`-Wmaybe-uninitialized` when compiling with `-O1`

hebasto commented at 11:29 am on June 27, 2023: member

 0$ ./autogen.sh && ./configure CFLAGS=-O1
 1$ make clean > /dev/null && make > /dev/null 
 2In file included from src/secp256k1.c:30:
 3In function 'secp256k1_ecmult_strauss_wnaf',
 4    inlined from 'secp256k1_ecmult' at src/ecmult_impl.h:353:5:
 5src/ecmult_impl.h:291:5: warning: 'aux' may be used uninitialized [-Wmaybe-uninitialized]
 6  291 |     secp256k1_ge_table_set_globalz(ECMULT_TABLE_SIZE(WINDOW_A) * no, state->pre_a, state->aux);
 7      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 8In file included from src/secp256k1.c:29:
 9src/group_impl.h: In function 'secp256k1_ecmult':
10src/group_impl.h:224:13: note: by argument 3 of type 'const secp256k1_fe *' to 'secp256k1_ge_table_set_globalz' declared here
11  224 | static void secp256k1_ge_table_set_globalz(size_t len, secp256k1_ge *a, const secp256k1_fe *zr) {
12      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
13src/ecmult_impl.h:345:18: note: 'aux' declared here
14  345 |     secp256k1_fe aux[ECMULT_TABLE_SIZE(WINDOW_A)];
15      |                  ^~~
16In file included from src/secp256k1.c:30,
17                 from src/bench_internal.c:8:
18In function ‘secp256k1_ecmult_strauss_wnaf’,
19    inlined from ‘secp256k1_ecmult’ at src/ecmult_impl.h:353:5:
20src/ecmult_impl.h:291:5: warning: ‘aux’ may be used uninitialized [-Wmaybe-uninitialized]
21  291 |     secp256k1_ge_table_set_globalz(ECMULT_TABLE_SIZE(WINDOW_A) * no, state->pre_a, state->aux);
22      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
23In file included from src/secp256k1.c:29:
24src/group_impl.h: In function ‘secp256k1_ecmult’:
25src/group_impl.h:224:13: note: by argument 3 of type ‘const secp256k1_fe *’ to ‘secp256k1_ge_table_set_globalz’ declared here
26  224 | static void secp256k1_ge_table_set_globalz(size_t len, secp256k1_ge *a, const secp256k1_fe *zr) {
27      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
28src/ecmult_impl.h:345:18: note: ‘aux’ declared here
29  345 |     secp256k1_fe aux[ECMULT_TABLE_SIZE(WINDOW_A)];
30      |                  ^~~

Using gcc 12.2.

No warnings with clang 15.

real-or-random commented at 12:52 pm on June 27, 2023: contributor

Wrapping the call in if (no > 0) suppresses this:

0    if (no > 0) {
1        secp256k1_ge_table_set_globalz(ECMULT_TABLE_SIZE(WINDOW_A) * no, state->pre_a, state->aux);
2    }

(Or adding SECP256K1_INLINE to secp256k1_ge_table_set_globalz, but this seems a bit arbitrary…)

hebasto commented at 1:10 pm on June 27, 2023: member

Wrapping the call in if (no > 0) suppresses this:

0    if (no > 0) {
1        secp256k1_ge_table_set_globalz(ECMULT_TABLE_SIZE(WINDOW_A) * no, state->pre_a, state->aux);
2    }

Would if (no) be more consistent with the code in for loop above?

real-or-random commented at 2:27 pm on June 27, 2023: contributor

Would if (no) be more consistent with the code in for loop above?

I think so.

hebasto cross-referenced this on Jun 28, 2023 from issue Avoid `-Wmaybe-uninitialized` when compiling with `gcc -O1` by hebasto

real-or-random closed this on Jul 3, 2023

-Wmaybe-uninitialized when compiling with -O1 #1361

`-Wmaybe-uninitialized` when compiling with `-O1` #1361