[FFmpeg-devel] [PATCH] avformat/ffrtmpcrypt: Fix int-conversion warning

[Frank Plowman]

The gcrypt definition of `bn_new` used to use `AVERROR`, however it is
called in `dh_generate_key` and `ff_dh_init` which return pointers. As a
result, compiling with gcrypt and the ffrtmpcrypt protocol resulted in an
int-conversion warning. GCC 14 may upgrade these to errors [1].

This patch fixes the problem by changing the macro to remove `AVERROR`
and instead set `bn` to null if the allocation fails. This is the
behaviour of all the other `bn_new` implementations and so the result is
already checked at all the callsites. AFAICT, this should be the only
change needed to get ffmpeg off Fedora's naughty list of projects with
warnings which may be upgraded to errors in GCC 14 [2].

[1]: https://gcc.gnu.org/pipermail/gcc/2023-May/241264.html
[2]: https://www.mail-archive.com/devel@lists.fedoraproject.org/msg196024.html

Signed-off-by: Frank Plowman <post at frankplowman.com>
---
 libavformat/rtmpdh.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/libavformat/rtmpdh.c b/libavformat/rtmpdh.c
index 5ddae537a1..6a6c2ccd87 100644
--- a/libavformat/rtmpdh.c
+++ b/libavformat/rtmpdh.c
@@ -113,15 +113,18 @@ static int bn_modexp(FFBigNum bn, FFBigNum y, FFBigNum q, FFBigNum p)
     return 0;
 }
 #elif CONFIG_GCRYPT
-#define bn_new(bn)                                              \
-    do {                                                        \
-        if (!gcry_control(GCRYCTL_INITIALIZATION_FINISHED_P)) { \
-            if (!gcry_check_version("1.5.4"))                   \
-                return AVERROR(EINVAL);                         \
-            gcry_control(GCRYCTL_DISABLE_SECMEM, 0);            \
-            gcry_control(GCRYCTL_INITIALIZATION_FINISHED, 0);   \
-        }                                                       \
-        bn = gcry_mpi_new(1);                                   \
+#define bn_new(bn)                                                \
+    do {                                                          \
+        if (!gcry_control(GCRYCTL_INITIALIZATION_FINISHED_P)) {   \
+            if (gcry_check_version("1.5.4")) {                    \
+                gcry_control(GCRYCTL_DISABLE_SECMEM, 0);          \
+                gcry_control(GCRYCTL_INITIALIZATION_FINISHED, 0); \
+            }                                                     \
+        }                                                         \
+        if (gcry_control(GCRYCTL_INITIALIZATION_FINISHED_P))      \
+            bn = gcry_mpi_new(1);                                 \
+        else                                                      \
+            bn = NULL;                                            \
     } while (0)
 #define bn_free(bn)                 gcry_mpi_release(bn)
 #define bn_set_word(bn, w)          gcry_mpi_set_ui(bn, w)
-- 
2.43.0