Is default -Wl,--no-undefined desired? #1556

1. 
   hebasto commented at 4:38 am on June 28, 2024: member

   Consider the following diff:

    0--- a/src/secp256k1.c
    1+++ b/src/secp256k1.c
    2@@ -765,7 +765,9 @@ int secp256k1_ec_pubkey_tweak_mul(const secp256k1_context* ctx, secp256k1_pubkey
    3     return ret;
    4 }
    5 
    6+void undefined_function(void);
    7 int secp256k1_context_randomize(secp256k1_context* ctx, const unsigned char *seed32) {
    8+    undefined_function();
    9     VERIFY_CHECK(ctx != NULL);
   10     ARG_CHECK(secp256k1_context_is_proper(ctx));
   11 
   

   It compiles fine:

   0$ ./autogen.sh
   1$ ./configure
   2$ make libsecp256k1.la
   

   However, it should fail like that:

    0$ ./autogen.sh
    1$ ./configure LDFLAGS="-Wl,--no-undefined"
    2$ make libsecp256k1.la
    3  CC       src/libsecp256k1_la-secp256k1.lo
    4  CC       src/libsecp256k1_precomputed_la-precomputed_ecmult.lo
    5  CC       src/libsecp256k1_precomputed_la-precomputed_ecmult_gen.lo
    6  CCLD     libsecp256k1_precomputed.la
    7  CCLD     libsecp256k1.la
    8/usr/bin/ld: src/.libs/libsecp256k1_la-secp256k1.o: in function `secp256k1_context_randomize':
    9/home/hebasto/git/secp256k1/secp256k1/src/secp256k1.c:770:(.text+0xee01): undefined reference to `undefined_function'
   10collect2: error: ld returned 1 exit status
   11make: *** [Makefile:1020: libsecp256k1.la] Error 1
   

2. real-or-random added the label build on Jun 28, 2024
3. 
   real-or-random commented at 9:18 am on June 28, 2024: contributor

   I think we want to check for undefined symbols, and -Wl,--no-undefined seems to be the canonical way of doing so.

   I assume one important exception is builds with external default callbacks, so we can’t enable it in these cases.

Contributors
hebasto real-or-random

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