clang-21 compilation warning: implicit conversion loses integer precision

[xuganyu96]

Description

When compiling liboqs using clang-21, the compiler reported warning: implicit conversion loses integer precision: 'int' to 'unsigned char' [-Wimplicit-int-conversion]. This warning is present with both AppleClang 21 and Clang 21 installed from Homebrew. This warning is not present with Clang 18 installed from Homebrew.

$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:200:62: warning: implicit conversion loses integer precision: 'int' to 'unsigned char' [-Wimplicit-int-conversion]
  200 |                         ((unsigned char *)state)[lanePosition * 8 + offset + i] = ~data[i];
      |                                                                                 ~ ^~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:384:3: warning: implicit conversion loses integer precision: 'int' to 'unsigned char' [-Wimplicit-int-conversion]
  384 |                 COMPL(1);
      |                 ^~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:382:70: note: expanded from macro 'COMPL'
  382 | #define COMPL(lane) for(unsigned int i=0; i<8; i++) data[8*lane+i] = ~data[8*lane+i]
      |                                                                    ~ ^~~~~~~~~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:386:4: warning: implicit conversion loses integer precision: 'int' to 'unsigned char' [-Wimplicit-int-conversion]
  386 |                         COMPL(2);
      |                         ^~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:382:70: note: expanded from macro 'COMPL'
  382 | #define COMPL(lane) for(unsigned int i=0; i<8; i++) data[8*lane+i] = ~data[8*lane+i]
      |                                                                    ~ ^~~~~~~~~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:388:5: warning: implicit conversion loses integer precision: 'int' to 'unsigned char' [-Wimplicit-int-conversion]
  388 |                                 COMPL(8);
      |                                 ^~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:382:70: note: expanded from macro 'COMPL'
  382 | #define COMPL(lane) for(unsigned int i=0; i<8; i++) data[8*lane+i] = ~data[8*lane+i]
      |                                                                    ~ ^~~~~~~~~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:390:6: warning: implicit conversion loses integer precision: 'int' to 'unsigned char' [-Wimplicit-int-conversion]
  390 |                                         COMPL(12);
      |                                         ^~~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:382:70: note: expanded from macro 'COMPL'
  382 | #define COMPL(lane) for(unsigned int i=0; i<8; i++) data[8*lane+i] = ~data[8*lane+i]
      |                                                                    ~ ^~~~~~~~~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:392:7: warning: implicit conversion loses integer precision: 'int' to 'unsigned char' [-Wimplicit-int-conversion]
  392 |                                                 COMPL(17);
      |                                                 ^~~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:382:70: note: expanded from macro 'COMPL'
  382 | #define COMPL(lane) for(unsigned int i=0; i<8; i++) data[8*lane+i] = ~data[8*lane+i]
      |                                                                    ~ ^~~~~~~~~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:394:8: warning: implicit conversion loses integer precision: 'int' to 'unsigned char' [-Wimplicit-int-conversion]
  394 |                                                         COMPL(20);
      |                                                         ^~~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:382:70: note: expanded from macro 'COMPL'
  382 | #define COMPL(lane) for(unsigned int i=0; i<8; i++) data[8*lane+i] = ~data[8*lane+i]
      |                                                                    ~ ^~~~~~~~~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:459:3: warning: implicit conversion loses integer precision: 'int' to 'unsigned char' [-Wimplicit-int-conversion]
  459 |                 COMPL(1);
      |                 ^~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:457:59: note: expanded from macro 'COMPL'
  457 | #define COMPL(lane) for(i=0; i<8; i++) output[8*lane+i] = ~output[8*lane+i]
      |                                                         ~ ^~~~~~~~~~~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:461:4: warning: implicit conversion loses integer precision: 'int' to 'unsigned char' [-Wimplicit-int-conversion]
  461 |                         COMPL(2);
      |                         ^~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:457:59: note: expanded from macro 'COMPL'
  457 | #define COMPL(lane) for(i=0; i<8; i++) output[8*lane+i] = ~output[8*lane+i]
      |                                                         ~ ^~~~~~~~~~~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:463:5: warning: implicit conversion loses integer precision: 'int' to 'unsigned char' [-Wimplicit-int-conversion]
  463 |                                 COMPL(8);
      |                                 ^~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:457:59: note: expanded from macro 'COMPL'
  457 | #define COMPL(lane) for(i=0; i<8; i++) output[8*lane+i] = ~output[8*lane+i]
      |                                                         ~ ^~~~~~~~~~~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:465:6: warning: implicit conversion loses integer precision: 'int' to 'unsigned char' [-Wimplicit-int-conversion]
  465 |                                         COMPL(12);
      |                                         ^~~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:457:59: note: expanded from macro 'COMPL'
  457 | #define COMPL(lane) for(i=0; i<8; i++) output[8*lane+i] = ~output[8*lane+i]
      |                                                         ~ ^~~~~~~~~~~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:467:7: warning: implicit conversion loses integer precision: 'int' to 'unsigned char' [-Wimplicit-int-conversion]
  467 |                                                 COMPL(17);
      |                                                 ^~~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:457:59: note: expanded from macro 'COMPL'
  457 | #define COMPL(lane) for(i=0; i<8; i++) output[8*lane+i] = ~output[8*lane+i]
      |                                                         ~ ^~~~~~~~~~~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:469:8: warning: implicit conversion loses integer precision: 'int' to 'unsigned char' [-Wimplicit-int-conversion]
  469 |                                                         COMPL(20);
      |                                                         ^~~~~~~~~
$LIBOQS_DIR/src/common/sha3/xkcp_low/KeccakP-1600/plain-64bits/KeccakP-1600-opt64.c:457:59: note: expanded from macro 'COMPL'
  457 | #define COMPL(lane) for(i=0; i<8; i++) output[8*lane+i] = ~output[8*lane+i]
      |                                                         ~ ^~~~~~~~~~~~~~~~~
13 warnings generated.

