From 3d2cf6c5bd35b0d72716b47bdd7e3892388aafc4 Mon Sep 17 00:00:00 2001
From: PiRK <pierrekn@gmail.com>
Date: Fri, 29 Jan 2021 11:49:51 +0100
Subject: [PATCH 1/2] initialize variable in tests

This was detected while running the tests with the `-Wconditional-uninitialized` flag

```
./autogen.sh
CC=clang CFLAGS="-Wconditional-uninitialized" ./configure
make check
```

The resulting warning is a false positive, but setting the value to -1
ensures that the CHECK below will fail if recid is never written to.
---
 src/tests.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/tests.c b/src/tests.c
index c2d5e28924..4110bb9a70 100644
--- a/src/tests.c
+++ b/src/tests.c
@@ -4324,8 +4324,10 @@ void test_ecdsa_sign_verify(void) {
     secp256k1_scalar one;
     secp256k1_scalar msg, key;
     secp256k1_scalar sigr, sigs;
-    int recid;
     int getrec;
+    /* Initialize recid to suppress a false positive -Wconditional-uninitialized in clang.
+       VG_UNDEF ensures that valgrind will still treat the variable as uninitialized. */
+    int recid = -1; VG_UNDEF(&recid, sizeof(recid));
     random_scalar_order_test(&msg);
     random_scalar_order_test(&key);
     secp256k1_ecmult_gen(&ctx->ecmult_gen_ctx, &pubj, &key);

From 99a1cfec1740a914aa416a87fd0acbde5426b969 Mon Sep 17 00:00:00 2001
From: PiRK <pierrekn@gmail.com>
Date: Sun, 31 Jan 2021 18:41:35 +0100
Subject: [PATCH 2/2] print warnings for conditional-uninitialized

This compiler flag is available for clang but not gcc.

Test plan:

```
autogen.sh
./configure
make check
CC=clang ./configure
make check
```

If a variable is used uninitialized, the warning should look something
like:
```
  CC       src/tests-tests.o
src/tests.c:4336:15: warning: variable 'recid' may be uninitialized when used here [-Wconditional-uninitialized]
        CHECK(recid >= 0 && recid < 4);
              ^~~~~
./src/util.h:54:18: note: expanded from macro 'CHECK'
    if (EXPECT(!(cond), 0)) { \
                 ^~~~
./src/util.h:41:39: note: expanded from macro 'EXPECT'
                                      ^
src/tests.c:4327:14: note: initialize the variable 'recid' to silence this warning
    int recid;
             ^
              = 0
1 warning generated.
```
---
 configure.ac | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/configure.ac b/configure.ac
index 451915ccfd..d9a7ddb6a3 100644
--- a/configure.ac
+++ b/configure.ac
@@ -79,6 +79,15 @@ AC_COMPILE_IFELSE([AC_LANG_SOURCE([[char foo;]])],
       CFLAGS="$saved_CFLAGS"
     ])
 
+saved_CFLAGS="$CFLAGS"
+CFLAGS="-Wconditional-uninitialized $CFLAGS"
+AC_MSG_CHECKING([if ${CC} supports -Wconditional-uninitialized])
+AC_COMPILE_IFELSE([AC_LANG_SOURCE([[char foo;]])],
+    [ AC_MSG_RESULT([yes]) ],
+    [ AC_MSG_RESULT([no])
+      CFLAGS="$saved_CFLAGS"
+    ])
+
 saved_CFLAGS="$CFLAGS"
 CFLAGS="-fvisibility=hidden $CFLAGS"
 AC_MSG_CHECKING([if ${CC} supports -fvisibility=hidden])