[PATCH] bpftool: Fix error prompt of strerror

[Tianyi Liu <i.pear@xxxxxxxxxxx>]

strerror() excepts a posivite errno, however libbpf_get_error()
or variable err will never be positive when an error occurs.
This causes bpftool to output too many "unknown error", even a simple
"file not exist" error can't get an accurate prompt.
This patch fixed all "strerror(err)" patten in bpftool.

Signed-off-by: Tianyi Liu <i.pear@xxxxxxxxxxx>
---
 tools/bpf/bpftool/btf.c           | 6 +++---
 tools/bpf/bpftool/gen.c           | 4 ++--
 tools/bpf/bpftool/map_perf_ring.c | 4 ++--
 3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c
index 0744bd115..ac586c0e5 100644
--- a/tools/bpf/bpftool/btf.c
+++ b/tools/bpf/bpftool/btf.c
@@ -643,7 +643,7 @@ static int do_dump(int argc, char **argv)
 		if (err) {
 			btf = NULL;
 			p_err("failed to load BTF from %s: %s",
-			      *argv, strerror(err));
+			      *argv, strerror(errno));
 			goto done;
 		}
 		NEXT_ARG();
@@ -689,7 +689,7 @@ static int do_dump(int argc, char **argv)
 		btf = btf__load_from_kernel_by_id_split(btf_id, base_btf);
 		err = libbpf_get_error(btf);
 		if (err) {
-			p_err("get btf by id (%u): %s", btf_id, strerror(err));
+			p_err("get btf by id (%u): %s", btf_id, strerror(errno));
 			goto done;
 		}
 	}
@@ -825,7 +825,7 @@ build_btf_type_table(struct hashmap *tab, enum bpf_obj_type type,
 				      u32_as_hash_field(id));
 		if (err) {
 			p_err("failed to append entry to hashmap for BTF ID %u, object ID %u: %s",
-			      btf_id, id, strerror(errno));
+			      btf_id, id, strerror(-err));
 			goto err_free;
 		}
 	}
diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 7070dcffa..0783069f6 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -1594,14 +1594,14 @@ static int do_object(int argc, char **argv)
 
 		err = bpf_linker__add_file(linker, file, NULL);
 		if (err) {
-			p_err("failed to link '%s': %s (%d)", file, strerror(err), err);
+			p_err("failed to link '%s': %s (%d)", file, strerror(errno), err);
 			goto out;
 		}
 	}
 
 	err = bpf_linker__finalize(linker);
 	if (err) {
-		p_err("failed to finalize ELF file: %s (%d)", strerror(err), err);
+		p_err("failed to finalize ELF file: %s (%d)", strerror(errno), err);
 		goto out;
 	}
 
diff --git a/tools/bpf/bpftool/map_perf_ring.c b/tools/bpf/bpftool/map_perf_ring.c
index 6b0c41015..1650b7127 100644
--- a/tools/bpf/bpftool/map_perf_ring.c
+++ b/tools/bpf/bpftool/map_perf_ring.c
@@ -198,7 +198,7 @@ int do_event_pipe(int argc, char **argv)
 	err = libbpf_get_error(pb);
 	if (err) {
 		p_err("failed to create perf buffer: %s (%d)",
-		      strerror(err), err);
+		      strerror(errno), err);
 		goto err_close_map;
 	}
 
@@ -213,7 +213,7 @@ int do_event_pipe(int argc, char **argv)
 		err = perf_buffer__poll(pb, 200);
 		if (err < 0 && err != -EINTR) {
 			p_err("perf buffer polling failed: %s (%d)",
-			      strerror(err), err);
+			      strerror(errno), err);
 			goto err_close_pb;
 		}
 	}
-- 
2.37.3