Merge branch 'bpf-libbpf-relo-fix-and-tests'

Jesper Dangaard Brouer says:

====================
While playing with using libbpf for the Suricata project, we had
issues LLVM >= 4.0.1 generating ELF files that could not be loaded
with libbpf (tools/lib/bpf/).

During the troubleshooting phase, I wrote a test program and improved
the debugging output in libbpf.  I turned this into a selftests
program, and it also serves as a code example for libbpf in itself.

I discovered that there are at least three ELF load issues with
libbpf.  I left them as TODO comments in (tools/testing/selftests/bpf)
test_libbpf.sh. I've only fixed the load issue with eh_frames, and
other types of relo-section that does not have exec flags.  We can
work on the other issues later.
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

5 files changed, 253 insertions, 16 deletions

diff --git a/tools/include/uapi/linux/bpf_common.h b/tools/include/uapi/linux/bpf_common.h
index 18be90725ab0..ee97668bdadb 100644
--- a/tools/include/uapi/linux/bpf_common.h
+++ b/tools/include/uapi/linux/bpf_common.h
@@ -15,9 +15,10 @@
 
 /* ld/ldx fields */
 #define BPF_SIZE(code)  ((code) & 0x18)
-#define         BPF_W           0x00
-#define         BPF_H           0x08
-#define         BPF_B           0x10
+#define         BPF_W           0x00 /* 32-bit */
+#define         BPF_H           0x08 /* 16-bit */
+#define         BPF_B           0x10 /*  8-bit */
+/* eBPF         BPF_DW          0x18    64-bit */
 #define BPF_MODE(code)  ((code) & 0xe0)
 #define         BPF_IMM         0x00
 #define         BPF_ABS         0x20
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index c64840365433..97073d649c1a 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -319,8 +319,8 @@ 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;
         }
 
@@ -742,6 +742,24 @@ bpf_object__init_maps(struct bpf_object *obj)
         return 0;
 }
 
+static bool section_have_execinstr(struct bpf_object *obj, int idx)
+{
+        Elf_Scn *scn;
+        GElf_Shdr sh;
+
+        scn = elf_getscn(obj->efile.elf, idx);
+        if (!scn)
+                return false;
+
+        if (gelf_getshdr(scn, &sh) != &sh)
+                return false;
+
+        if (sh.sh_flags & SHF_EXECINSTR)
+                return true;
+
+        return false;
+}
+
 static int bpf_object__elf_collect(struct bpf_object *obj)
 {
         Elf *elf = obj->efile.elf;
@@ -763,29 +781,29 @@ 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);
 
@@ -825,6 +843,14 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
                 } else if (sh.sh_type == SHT_REL) {
                         void *reloc = obj->efile.reloc;
                         int nr_reloc = obj->efile.nr_reloc + 1;
+                        int sec = sh.sh_info; /* points to other section */
+
+                        /* Only do relo for section with exec instructions */
+                        if (!section_have_execinstr(obj, sec)) {
+                                pr_debug("skip relo %s(%d) for section(%d)\n",
+                                         name, idx, sec);
+                                continue;
+                        }
 
                         reloc = realloc(reloc,
                                         sizeof(*obj->efile.reloc) * nr_reloc);
@@ -840,6 +866,8 @@ 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;
@@ -1119,8 +1147,7 @@ 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;
                 }
 
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 566d6adc172a..5c43c187f27c 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -13,6 +13,7 @@ endif
 CFLAGS += -Wall -O2 -I$(APIDIR) -I$(LIBDIR) -I$(GENDIR) $(GENFLAGS) -I../../../include
 LDLIBS += -lcap -lelf -lrt -lpthread
 
+# Order correspond to 'make run_tests' order
 TEST_GEN_PROGS = test_verifier test_tag test_maps test_lru_map test_lpm_map test_progs \
         test_align test_verifier_log test_dev_cgroup test_tcpbpf_user
 
@@ -22,15 +23,24 @@ TEST_GEN_FILES = test_pkt_access.o test_xdp.o test_l4lb.o test_tcp_estats.o test
         test_l4lb_noinline.o test_xdp_noinline.o test_stacktrace_map.o \
         sample_map_ret0.o test_tcpbpf_kern.o
 
-TEST_PROGS := test_kmod.sh test_xdp_redirect.sh test_xdp_meta.sh \
+# Order correspond to 'make run_tests' order
+TEST_PROGS := test_kmod.sh \
+        test_libbpf.sh \
+        test_xdp_redirect.sh \
+        test_xdp_meta.sh \
         test_offload.py
 
+# Compile but not part of 'make run_tests'
+TEST_GEN_PROGS_EXTENDED = test_libbpf_open
+
 include ../lib.mk
 
 BPFOBJ := $(OUTPUT)/libbpf.a cgroup_helpers.c
 
 $(TEST_GEN_PROGS): $(BPFOBJ)
 
+$(TEST_GEN_PROGS_EXTENDED): $(OUTPUT)/libbpf.a
+
 .PHONY: force
 
 # force a rebuild of BPFOBJ when its dependencies are updated
diff --git a/tools/testing/selftests/bpf/test_libbpf.sh b/tools/testing/selftests/bpf/test_libbpf.sh
new file mode 100755
index 000000000000..d97dc914cd49
--- /dev/null
+++ b/tools/testing/selftests/bpf/test_libbpf.sh
@@ -0,0 +1,49 @@
+#!/bin/sh