Since 4c0d8d9673, most dlopen notes are
set at the beginning of the executables. Let's manage all dlopen notes
there, rather than setting them where dlopen is called.
Note that the only exceptions are the LIBBPF_NOTE for networkd and
nsresource. Since dlopen_bpf() is wrapped in an `#if` guard, the notes
are instead set within the corresponding functionality.
As a result, the DLOPEN_FOO() wrapper macros are no longer needed and
can be dropped completely.
When compiler optimization or LTO (Link Time Optimization) is enabled,
dlopen helper functions (such as dlopen_libfoo()) can be aggressively
inlined into their callers or cloned for specific call sites.
While this is beneficial for production builds, it alters or completely
removes the original function symbols from the final executable.
Consequently, this breaks the test (to be added in this series) that
checks whether the dlopen_libfoo() function corresponding to a dlopen
ELF note is actually called.
To resolve this, introduce the `_dlopen_loader_` macro. Under developer
builds, it applies the `_noclone_` and `_noinline_` attributes to guarantee
that helper symbols remain intact and discoverable by the test suite. In
production builds, the macro evaluates to nothing, allowing full compiler
optimization to proceed unimpeded.
This also switches all these notes to be defined via SD_ELF_NOTE_DLOPEN_ANCHORED().
Consequently, any notes added within unreachable or unused functions will be
automatically garbage-collected by the linker (--gc-sections) instead of
bloating the final binary.
E.g. unused p11-kit library dependency is now dropped from
systemd-repart.standalone binary.
Before:
```
$ systemd-analyze dlopen-metadata build/systemd-repart.standalone
FEATURE DESCRIPTION SONAME PRIORITY
cryptsetup Support for disk encryption, integrity, and authentication libcryptsetup.so.12 recommended
blkid Support for block device identification libblkid.so.1 required
libcrypto Support for cryptographic operations libcrypto.so.4 libcrypto.so.3 recommended
mount Support for mount enumeration libmount.so.1 required
fdisk Support for reading and writing partition tables libfdisk.so.1 required
blkid Support for block device identification libblkid.so.1 recommended
libcrypto Support for cryptographic operations libcrypto.so.4 libcrypto.so.3 suggested
cryptsetup Support for disk encryption, integrity, and authentication libcryptsetup.so.12 suggested
fdisk Support for reading and writing partition tables libfdisk.so.1 suggested
idn Support for internationalized domain names libidn2.so.0 suggested
mount Support for mount enumeration libmount.so.1 recommended
selinux Support for SELinux libselinux.so.1 recommended
tpm Support for TPM libtss2-esys.so.0 suggested
tpm Support for TPM libtss2-rc.so.0 suggested
tpm Support for TPM libtss2-mu.so.0 suggested
tpm Support for TPM libtss2-tcti-device.so.0 suggested
p11-kit Support for PKCS11 hardware tokens libp11-kit.so.0 suggested
```
After:
```
$ systemd-analyze dlopen-metadata build/systemd-repart.standalone
FEATURE DESCRIPTION SONAME PRIORITY
cryptsetup Support for disk encryption, integrity, and authentication libcryptsetup.so.12 recommended
blkid Support for block device identification libblkid.so.1 required
libcrypto Support for cryptographic operations libcrypto.so.4 libcrypto.so.3 recommended
mount Support for mount enumeration libmount.so.1 required
fdisk Support for reading and writing partition tables libfdisk.so.1 required
blkid Support for block device identification libblkid.so.1 recommended
libcrypto Support for cryptographic operations libcrypto.so.4 libcrypto.so.3 suggested
cryptsetup Support for disk encryption, integrity, and authentication libcryptsetup.so.12 suggested
fdisk Support for reading and writing partition tables libfdisk.so.1 suggested
mount Support for mount enumeration libmount.so.1 recommended
selinux Support for SELinux libselinux.so.1 recommended
tpm Support for TPM libtss2-esys.so.0 suggested
tpm Support for TPM libtss2-rc.so.0 suggested
tpm Support for TPM libtss2-mu.so.0 suggested
tpm Support for TPM libtss2-tcti-device.so.0 suggested
```
This makes each `foo_cflags` dependency define a `SYSTEMD_CFLAGS_MARKER_FOO`
macro, and checks if the macro is set when headers provided by external
libraries are included.
With this, we can fail fast at compile time if necessary `_cflags`
dependencies are omitted in meson.build. Missing dependencies found by this
mechanism have been added across the tree.
This macro emits an SD_ELF_NOTE_DLOPEN note so that calling sites,
and not just libsystemd-shared, get the ELF stamped with the notes
documenting the dependency. Currently most of the dlopen notes end
up in libsystemd-shared, and executables have no way to document
the optional dependencies they need. With this new macro, this
issue can be fixed.
Co-developed-by: Claude Opus 4.8 <noreply@anthropic.com>
Convert the GnuTLS and libmicrohttpd usage in journal-remote to the
dlopen pattern used by other optional shared libraries. A new
src/shared/gnutls-util.{h,c} declares the GnuTLS entry points via
DLSYM_PROTOTYPE and resolves them in dlopen_gnutls(); microhttpd-util
is moved from src/journal-remote to src/shared and gains analogous
DLSYM_PROTOTYPEs plus dlopen_microhttpd(). Callers in journal-gatewayd,
journal-remote-main and microhttpd-util itself call the sym_* wrappers
and invoke dlopen_gnutls()/dlopen_microhttpd() at their entry points.
setup_gnutls_logger() no longer fails when libgnutls is missing at
runtime; it logs a notice and returns 0 so journal-gatewayd starts up
without TLS dependencies installed.
The meson files gain libgnutls_cflags and libmicrohttpd_cflags partial
dependencies that expose include paths and compile flags only. Every
systemd-journal-{gatewayd,remote,upload} target switches to the cflags
variant, dropping the direct libgnutls/libmicrohttpd link. The
gatewayd->remote object-sharing dance for microhttpd-util.o goes away
since the code now lives in libshared.
test-dlopen-so gains assertions for dlopen_gnutls and dlopen_microhttpd.
Yu Watanabe
Luca Boccassi
Daan De Meyer