5fa970e868f25ebc79ccca9b1d9df4c030d97661 — Fangrui Song 2 years ago 660a68b
LLD 13 and GNU ld 2.37 support -z start-stop-gc which allows garbage
collection of C identifier name sections despite the __start_/__stop_
references.  Simply set the retain attribute so that GCC 11 (if
configure-time binutils is 2.36 or newer)/Clang 13 will set the
SHF_GNU_RETAIN section attribute to prevent garbage collection.

Without the patch, there are linker errors like the following with -z

ld: error: undefined symbol: __start_SYSTEMD_BUS_ERROR_MAP
>>> referenced by bus-error.c:93 (../src/libsystemd/sd-bus/bus-error.c:93)
>>>               sd-bus_bus-error.c.o:(bus_error_name_to_errno) in archive src/libsystemd/libsystemd_static.a

Co-authored-by: Evgeniy Khramtsov <evgeniy@khramtsov.org>
1 files changed, 6 insertions(+), 0 deletions(-)

M src/libsystemd/sd-bus/bus-error.h
M src/libsystemd/sd-bus/bus-error.h => src/libsystemd/sd-bus/bus-error.h +6 -0
@@ 28,11 28,17 @@ int bus_error_set_errnofv(sd_bus_error *e, int error, const char *format, va_lis
 * the bus error table, and BUS_ERROR_MAP_ELF_USE has to be used at
 * least once per compilation unit (i.e. per library), to ensure that
 * the error map is really added to the final binary.
 * In addition, set the retain attribute so that the section cannot be
 * discarded by ld --gc-sections -z start-stop-gc. Older compilers would
 * warn for the unknown attribute, so just disable -Wattributes.

#define BUS_ERROR_MAP_ELF_REGISTER                                      \
        _Pragma("GCC diagnostic ignored \"-Wattributes\"")              \
        __attribute__ ((__section__("BUS_ERROR_MAP")))                  \
        __attribute__ ((__used__))                                      \
        __attribute__ ((retain))                                        \
        __attribute__ ((aligned(8)))

#define BUS_ERROR_MAP_ELF_USE(errors)                                   \