netdev - [bpf-next V2 PATCH 2/5] tools/libbpf: improve the pr_debug statements to contain section numbers

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Message-ID: <151792885302.16520.13605739913635643189.stgit@firesoul>
Date:   Tue, 06 Feb 2018 15:54:13 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     netdev@...r.kernel.org, Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        wangnan0@...wei.com
Cc:     jakub.kicinski@...ronome.com, joe@....org, acme@...hat.com,
        eric@...it.org, Jesper Dangaard Brouer <brouer@...hat.com>,
        yhs@...com
Subject: [bpf-next V2 PATCH 2/5] tools/libbpf: improve the pr_debug
 statements to contain section numbers

While debugging a bpf ELF loading issue, I needed to correlate the
ELF section number with the failed relocation section reference.
Thus, add section numbers/index to the pr_debug.

In debug mode, also print section that were skipped.  This helped
me identify that a section (.eh_frame) was skipped, and this was
the reason the relocation section (.rel.eh_frame) could not find
that section number.

The section numbers corresponds to the readelf tools Section Headers [Nr].

Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
---
 tools/lib/bpf/libbpf.c |   25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 30c776375118..b4eeaa3ebff5 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -315,8 +315,8 @@ bpf_program__init(void *data, size_t size, char *section_name, int idx,
 
 	prog->section_name = strdup(section_name);
 	if (!prog->section_name) {
-		pr_warning("failed to alloc name for prog under section %s\n",
-			   section_name);
+		pr_warning("failed to alloc name for prog under section(%d) %s\n",
+			   idx, section_name);
 		goto errout;
 	}
 
@@ -759,29 +759,29 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
 
 		idx++;
 		if (gelf_getshdr(scn, &sh) != &sh) {
-			pr_warning("failed to get section header from %s\n",
-				   obj->path);
+			pr_warning("failed to get section(%d) header from %s\n",
+				   idx, obj->path);
 			err = -LIBBPF_ERRNO__FORMAT;
 			goto out;
 		}
 
 		name = elf_strptr(elf, ep->e_shstrndx, sh.sh_name);
 		if (!name) {
-			pr_warning("failed to get section name from %s\n",
-				   obj->path);
+			pr_warning("failed to get section(%d) name from %s\n",
+				   idx, obj->path);
 			err = -LIBBPF_ERRNO__FORMAT;
 			goto out;
 		}
 
 		data = elf_getdata(scn, 0);
 		if (!data) {
-			pr_warning("failed to get section data from %s(%s)\n",
-				   name, obj->path);
+			pr_warning("failed to get section(%d) data from %s(%s)\n",
+				   idx, name, obj->path);
 			err = -LIBBPF_ERRNO__FORMAT;
 			goto out;
 		}
-		pr_debug("section %s, size %ld, link %d, flags %lx, type=%d\n",
-			 name, (unsigned long)data->d_size,
+		pr_debug("section(%d) %s, size %ld, link %d, flags %lx, type=%d\n",
+			 idx, name, (unsigned long)data->d_size,
 			 (int)sh.sh_link, (unsigned long)sh.sh_flags,
 			 (int)sh.sh_type);
 
@@ -836,6 +836,8 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
 				obj->efile.reloc[n].shdr = sh;
 				obj->efile.reloc[n].data = data;
 			}
+		} else {
+			pr_debug("skip section(%d) %s\n", idx, name);
 		}
 		if (err)
 			goto out;
@@ -1115,8 +1117,7 @@ static int bpf_object__collect_reloc(struct bpf_object *obj)
 
 		prog = bpf_object__find_prog_by_idx(obj, idx);
 		if (!prog) {
-			pr_warning("relocation failed: no %d section\n",
-				   idx);
+			pr_warning("relocation failed: no section(%d)\n", idx);
 			return -LIBBPF_ERRNO__RELOC;
 		}