netdev - [PATCH bpf-next 4/8] tools: libbpf: restore the ability to load programs from .text section

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Date:   Thu, 28 Jun 2018 14:41:38 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     alexei.starovoitov@...il.com, daniel@...earbox.net
Cc:     oss-drivers@...ronome.com, netdev@...r.kernel.org,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
Subject: [PATCH bpf-next 4/8] tools: libbpf: restore the ability to load programs from .text section

libbpf used to be able to load programs from the default section
called '.text'.  It's not very common to leave sections unnamed,
but if it happens libbpf will fail to load the programs reporting
-EINVAL from the kernel.  The -EINVAL comes from bpf_obj_name_cpy()
because since 48cca7e44f9f ("libbpf: add support for bpf_call")
libbpf does not resolve program names for programs in '.text',
defaulting to '.text'.  '.text', however, does not pass the
(isalnum(*src) || *src == '_') check in bpf_obj_name_cpy().

With few extra lines of code we can limit the pseudo call
assumptions only to objects which actually contain code relocations.

Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@...ronome.com>
---
 tools/lib/bpf/libbpf.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 7bc02d93e277..e2401b95f08d 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -234,6 +234,7 @@ struct bpf_object {
 	size_t nr_maps;
 
 	bool loaded;
+	bool has_pseudo_calls;
 
 	/*
 	 * Information when doing elf related work. Only valid if fd
@@ -400,10 +401,6 @@ bpf_object__init_prog_names(struct bpf_object *obj)
 		const char *name = NULL;
 
 		prog = &obj->programs[pi];
-		if (prog->idx == obj->efile.text_shndx) {
-			name = ".text";
-			goto skip_search;
-		}
 
 		for (si = 0; si < symbols->d_size / sizeof(GElf_Sym) && !name;
 		     si++) {
@@ -426,12 +423,15 @@ bpf_object__init_prog_names(struct bpf_object *obj)
 			}
 		}
 
+		if (!name && prog->idx == obj->efile.text_shndx)
+			name = ".text";
+
 		if (!name) {
 			pr_warning("failed to find sym for prog %s\n",
 				   prog->section_name);
 			return -EINVAL;
 		}
-skip_search:
+
 		prog->name = strdup(name);
 		if (!prog->name) {
 			pr_warning("failed to allocate memory for prog sym %s\n",
@@ -981,6 +981,7 @@ bpf_program__collect_reloc(struct bpf_program *prog, GElf_Shdr *shdr,
 			prog->reloc_desc[i].type = RELO_CALL;
 			prog->reloc_desc[i].insn_idx = insn_idx;
 			prog->reloc_desc[i].text_off = sym.st_value;
+			obj->has_pseudo_calls = true;
 			continue;
 		}
 
@@ -1426,6 +1427,12 @@ bpf_program__load(struct bpf_program *prog,
 	return err;
 }
 
+static bool bpf_program__is_function_storage(struct bpf_program *prog,
+					     struct bpf_object *obj)
+{
+	return prog->idx == obj->efile.text_shndx && obj->has_pseudo_calls;
+}
+
 static int
 bpf_object__load_progs(struct bpf_object *obj)
 {
@@ -1433,7 +1440,7 @@ bpf_object__load_progs(struct bpf_object *obj)
 	int err;
 
 	for (i = 0; i < obj->nr_programs; i++) {
-		if (obj->programs[i].idx == obj->efile.text_shndx)
+		if (bpf_program__is_function_storage(&obj->programs[i], obj))
 			continue;
 		err = bpf_program__load(&obj->programs[i],
 					obj->license,
@@ -2247,7 +2254,7 @@ int bpf_prog_load_xattr(const struct bpf_prog_load_attr *attr,
 		bpf_program__set_expected_attach_type(prog,
 						      expected_attach_type);
 
-		if (prog->idx != obj->efile.text_shndx && !first_prog)
+		if (!bpf_program__is_function_storage(prog, obj) && !first_prog)
 			first_prog = prog;
 	}
 
-- 
2.17.1