de4238f92f4c067f099663f68d9772105de81d75 build: consolidate reduced export checks (fanquake)
012bdec1b7df01906566a6526e56f27d57d1653b build: add building libconsensus to end-of-configure output (fanquake)
8f360e349e365870b40a6873917c81de714ae41a build: remove ax_gcc_func_attribute macro (fanquake)
f054a089ecfbdc4732e6f705a10e93189074f41c build: remove AX_GCC_FUNC_ATTRIBUTE test for dllimport (fanquake)
7cd0a696643a824ab6f6911278f116f01c5af662 build: test for __declspec(dllexport) in configure (fanquake)
1624e17b5430dfe808bb3b1b79dfa53bf45aa053 build: remove duplicate visibility attribute detection (fanquake)
Pull request description:
Darwin targets do not have a `protected` visibility function attribute, see [LLVM explanation](8e9a505139/clang/lib/Basic/Targets/OSTargets.h (L131)). This means that the `AX_GCC_FUNC_ATTRIBUTE` check for `visibility` fails:
```bash
configure:24513: checking for __attribute__((visibility))
configure:24537: g++ -std=c++11 -o conftest -g -O2 -DHAVE_BUILD_INFO -D__STDC_FORMAT_MACROS -DMAC_OSX -DOBJC_OLD_DISPATCH_PROTOTYPES=0 -Wl,-headerpad_max_install_names conftest.cpp >&5
conftest.cpp:35:56: warning: target does not support 'protected' visibility; using 'default' [-Wunsupported-visibility]
int foo_pro( void ) __attribute__((visibility("protected")));
^
1 warning generated.
configure:24537: $? = 0
configure:24550: result: no
```
This leads to `EXPORT_SYMBOL` being [defined to nothing](f4de89edfa/src/script/bitcoinconsensus.h (L29)), as `HAVE_FUNC_ATTRIBUTE_VISIBILITY` is not defined, and when building with reduced exports, you end up with a libbitcoinconsensus.dylib that doesn't export any `_bitcoinconsensus_*` symbols.
```bash
➜ git:(master) nm -C src/.libs/libbitcoinconsensus.dylib | rg _bitcoinconsensus_
➜ git:(master)
```
We do have a [second check](f4de89edfa/configure.ac (L882)) for the `visibility` attribute, which works for Darwin as it's only testing for default visibility, however the result of this check isn't used at all. It was added in #4725, along with the `--enable-reduce-exports` option, however when libbitcoinconsensus was added in #5235, it used the results of the added `AX_GCC_FUNC_ATTRIBUTE` calls.
This PR removes our usage of the AX_GCC_FUNC_ATTRIBUTE macro entirely, in favour of our own checks in configure. This meant adding a check for `dllexport`, which I've tested as working with both [GCC](https://gcc.gnu.org/onlinedocs/gcc/Microsoft-Windows-Function-Attributes.html) and [Clang](https://releases.llvm.org/10.0.0/tools/clang/docs/AttributeReference.html#dllexport) when building for Windows. I haven't added an equivalent check for `dllimport`, as we weren't actually using the result of that check, we're just testing that `MSC_VER` was defined before using.
With these changes building a libbitcoinconsensus with reduced exports, when targeting Darwin, works as expected:
```bash
./autogen.sh
./configure --disable-tests --disable-bench --with-utils=no --with-daemon=no --with-gui=no --disable-wallet --with-libs=yes --enable-reduce-exports
make -j8
...
nm -C src/.libs/libbitcoinconsensus.dylib | rg _bitcoinconsensus_
000000000000a340 T _bitcoinconsensus_verify_script
00000000000097e0 T _bitcoinconsensus_verify_script_with_amount
000000000000a3c0 T _bitcoinconsensus_version
```
```python
>>> import ctypes
>>> consensus = ctypes.CDLL("src/.libs/libbitcoinconsensus.dylib")
>>> print(consensus.bitcoinconsensus_version())
1
>>> exit()
```
TODO: Modify a CI job to compile with --enable-reduce-exports and check for symbols in shared lib?
ACKs for top commit:
laanwj:
Code review ACK de4238f92f4c067f099663f68d9772105de81d75
Tree-SHA512: d148f3c55d14dac6e9e5b718cc65bb557bcf6f663218d24bc9044b86281bd5dd3d931ebea79c336a58e8ed50d683218c0a9e75494f2267b91097665043e252ae
318c7263d0