mpgen: Work around c++20 / capnproto 0.8 incompatibility #194

ryanofsky · 2025-08-12T20:20:51Z

Fix ubuntu 22.04 compatibility issue reported by fanquake in bitcoin/bitcoin#33176 and add CI job to make sure libmultiprocess stays compatible with old versions of Cap'n Proto.

Changes are described in more detail in commit messages.

DrahtBot · 2025-08-12T20:20:58Z

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ryanofsky · 2025-08-12T21:50:12Z

Updated 151ef65 -> c659685 (pr/string.1 -> pr/string.2, compare) testing some more intermediate versions
Updated c659685 -> 88d9504 (pr/string.2 -> pr/string.3, compare) adding missing file

Sjors · 2025-08-13T09:36:11Z

shell.nix

+      rev   = "v${capnprotoVersion}";
+      hash  = lib.attrByPath [capnprotoVersion] "" capnprotoHashes;
+    };
+    patches = lib.optionals (lib.versionAtLeast capnprotoVersion "0.9.0" && lib.versionOlder capnprotoVersion "0.10.4") [ ./ci/patches/spaceship.patch ];


88d9504: do I read this correctly as: apply patch to versions 0.9.0 <= ... < 0.10.4?

re: #194 (comment)

88d9504: do I read this correctly as: apply patch to versions 0.9.0 <= ... < 0.10.4?

Yes that's right. These versions of capnproto added some c++20 support which didn't actually work with later compiler versions.

Sjors · 2025-08-13T09:38:39Z

utACK 88d9504

The kj/string.h header installed by capnproto 0.8 doesn't work well when compiling with -std=c++20 or later because the reverse StringPtr/char* comparison function it provides is broken in c++20: inline bool operator==(const char* a, const StringPtr& b) { return b == a; } Before C++20 this would implicitly convert `a` to a StringPtr and call the StringPtr::operator== method. But starting with C++20 it actually calls itself recursively and either loops forever or crashes. This problem was fixed upstream by capnproto/capnproto#1170 in Cap'n Proto 0.9.0. Avoid the problem here for older versions by just not using the operator. A CI job testing older versions is added in the next commit to avoid similar breakage in the future.

The CI job currently just tests old Cap'n Proto versions, but it might be nice to extend in the future to test old compilers & build tools too. Support for versions of Cap'n Proto before 0.7.0 was dropped in bitcoin-core#88 in order to avoid compiler warnings and simplify code. Before that, versions back to 0.5 were supported and are basically still compatible since the Cap'n Proto API hasn't changed and libmultiprocess does not rely on newer features.

30930df build: require CapnProto 0.7.0 or better (Sjors Provoost) Pull request description: Although 1.0.1. is the oldest version currently covered by Bitcoin Core's extensive CI, Debian Bookwork ships 0.9.2 and #194 introduces test coverage for even older versions. 0.7 has been required since #88. The CI run of Sjors/bitcoin#100 @ [3d55222](https://github.com/Sjors/bitcoin/pull/100/checks?sha=3d552223712eed88d17e5ead1ef7d1ba6fd7e89e) previously checked Bitcoin Core CI against 1.0.1 as the minimum. Lowering the minimum further should not be a problem for that CI. ACKs for top commit: ryanofsky: Code review ACK 30930df. Planning to follow up in #194 to actually test minimum version and error if capnproto version detected is affected by CVE-2022-46149 Tree-SHA512: bed5843973c8ff1f0b2bd93efe7169824c2306097efefaace1752efeb06606df765b68b7ef50c07f5d703010c4d1b324099d6780fa0363e126d34ac1307fba1a

Also document minimum Cap'n Proto version in doc/install.md

ryanofsky

Rebased 88d9504 -> dc3ba22 (pr/string.3 -> pr/string.4, compare) on top of #193 and added explicit check for CVE-2022-46149

ryanofsky · 2025-08-13T10:19:56Z

shell.nix

+      rev   = "v${capnprotoVersion}";
+      hash  = lib.attrByPath [capnprotoVersion] "" capnprotoHashes;
+    };
+    patches = lib.optionals (lib.versionAtLeast capnprotoVersion "0.9.0" && lib.versionOlder capnprotoVersion "0.10.4") [ ./ci/patches/spaceship.patch ];


re: #194 (comment)

88d9504: do I read this correctly as: apply patch to versions 0.9.0 <= ... < 0.10.4?

