netdev - [PATCH v2 bpf-next 2/9] libbpf: preserve errno before calling into user callback

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Message-ID: <20190529173611.4012579-3-andriin@fb.com>
Date:   Wed, 29 May 2019 10:36:04 -0700
From:   Andrii Nakryiko <andriin@...com>
To:     <andrii.nakryiko@...il.com>, <netdev@...r.kernel.org>,
        <bpf@...r.kernel.org>, <ast@...com>, <daniel@...earbox.net>,
        <kernel-team@...com>
CC:     Andrii Nakryiko <andriin@...com>
Subject: [PATCH v2 bpf-next 2/9] libbpf: preserve errno before calling into user callback

pr_warning ultimately may call into user-provided callback function,
which can clobber errno value, so we need to save it before that.

Acked-by: Song Liu <songliubraving@...com>
Signed-off-by: Andrii Nakryiko <andriin@...com>
---
 tools/lib/bpf/libbpf.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index c6c9d632624a..5af331cb8e4f 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -565,12 +565,12 @@ static int bpf_object__elf_init(struct bpf_object *obj)
 	} else {
 		obj->efile.fd = open(obj->path, O_RDONLY);
 		if (obj->efile.fd < 0) {
-			char errmsg[STRERR_BUFSIZE];
-			char *cp = libbpf_strerror_r(errno, errmsg,
-						     sizeof(errmsg));
+			char errmsg[STRERR_BUFSIZE], *cp;
 
+			err = -errno;
+			cp = libbpf_strerror_r(err, errmsg, sizeof(errmsg));
 			pr_warning("failed to open %s: %s\n", obj->path, cp);
-			return -errno;
+			return err;
 		}
 
 		obj->efile.elf = elf_begin(obj->efile.fd,
-- 
2.17.1