[PATCH v2] libbpf: add pr_warn() for EINVAL cases in linker_sanity_check_elf

[Sergei Trofimovich <slyich@xxxxxxxxx>]

Before the change on `i686-linux` `systemd` build failed as:

    $ bpftool gen object src/core/bpf/socket_bind/socket-bind.bpf.o src/core/bpf/socket_bind/socket-bind.bpf.unstripped.o
    Error: failed to link 'src/core/bpf/socket_bind/socket-bind.bpf.unstripped.o': Invalid argument (22)

After the change it fails as:

    $ bpftool gen object src/core/bpf/socket_bind/socket-bind.bpf.o src/core/bpf/socket_bind/socket-bind.bpf.unstripped.o
    libbpf: ELF section #9 has inconsistent alignment addr=8 != d=4 in src/core/bpf/socket_bind/socket-bind.bpf.unstripped.o
    Error: failed to link 'src/core/bpf/socket_bind/socket-bind.bpf.unstripped.o': Invalid argument (22)

Now it's slightly easier to figure out what is wrong with an ELF file.

CC: Alexei Starovoitov <ast@xxxxxxxxxx>
CC: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
CC: Andrii Nakryiko <andrii@xxxxxxxxxx>
CC: Martin KaFai Lau <martin.lau@xxxxxxxxx>
CC: Song Liu <song@xxxxxxxxxx>
CC: Yonghong Song <yonghong.song@xxxxxxxxx>
CC: John Fastabend <john.fastabend@xxxxxxxxx>
CC: KP Singh <kpsingh@xxxxxxxxxx>
CC: Stanislav Fomichev <sdf@xxxxxxxxxx>
CC: Hao Luo <haoluo@xxxxxxxxxx>
CC: Jiri Olsa <jolsa@xxxxxxxxxx>
CC: Eduard Zingerman <eddyz87@xxxxxxxxx>
CC: bpf@xxxxxxxxxxxxxxx
Signed-off-by: Sergei Trofimovich <slyich@xxxxxxxxx>
---
 tools/lib/bpf/linker.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)
Change since v1:
Following Eduard's suggestion added one extra pr_warn() call around
section alignment and added compared values into warning messages.

diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index 5ced96d99f8c..52a2901e8bd0 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -719,13 +719,25 @@ static int linker_sanity_check_elf(struct src_obj *obj)
 			return -EINVAL;
 		}
 
-		if (sec->shdr->sh_addralign && !is_pow_of_2(sec->shdr->sh_addralign))
+		if (sec->shdr->sh_addralign && !is_pow_of_2(sec->shdr->sh_addralign)) {
+			pr_warn("ELF section #%zu alignment %llu is non pow-of-2 alignment in %s\n",
+				sec->sec_idx, (long long unsigned)sec->shdr->sh_addralign,
+				obj->filename);
 			return -EINVAL;
-		if (sec->shdr->sh_addralign != sec->data->d_align)
+		}
+		if (sec->shdr->sh_addralign != sec->data->d_align) {
+			pr_warn("ELF section #%zu has inconsistent alignment addr=%llu != d=%llu in %s\n",
+				sec->sec_idx, (long long unsigned)sec->shdr->sh_addralign,
+				(long long unsigned)sec->data->d_align, obj->filename);
 			return -EINVAL;
+		}
 
-		if (sec->shdr->sh_size != sec->data->d_size)
+		if (sec->shdr->sh_size != sec->data->d_size) {
+			pr_warn("ELF section #%zu has inconsistent section size sh=%llu != d=%llu in %s\n",
+				sec->sec_idx, (long long unsigned)sec->shdr->sh_size,
+				(long long unsigned)sec->data->d_size, obj->filename);
 			return -EINVAL;
+		}
 
 		switch (sec->shdr->sh_type) {
 		case SHT_SYMTAB:
@@ -737,8 +749,12 @@ static int linker_sanity_check_elf(struct src_obj *obj)
 			break;
 		case SHT_PROGBITS:
 			if (sec->shdr->sh_flags & SHF_EXECINSTR) {
-				if (sec->shdr->sh_size % sizeof(struct bpf_insn) != 0)
+				if (sec->shdr->sh_size % sizeof(struct bpf_insn) != 0) {
+					pr_warn("ELF section #%zu has unexpected size alignment %llu in %s\n",
+						sec->sec_idx, (long long unsigned)sec->shdr->sh_size,
+						obj->filename);
 					return -EINVAL;
+				}
 			}
 			break;
 		case SHT_NOBITS:
-- 
2.42.0