Yes that's right. These versions of capnproto added some c++20 support which didn't actually work with later compiler versions.

Sjors · 2025-08-13T13:34:30Z

utACK dc3ba22

Thanks for adding the CVE version check.

TheCharlatan

ACK dc3ba22

maflcko · 2025-08-19T14:21:43Z

CMakeLists.txt

+   OR CapnProto_VERSION STREQUAL "0.10.0"
+   OR CapnProto_VERSION STREQUAL "0.10.1"
+   OR CapnProto_VERSION STREQUAL "0.10.2")
+  message(FATAL_ERROR


isn't ipc a trusted interface, where anyone having access can already fully control the process (like calling createTransaction), so leaking memory should not make anything worse? A warning seems fine here? Also, a cve check seems a bit unrelated from a C++20 code workaround (from the title).

Just a nit and not a blocker, but I wanted to mention it, since this will lead to a compile error on Ubuntu 22.04 (bitcoin/bitcoin#33176 (comment)), for an option that will be enabled by default?

For ubuntu 22.04 if this will create confusion, I feel like a good solution might be to improve error message and documentation to specifically suggest disabling ENABLE_IPC, or installing a newer version of capnproto. Ideally it seems like ubuntu could update from 0.8.0 to 0.8.1 given 0.8.1 was released to fix the CVE and doesn't have any other changes.

On IPC being a trusted interface, it's definitely true with the current interface, a malicious client could do a lot of things to crash the node and maybe even take control of it. But this doesn't have to be the case. We could provide capnproto interfaces that do rigorously check all their inputs and enforce resource constraints. It would even be possible to adapt the Mining interface to do this, but it hasn't been a reason to make the extra effort. I also feel like showing an error after discovering a package with a CVE is kind of a public service, since we don't know if there may be other software using the package.

Currently the version of capnproto on Debian 12, 0.9.2, does not play well with `mpgen` used by recently-merged multiprocess PR #31802. This is currently being worked on: bitcoin-core/libmultiprocess#194 ... but in the meantime bump Debian versions to fix.

ryanofsky · 2025-08-22T21:20:19Z

src/mp/gen.cpp

In commit "mpgen: Work around c++20 / capnproto 0.8 incompatibility" (c4cb758)

I think commit message is wrong in suggesting that with c++20 the operator== function is buggy and will call itself recursively. It seems the reason this happens is not really because of c++20 but because of a gcc bug https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53499. See also bitcoin/bitcoin#33176 (comment)

…6f1e54 1b8d4a6f1e54 Merge bitcoin-core/libmultiprocess#194: mpgen: Work around c++20 / capnproto 0.8 incompatibility f1fad396bf5f Merge bitcoin-core/libmultiprocess#195: ci: Add openbsd eed42f210d17 ci: Bump all tasks to actions/checkout@v5 486a510bbeff ci: Remove ancient and problematic -lstdc++fs in mpexample dd40897efe79 Add missing thread include 98414e7d2867 ci: Add openbsd dc3ba2204606 cmake, doc: Add check for CVE-2022-46149 cb170d4913a2 Merge bitcoin-core/libmultiprocess#193: build: require CapnProto 0.7.0 or better 8ceeaa6ae401 ci: Add olddeps job to test old dependencies versions c4cb758eccb5 mpgen: Work around c++20 / capnproto 0.8 incompatibility 30930dff7b06 build: require CapnProto 0.7.0 or better git-subtree-dir: src/ipc/libmultiprocess git-subtree-split: 1b8d4a6f1e54b92708bd2ad627ec6d440a1daf3d

