- 

From 96ae9eb8abf5dc4b0686151142fe65b34ab45896 Mon Sep 17 00:00:00 2001

From: Fangrui Song <i@maskray.me>

Date: Sun, 28 Mar 2021 23:35:06 -0700

Subject: [PATCH] sd-bus: set retain attribute on BUS_ERROR_MAP_ELF_REGISTER

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

start-stop-gc.

```

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

```

---

 src/libsystemd/sd-bus/bus-error.h | 6 ++++++

 1 file changed, 6 insertions(+)

diff --git src/libsystemd/sd-bus/bus-error.h src/libsystemd/sd-bus/bus-error.h

index 06c478a..883213f 100644

--- src/libsystemd/sd-bus/bus-error.h

+++ src/libsystemd/sd-bus/bus-error.h

@@ -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)                                   \

-- 

2.32.0