Expected behaviour

There should not be any warnings.

liboqs version

ab0e07c

Environment

• Architecture: Apple Silicon
• OS: MacOS 26.4
• OpenSSL version: OpenSSL 3.6.1 27 Jan 2026 (Library: OpenSSL 3.6.1 27 Jan 2026)
• Compiler version used: Apple clang version 21.0.0 (clang-2100.0.123.102) and Homebrew clang version 21.1.8

Build command:

cmake -GNinja \
    -DCMAKE_C_COMPILER="/opt/homebrew/Cellar/llvm@21/21.1.8/bin/clang-21" \
    -DOQS_MINIMAL_BUILD="KEM_frodokem_640_aes" \
    -DCMAKE_OSX_DEPLOYMENT_TARGET="26.0" \
    -DOPENSSL_ROOT_DIR="/opt/homebrew/Cellar/openssl@3/3.6.1" \
    .. && ninja

Use of generative AI

No response

Additional information

No response

[xuganyu96]

Update: I also got ranlib: warning: xxx has no symbols when building with cmake -GNinja ..:

ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(verify.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(polyvec_basemul_acc_montgomery_cached_asm_k3.S.o)' has no symbols
ranlib: warning: 'liboqs.a(polyvec_basemul_acc_montgomery_cached_asm_k4.S.o)' has no symbols
ranlib: warning: 'liboqs.a(verify.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(verify.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(polyvec_basemul_acc_montgomery_cached_asm_k2.S.o)' has no symbols
ranlib: warning: 'liboqs.a(polyvec_basemul_acc_montgomery_cached_asm_k4.S.o)' has no symbols
ranlib: warning: 'liboqs.a(verify.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(verify.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(polyvec_basemul_acc_montgomery_cached_asm_k2.S.o)' has no symbols
ranlib: warning: 'liboqs.a(polyvec_basemul_acc_montgomery_cached_asm_k3.S.o)' has no symbols
ranlib: warning: 'liboqs.a(verify.c.o)' has no symbols
ranlib: warning: 'liboqs.a(ct.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(ct.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(ct.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(ct.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(ct.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(ct.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(params.c.o)' has no symbols
ranlib: warning: 'liboqs.a(params.c.o)' has no symbols
ranlib: warning: 'liboqs.a(params.c.o)' has no symbols
ranlib: warning: 'liboqs.a(params.c.o)' has no symbols
ranlib: warning: 'liboqs.a(params.c.o)' has no symbols
ranlib: warning: 'liboqs.a(params.c.o)' has no symbols
ranlib: warning: 'liboqs.a(params.c.o)' has no symbols
ranlib: warning: 'liboqs.a(params.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(verify.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(polyvec_basemul_acc_montgomery_cached_asm_k3.S.o)' has no symbols
ranlib: warning: 'liboqs.a(polyvec_basemul_acc_montgomery_cached_asm_k4.S.o)' has no symbols
ranlib: warning: 'liboqs.a(verify.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(verify.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(polyvec_basemul_acc_montgomery_cached_asm_k2.S.o)' has no symbols
ranlib: warning: 'liboqs.a(polyvec_basemul_acc_montgomery_cached_asm_k4.S.o)' has no symbols
ranlib: warning: 'liboqs.a(verify.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(verify.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(polyvec_basemul_acc_montgomery_cached_asm_k2.S.o)' has no symbols
ranlib: warning: 'liboqs.a(polyvec_basemul_acc_montgomery_cached_asm_k3.S.o)' has no symbols
ranlib: warning: 'liboqs.a(verify.c.o)' has no symbols
ranlib: warning: 'liboqs.a(ct.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(ct.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(ct.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(ct.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(ct.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(ct.c.o)' has no symbols
ranlib: warning: 'liboqs.a(debug.c.o)' has no symbols
ranlib: warning: 'liboqs.a(params.c.o)' has no symbols
ranlib: warning: 'liboqs.a(params.c.o)' has no symbols
ranlib: warning: 'liboqs.a(params.c.o)' has no symbols
ranlib: warning: 'liboqs.a(params.c.o)' has no symbols
ranlib: warning: 'liboqs.a(params.c.o)' has no symbols
ranlib: warning: 'liboqs.a(params.c.o)' has no symbols
ranlib: warning: 'liboqs.a(params.c.o)' has no symbols
ranlib: warning: 'liboqs.a(params.c.o)' has no symbols