1b8d4a6f1e Merge bitcoin-core/libmultiprocess#194: mpgen: Work around c++20 / capnproto 0.8 incompatibility f1fad396bf Merge bitcoin-core/libmultiprocess#195: ci: Add openbsd eed42f210d ci: Bump all tasks to actions/checkout@v5 486a510bbe ci: Remove ancient and problematic -lstdc++fs in mpexample dd40897efe Add missing thread include 98414e7d28 ci: Add openbsd dc3ba22046 cmake, doc: Add check for CVE-2022-46149 cb170d4913 Merge bitcoin-core/libmultiprocess#193: build: require CapnProto 0.7.0 or better 8ceeaa6ae4 ci: Add olddeps job to test old dependencies versions c4cb758ecc mpgen: Work around c++20 / capnproto 0.8 incompatibility 30930dff7b build: require CapnProto 0.7.0 or better git-subtree-dir: src/ipc/libmultiprocess git-subtree-split: 1b8d4a6f1e54b92708bd2ad627ec6d440a1daf3d

dd68d0f Squashed 'src/ipc/libmultiprocess/' changes from b4120d34bad2..1b8d4a6f1e54 (Ryan Ofsky) Pull request description: Includes: - bitcoin-core/libmultiprocess#193 - bitcoin-core/libmultiprocess#195 - bitcoin-core/libmultiprocess#194 These changes are needed to build fix libmultiprocess build issue that happens on OpenBSD and work around an incompatibility between GCC versions <14 and cap'nproto versions <0.9 when compiling with c++20 that was fixed upstream in capnproto/capnproto#1170. The issues were reported: - #33219 - #33176 - willcl-ark/bitcoin-core-docker#43 The fixes added CI jobs upstream to catch these issues earlier. The changes can be verified by running `test/lint/git-subtree-check.sh src/ipc/libmultiprocess` as described in [developer notes](https://github.com/bitcoin/bitcoin/blob/master/doc/developer-notes.md#subtrees) and [lint instructions](https://github.com/bitcoin/bitcoin/tree/master/test/lint#git-subtree-checksh) ACKs for top commit: Sjors: ACK 323b3fd achow101: ACK 323b3fd hebasto: ACK 323b3fd, I've reproduced the subtree update locally. The two issues noted in this PR are unrelated to its changes and can be addressed separately. Tree-SHA512: 3d03693d269c04d9ed10e8dd03e8059062929f37616d974c6fdf346ee62737c990ec550e013575e7474bfa4efcead3938bf9b259d62c073d76e720ebafe4ff66

willcl-ark · 2025-09-01T10:34:32Z

I'm not sure, as you say this was fixed upstream in v0.9 , but I think I might still be hitting this on debian bookworm with 0.9.2?:

<snip>

-- Checking for module 'capnp'
--   Found capnp, version 0.9.2
-- Checking for module 'capnpc'
--   Found capnpc, version 0.9.2
-- Checking for module 'capnp-rpc'
--   Found capnp-rpc, version 0.9.2
-- Checking for module 'capnp-json'
--   Found capnp-json, version 0.9.2
-- Checking for module 'capnp-websocket'
--   Found capnp-websocket, version 0.9.2
-- Checking for module 'kj'
--   Found kj, version 0.9.2
-- Checking for module 'kj-async'
--   Found kj-async, version 0.9.2
-- Checking for module 'kj-http'
--   Found kj-http, version 0.9.2
-- Checking for module 'kj-gzip'
--   Found kj-gzip, version 0.9.2
-- Checking for module 'kj-tls'
--   Found kj-tls, version 0.9.2
-- Checking for module 'kj-test'
--   Found kj-test, version 0.9.2

<snip>

C++ compiler .......................... Clang 19.1.4, /usr/bin/clang++-19
CMAKE_BUILD_TYPE ...................... RelWithDebInfo
Preprocessor defined macros ...........
C++ compiler flags .................... -O2 -g -std=c++20 -fPIC -fdebug-prefix-map=/src/bitcoin/src=. -fmacro-prefix-map=/src/bitcoin/src=. -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=3 -Wstack-protector -fstack-protector-all -fcf-protection=full -fstack-clash-protection -Wall -Wextra -Wgnu -Wformat -Wformat-security -Wvla -Wshadow-field -Wthread-safety -Wloop-analysis -Wredundant-decls -Wunused-member-function -Wdate-time -Wconditional-uninitialized -Woverloaded-virtual -Wsuggest-override -Wimplicit-fallthrough -Wunreachable-code -Wdocumentation -Wself-assign -Wundef -Wno-unused-parameter
Linker flags .......................... -O2 -g -fstack-protector-all -fcf-protection=full -fstack-clash-protection -Wl,-z,relro -Wl,-z,now -Wl,-z,separate-code -fPIE -pie

