On Wed, Jan 29, 2014 at 03:51:50PM +0000, Valentin Bartenev wrote:
> details: http://hg.nginx.org/nginx/rev/01e2a5bcdd8f
> branches:
> changeset: 5545:01e2a5bcdd8f
> user: Piotr Sikora <piotr@cloudflare.com>
> date: Tue Jan 28 15:33:49 2014 -0800
> description:
> SSL: support ALPN (IETF's successor to NPN).
>
> Signed-off-by: Piotr Sikora <piotr@cloudflare.com>
This change breaks compilation with clang on systems
where OpenSSL doesn't have ALPN support:
: cc -c -pipe -O -Wall -Wextra -Wpointer-arith -Wconditional-uninitialized -Wno-unused-parameter -Werror -g -I src/core -I src/event -I src/event/modules -I src/os/unix -I /opt/local/include -I objs -I src/http -I src/http/modules \
: -o objs/src/http/ngx_http_request.o \
: src/http/ngx_http_request.c
: src/http/ngx_http_request.c:728:44: error: variable 'data' may be uninitialized when used here [-Werror,-Wconditional-uninitialized]
: if (len == spdy.len && ngx_strncmp(data, spdy.data, spdy.len) == 0) {
: ^~~~
: src/core/ngx_string.h:53:56: note: expanded from macro 'ngx_strncmp'
: #define ngx_strncmp(s1, s2, n) strncmp((const char *) s1, (const char *) s2, n)
: ^
: src/http/ngx_http_request.c:713:38: note: initialize the variable 'data' to silence this warning
: const unsigned char *data;
: ^
: = NULL
: 1 error generated.
: make[1]: *** [objs/src/http/ngx_http_request.o] Error 1
: make: *** [build] Error 2
clang(1) mistakenly thinks that "len" can be non-zero, and under
this condition "data" may be uninitialized.
It's possible to rewrite the code such as that it doesn't trigger
the warning:
diff --git a/src/http/ngx_http_request.c b/src/http/ngx_http_request.c
--- a/src/http/ngx_http_request.c
+++ b/src/http/ngx_http_request.c
@@ -713,11 +713,8 @@ ngx_http_ssl_handshake_handler(ngx_conne
const unsigned char *data;
static const ngx_str_t spdy = ngx_string(NGX_SPDY_NPN_NEGOTIATED);
- len = 0;
-
#ifdef TLSEXT_TYPE_application_layer_protocol_negotiation
SSL_get0_alpn_selected(c->ssl->connection, &data, &len);
-#endif
#ifdef TLSEXT_TYPE_next_proto_neg
if (len == 0) {
@@ -725,6 +722,10 @@ ngx_http_ssl_handshake_handler(ngx_conne
}
#endif
+#else /* TLSEXT_TYPE_next_proto_neg */
+ SSL_get0_next_proto_negotiated(c->ssl->connection, &data, &len);
+#endif
+
if (len == spdy.len && ngx_strncmp(data, spdy.data, spdy.len) == 0) {
ngx_http_spdy_init(c->read);
return;
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