsa@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>
Cc:     dwarves@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Yonghong Song <yhs@...com>,
        Hao Luo <haoluo@...gle.com>, Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Mark Wielaard <mjw@...hat.com>
Subject: [PATCH bpf-next 3/3] libbpf: Use string table index from index table if needed

For very large ELF objects (with many sections), we could
get special value SHN_XINDEX (65535) for elf object's string
table index - e_shstrndx.

Call elf_getshdrstrndx to get the proper string table index,
instead of reading it directly from ELF header.

Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
 tools/lib/bpf/btf.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index 9970a288dda5..d9c10830d749 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -858,6 +858,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
 	Elf_Scn *scn = NULL;
 	Elf *elf = NULL;
 	GElf_Ehdr ehdr;
+	size_t shstrndx;
 
 	if (elf_version(EV_CURRENT) == EV_NONE) {
 		pr_warn("failed to init libelf for %s\n", path);
@@ -882,7 +883,14 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
 		pr_warn("failed to get EHDR from %s\n", path);
 		goto done;
 	}
-	if (!elf_rawdata(elf_getscn(elf, ehdr.e_shstrndx), NULL)) {
+
+	if (elf_getshdrstrndx(elf, &shstrndx)) {
+		pr_warn("failed to get section names section index for %s\n",
+			path);
+		goto done;
+	}
+
+	if (!elf_rawdata(elf_getscn(elf, shstrndx), NULL)) {
 		pr_warn("failed to get e_shstrndx from %s\n", path);
 		goto done;
 	}
@@ -897,7 +905,7 @@ static struct btf *btf_parse_elf(const char *path, struct btf *base_btf,
 				idx, path);
 			goto done;
 		}
-		name = elf_strptr(elf, ehdr.e_shstrndx, sh.sh_name);
+		name = elf_strptr(elf, shstrndx, sh.sh_name);
 		if (!name) {
 			pr_warn("failed to get section(%d) name from %s\n",
 				idx, path);
-- 
2.27.0