<snip>

In file included from /src/bitcoin/src/ipc/libmultiprocess/src/mp/util.cpp:6:
In file included from /src/bitcoin/src/ipc/libmultiprocess/include/mp/util.h:8:
In file included from /usr/include/capnp/schema.h:39:
In file included from /usr/include/capnp/schema.capnp.h:6:
In file included from /usr/include/capnp/generated-header-support.h:27:
In file included from /usr/include/capnp/layout.h:34:
/usr/include/capnp/blob.h:176:74: error: invalid operands to binary expression ('const char *' and 'kj::StringPtr')
  176 | inline bool operator==(const char* a, const Text::Builder& b) { return a == b.asString(); }
      |                                                                        ~ ^  ~~~~~~~~~~~~
/usr/include/kj/common.h:744:13: note: candidate function template not viable: no known conversion from 'kj::StringPtr' to 'MaxValue_' for 2nd argument
  744 | inline bool operator==(T t, MaxValue_) { return t == Decay<T>(maxValue); }
      |             ^               ~~~~~~~~~
/usr/include/kj/common.h:746:13: note: candidate function template not viable: no known conversion from 'kj::StringPtr' to 'MinValue_' for 2nd argument
  746 | inline bool operator==(T t, MinValue_) { return t == Decay<T>(minValue); }
      |             ^               ~~~~~~~~~
/usr/include/capnp/blob.h:176:13: note: candidate function not viable: no known conversion from 'kj::StringPtr' to 'const Text::Builder' for 2nd argument
  176 | inline bool operator==(const char* a, const Text::Builder& b) { return a == b.asString(); }
      |             ^                         ~~~~~~~~~~~~~~~~~~~~~~
/usr/include/kj/common.h:744:13: note: candidate function (with reversed parameter order) template not viable: no known conversion from 'const char *' to 'MaxValue_' for 1st argument
  744 | inline bool operator==(T t, MaxValue_) { return t == Decay<T>(maxValue); }
      |             ^          ~~~
/usr/include/kj/common.h:746:13: note: candidate function (with reversed parameter order) template not viable: no known conversion from 'const char *' to 'MinValue_' for 1st argument
  746 | inline bool operator==(T t, MinValue_) { return t == Decay<T>(minValue); }
      |             ^          ~~~
/usr/include/capnp/blob.h:176:13: note: candidate function (with reversed parameter order) not viable: no known conversion from 'const char *' to 'const Text::Builder' for 1st argument
  176 | inline bool operator==(const char* a, const Text::Builder& b) { return a == b.asString(); }
      |             ^          ~~~~~~~~~~~~~
/usr/include/capnp/blob.h:177:74: error: invalid operands to binary expression ('const char *' and 'kj::StringPtr')
  177 | inline bool operator!=(const char* a, const Text::Builder& b) { return a != b.asString(); }
      |                                                                        ~ ^  ~~~~~~~~~~~~
/usr/include/kj/common.h:744:13: note: candidate function template not viable: no known conversion from 'kj::StringPtr' to 'MaxValue_' for 2nd argument
  744 | inline bool operator==(T t, MaxValue_) { return t == Decay<T>(maxValue); }
      |             ^               ~~~~~~~~~
/usr/include/kj/common.h:746:13: note: candidate function template not viable: no known conversion from 'kj::StringPtr' to 'MinValue_' for 2nd argument
  746 | inline bool operator==(T t, MinValue_) { return t == Decay<T>(minValue); }
      |             ^               ~~~~~~~~~
/usr/include/capnp/blob.h:176:13: note: candidate function not viable: no known conversion from 'kj::StringPtr' to 'const Text::Builder' for 2nd argument
  176 | inline bool operator==(const char* a, const Text::Builder& b) { return a == b.asString(); }
      |             ^                         ~~~~~~~~~~~~~~~~~~~~~~
/usr/include/capnp/blob.h:177:13: note: candidate function not viable: no known conversion from 'kj::StringPtr' to 'const Text::Builder' for 2nd argument
  177 | inline bool operator!=(const char* a, const Text::Builder& b) { return a != b.asString(); }
      |             ^                         ~~~~~~~~~~~~~~~~~~~~~~
/usr/include/kj/common.h:744:13: note: candidate function (with reversed parameter order) template not viable: no known conversion from 'const char *' to 'MaxValue_' for 1st argument
  744 | inline bool operator==(T t, MaxValue_) { return t == Decay<T>(maxValue); }
      |             ^          ~~~
/usr/include/kj/common.h:746:13: note: candidate function (with reversed parameter order) template not viable: no known conversion from 'const char *' to 'MinValue_' for 1st argument
  746 | inline bool operator==(T t, MinValue_) { return t == Decay<T>(minValue); }
      |             ^          ~~~
2 errors generated.
gmake[2]: *** [src/ipc/libmultiprocess/CMakeFiles/mputil.dir/build.make:76: src/ipc/libmultiprocess/CMakeFiles/mputil.dir/src/mp/util.cpp.o] Error 1
gmake[1]: *** [CMakeFiles/Makefile2:900: src/ipc/libmultiprocess/CMakeFiles/mputil.dir/all] Error 2
gmake[1]: *** Waiting for unfinished jobs....

log.txt

May also be a different issue (in which case I can open a new issue here or in bitcoin/bitcoin if that would be more appropriate).

maflcko · 2025-09-01T11:12:24Z

I'm not sure, as you say this was fixed upstream in v0.9 , but I think I might still be hitting this on debian bookworm with 0.9.2?:

Yeah, to reproduce:

diff --git a/ci/configs/openbsd.bash b/ci/configs/openbsd.bash
index a404e2b..70ae010 100644
--- a/ci/configs/openbsd.bash
+++ b/ci/configs/openbsd.bash
@@ -1,5 +1,6 @@
 CI_DESC="CI config for OpenBSD"
 CI_DIR=build-openbsd
+export CXX=clang++-16
 export CXXFLAGS="-Werror -Wall -Wextra -Wpedantic -Wno-unused-parameter"
 CMAKE_ARGS=(-G Ninja)
 BUILD_ARGS=(-k 0)

And (on debian:bookworm !):

# CI_CLEAN=1 CI_CONFIG="ci/configs/openbsd.bash" bash ci/scripts/ci.sh 
+ '[' x ']'
+ source ci/configs/openbsd.bash
++ CI_DESC='CI config for OpenBSD'
++ CI_DIR=build-openbsd
++ export CXX=clang++-16
++ CXX=clang++-16
++ export 'CXXFLAGS=-Werror -Wall -Wextra -Wpedantic -Wno-unused-parameter'
++ CXXFLAGS='-Werror -Wall -Wextra -Wpedantic -Wno-unused-parameter'
++ CMAKE_ARGS=(-G Ninja)
++ BUILD_ARGS=(-k 0)
+ : build-openbsd
+ '[' -v BUILD_TARGETS ']'
+ BUILD_TARGETS=(all tests mpexamples)
+ '[' -n 1 ']'
+ rm -rf build-openbsd
+ cmake -B build-openbsd -G Ninja
-- The CXX compiler identification is Clang 16.0.6
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/clang++-16 - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE  
-- Found OpenSSL: /usr/lib/x86_64-linux-gnu/libcrypto.so (found version "3.0.17") found components: Crypto SSL 
-- Found PkgConfig: /usr/bin/pkg-config (found version "1.8.1") 
-- Checking for module 'capnp'
--   Found capnp, version 0.9.2
-- Checking for module 'capnpc'
--   Found capnpc, version 0.9.2
-- Checking for module 'capnp-rpc'
--   Found capnp-rpc, version 0.9.2
-- Checking for module 'capnp-json'
--   Found capnp-json, version 0.9.2
-- Checking for module 'capnp-websocket'
--   Found capnp-websocket, version 0.9.2
-- Checking for module 'kj'
--   Found kj, version 0.9.2
-- Checking for module 'kj-async'
--   Found kj-async, version 0.9.2
-- Checking for module 'kj-http'
--   Found kj-http, version 0.9.2
-- Checking for module 'kj-gzip'
--   Found kj-gzip, version 0.9.2
-- Checking for module 'kj-tls'
--   Found kj-tls, version 0.9.2
-- Checking for module 'kj-test'
--   Found kj-test, version 0.9.2
-- Performing Test HAVE_PTHREAD_GETNAME_NP
-- Performing Test HAVE_PTHREAD_GETNAME_NP - Success
-- Performing Test HAVE_PTHREAD_THREADID_NP
-- Performing Test HAVE_PTHREAD_THREADID_NP - Failed
-- Performing Test HAVE_PTHREAD_GETTHREADID_NP
-- Performing Test HAVE_PTHREAD_GETTHREADID_NP - Failed
-- Configuring done
-- Generating done
-- Build files have been written to: /libmultiprocess/build-openbsd
+ cmake --build build-openbsd -t all tests mpexamples -- -k 0
[1/59] Building CXX object CMakeFiles/mputil.dir/src/mp/util.cpp.o
FAILED: CMakeFiles/mputil.dir/src/mp/util.cpp.o 
/usr/bin/clang++-16  -I/libmultiprocess/include -I/libmultiprocess/build-openbsd/include -Werror -Wall -Wextra -Wpedantic -Wno-unused-parameter -std=gnu++20 -MD -MT CMakeFiles/mputil.dir/src/mp/util.cpp.o -MF CMakeFiles/mputil.dir/src/mp/util.cpp.o.d -o CMakeFiles/mputil.dir/src/mp/util.cpp.o -c /libmultiprocess/src/mp/util.cpp
In file included from /libmultiprocess/src/mp/util.cpp:6:
In file included from /libmultiprocess/include/mp/util.h:8:
In file included from /usr/include/capnp/schema.h:39:
In file included from /usr/include/capnp/schema.capnp.h:6:
In file included from /usr/include/capnp/generated-header-support.h:27:
In file included from /usr/include/capnp/layout.h:34:
/usr/include/capnp/blob.h:176:74: error: invalid operands to binary expression ('const char *' and 'kj::StringPtr')
inline bool operator==(const char* a, const Text::Builder& b) { return a == b.asString(); }
                                                                       ~ ^  ~~~~~~~~~~~~
/usr/include/kj/common.h:744:13: note: candidate function template not viable: no known conversion from 'kj::StringPtr' to 'MaxValue_' for 2nd argument
inline bool operator==(T t, MaxValue_) { return t == Decay<T>(maxValue); }
            ^
/usr/include/kj/common.h:744:13: note: candidate function (with reversed parameter order) template not viable: no known conversion from 'const char *' to 'MaxValue_' for 1st argument
/usr/include/kj/common.h:746:13: note: candidate function template not viable: no known conversion from 'kj::StringPtr' to 'MinValue_' for 2nd argument
inline bool operator==(T t, MinValue_) { return t == Decay<T>(minValue); }
            ^
/usr/include/kj/common.h:746:13: note: candidate function (with reversed parameter order) template not viable: no known conversion from 'const char *' to 'MinValue_' for 1st argument
/usr/include/capnp/blob.h:176:13: note: candidate function not viable: no known conversion from 'kj::StringPtr' to 'const Text::Builder' for 2nd argument
inline bool operator==(const char* a, const Text::Builder& b) { return a == b.asString(); }
            ^                                                               ~~~~~~~~~~~~
/usr/include/capnp/blob.h:176:13: note: candidate function (with reversed parameter order) not viable: no known conversion from 'const char *' to 'const Text::Builder' for 1st argument
inline bool operator==(const char* a, const Text::Builder& b) { return a == b.asString(); }
            ^                                                          ~
/usr/include/capnp/blob.h:177:74: error: invalid operands to binary expression ('const char *' and 'kj::StringPtr')
inline bool operator!=(const char* a, const Text::Builder& b) { return a != b.asString(); }
                                                                       ~ ^  ~~~~~~~~~~~~
/usr/include/kj/common.h:744:13: note: candidate function template not viable: no known conversion from 'kj::StringPtr' to 'MaxValue_' for 2nd argument
inline bool operator==(T t, MaxValue_) { return t == Decay<T>(maxValue); }
            ^
/usr/include/kj/common.h:744:13: note: candidate function (with reversed parameter order) template not viable: no known conversion from 'const char *' to 'MaxValue_' for 1st argument
/usr/include/kj/common.h:746:13: note: candidate function template not viable: no known conversion from 'kj::StringPtr' to 'MinValue_' for 2nd argument
inline bool operator==(T t, MinValue_) { return t == Decay<T>(minValue); }
            ^
/usr/include/kj/common.h:746:13: note: candidate function (with reversed parameter order) template not viable: no known conversion from 'const char *' to 'MinValue_' for 1st argument
/usr/include/capnp/blob.h:176:13: note: candidate function not viable: no known conversion from 'kj::StringPtr' to 'const Text::Builder' for 2nd argument
inline bool operator==(const char* a, const Text::Builder& b) { return a == b.asString(); }
            ^
/usr/include/capnp/blob.h:177:13: note: candidate function not viable: no known conversion from 'kj::StringPtr' to 'const Text::Builder' for 2nd argument
inline bool operator!=(const char* a, const Text::Builder& b) { return a != b.asString(); }
            ^                                                               ~~~~~~~~~~~~
2 errors generated.
[2/59] Building CXX object CMakeFiles/mpgen.dir/src/mp/gen.cpp.o
FAILED: CMakeFiles/mpgen.dir/src/mp/gen.cpp.o 
/usr/bin/clang++-16  -I/libmultiprocess/build-openbsd/include -I/libmultiprocess/include -Werror -Wall -Wextra -Wpedantic -Wno-unused-parameter -std=gnu++20 -MD -MT CMakeFiles/mpgen.dir/src/mp/gen.cpp.o -MF CMakeFiles/mpgen.dir/src/mp/gen.cpp.o.d -o CMakeFiles/mpgen.dir/src/mp/gen.cpp.o -c /libmultiprocess/src/mp/gen.cpp
In file included from /libmultiprocess/src/mp/gen.cpp:6:
In file included from /libmultiprocess/include/mp/util.h:8:
In file included from /usr/include/capnp/schema.h:39:
In file included from /usr/include/capnp/schema.capnp.h:6:
In file included from /usr/include/capnp/generated-header-support.h:27:
In file included from /usr/include/capnp/layout.h:34:
/usr/include/capnp/blob.h:176:74: error: invalid operands to binary expression ('const char *' and 'kj::StringPtr')
inline bool operator==(const char* a, const Text::Builder& b) { return a == b.asString(); }
                                                                       ~ ^  ~~~~~~~~~~~~
/usr/include/kj/common.h:744:13: note: candidate function template not viable: no known conversion from 'kj::StringPtr' to 'MaxValue_' for 2nd argument
inline bool operator==(T t, MaxValue_) { return t == Decay<T>(maxValue); }
            ^
/usr/include/kj/common.h:744:13: note: candidate function (with reversed parameter order) template not viable: no known conversion from 'const char *' to 'MaxValue_' for 1st argument
/usr/include/kj/common.h:746:13: note: candidate function template not viable: no known conversion from 'kj::StringPtr' to 'MinValue_' for 2nd argument
inline bool operator==(T t, MinValue_) { return t == Decay<T>(minValue); }
            ^
/usr/include/kj/common.h:746:13: note: candidate function (with reversed parameter order) template not viable: no known conversion from 'const char *' to 'MinValue_' for 1st argument
/usr/include/capnp/blob.h:176:13: note: candidate function not viable: no known conversion from 'kj::StringPtr' to 'const Text::Builder' for 2nd argument
inline bool operator==(const char* a, const Text::Builder& b) { return a == b.asString(); }
            ^                                                               ~~~~~~~~~~~~
/usr/include/capnp/blob.h:176:13: note: candidate function (with reversed parameter order) not viable: no known conversion from 'const char *' to 'const Text::Builder' for 1st argument
inline bool operator==(const char* a, const Text::Builder& b) { return a == b.asString(); }
            ^                                                          ~
/usr/include/capnp/blob.h:177:74: error: invalid operands to binary expression ('const char *' and 'kj::StringPtr')
inline bool operator!=(const char* a, const Text::Builder& b) { return a != b.asString(); }
                                                                       ~ ^  ~~~~~~~~~~~~
/usr/include/kj/common.h:744:13: note: candidate function template not viable: no known conversion from 'kj::StringPtr' to 'MaxValue_' for 2nd argument
inline bool operator==(T t, MaxValue_) { return t == Decay<T>(maxValue); }
            ^
/usr/include/kj/common.h:744:13: note: candidate function (with reversed parameter order) template not viable: no known conversion from 'const char *' to 'MaxValue_' for 1st argument
/usr/include/kj/common.h:746:13: note: candidate function template not viable: no known conversion from 'kj::StringPtr' to 'MinValue_' for 2nd argument
inline bool operator==(T t, MinValue_) { return t == Decay<T>(minValue); }
            ^
/usr/include/kj/common.h:746:13: note: candidate function (with reversed parameter order) template not viable: no known conversion from 'const char *' to 'MinValue_' for 1st argument
/usr/include/capnp/blob.h:176:13: note: candidate function not viable: no known conversion from 'kj::StringPtr' to 'const Text::Builder' for 2nd argument
inline bool operator==(const char* a, const Text::Builder& b) { return a == b.asString(); }
            ^
/usr/include/capnp/blob.h:177:13: note: candidate function not viable: no known conversion from 'kj::StringPtr' to 'const Text::Builder' for 2nd argument
inline bool operator!=(const char* a, const Text::Builder& b) { return a != b.asString(); }
            ^                                                               ~~~~~~~~~~~~
2 errors generated.
ninja: build stopped: cannot make progress due to previous errors.

ryanofsky · 2025-09-01T14:16:04Z

re: @willcl-ark #194 (comment)

I'm not sure, as you say this was fixed upstream in v0.9 , but I think I might still be hitting this on debian bookworm with 0.9.2?:

If I'm interpreting correctly, debian bookworm uses clang 14 according to https://packages.debian.org/bookworm/clang so maybe doesn't have this issue by default, but I think you will run into this problem with clang-16 and newer. I made a new issue for this #199 so maybe we can figure out a solution there

…6f1e54 1b8d4a6f1e54 Merge bitcoin-core/libmultiprocess#194: mpgen: Work around c++20 / capnproto 0.8 incompatibility f1fad396bf5f Merge bitcoin-core/libmultiprocess#195: ci: Add openbsd eed42f210d17 ci: Bump all tasks to actions/checkout@v5 486a510bbeff ci: Remove ancient and problematic -lstdc++fs in mpexample dd40897efe79 Add missing thread include 98414e7d2867 ci: Add openbsd dc3ba2204606 cmake, doc: Add check for CVE-2022-46149 cb170d4913a2 Merge bitcoin-core/libmultiprocess#193: build: require CapnProto 0.7.0 or better 8ceeaa6ae401 ci: Add olddeps job to test old dependencies versions c4cb758eccb5 mpgen: Work around c++20 / capnproto 0.8 incompatibility 30930dff7b06 build: require CapnProto 0.7.0 or better git-subtree-dir: src/ipc/libmultiprocess git-subtree-split: 1b8d4a6f1e54b92708bd2ad627ec6d440a1daf3d

ryanofsky mentioned this pull request Aug 12, 2025

build: indefinite mpgen hang on Ubuntu 22.04 bitcoin/bitcoin#33176

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ryanofsky force-pushed the pr/string branch from 151ef65 to c659685 Compare August 12, 2025 21:49

ryanofsky force-pushed the pr/string branch from c659685 to 88d9504 Compare August 12, 2025 22:12

ryanofsky mentioned this pull request Aug 12, 2025

build: require CapnProto 0.7.0 or better #193

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Sjors mentioned this pull request Aug 13, 2025

Add bitcoin-{node,gui} to release binaries for IPC bitcoin/bitcoin#31802

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ryanofsky added 2 commits August 13, 2025 06:06

cmake, doc: Add check for CVE-2022-46149

dc3ba22

Also document minimum Cap'n Proto version in doc/install.md

ryanofsky force-pushed the pr/string branch from 88d9504 to dc3ba22 Compare August 13, 2025 10:13

ryanofsky commented Aug 13, 2025

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TheCharlatan approved these changes Aug 19, 2025

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willcl-ark mentioned this pull request Aug 21, 2025

Capnproto fixups willcl-ark/bitcoin-core-docker#43

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ryanofsky merged commit 1b8d4a6 into bitcoin-core:master Aug 22, 2025
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ryanofsky commented Aug 22, 2025

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ryanofsky mentioned this pull request Aug 22, 2025

Update libmultiprocess subtree to fix build issues bitcoin/bitcoin#33241

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ryanofsky mentioned this pull request Sep 1, 2025

Cap'n Proto 0.9 & 0.10 capnp/blob.h error: invalid operands to binary expression ('const char *' and 'kj::StringPtr') #199

Closed

mpgen: Work around c++20 / capnproto 0.8 incompatibility #194

mpgen: Work around c++20 / capnproto 0.8 incompatibility #194

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