From: Zbigniew Jędrzejewski-Szmek <zbyszek@amutable.com>
Date: Thu, 2 Apr 2026 20:20:48 +0000 (+0200)
Subject: meson: detect and use __attribute__((no_reorder))
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=fec559d034ed32929771c80922fd2c2249edba15;p=thirdparty%2Fsystemd.git

meson: detect and use __attribute__((no_reorder))

In some builds (package builds, so with optimization and lto, but I
haven't been able to pin down the exact combination on options that
matters), we end up with items in the verbs array reordered. The order
matters (because of groups, but also because we have some specific order
for display), so this reordering is something that we don't want.

From what I was able to read, the compiler + linker generally keep the
order within a single translation unit, but this is more of a convention
and implementation choice than a guarantee. Add this attribute [1]. It
seems to have the desired effect in CI.

[1] https://gcc.gnu.org/onlinedocs/gcc-15.2.0/gcc/Common-Function-Attributes.html#index-no_005freorder-function-attribute
---

diff --git a/meson.build b/meson.build
index c9e96b25914..0f8f0b5375a 100644
--- a/meson.build
+++ b/meson.build
@@ -549,6 +549,15 @@ foreach attr : possible_c_attributes
         conf.set10('HAVE_ATTRIBUTE_' + attr.to_upper(), have)
 endforeach
 
+# TODO: drop this manual check when meson learns about this attribute
+possible_c_attributes += ['no_reorder']
+
+have = cc.compiles(
+        '__attribute__((__no_reorder__)) int x;',
+        args : '-Werror=attributes',
+        name : '__attribute__((__no_reorder__))')
+conf.set10('HAVE_ATTRIBUTE_NO_REORDER', have)
+
 #####################################################################
 # compilation result tests
 
diff --git a/src/fundamental/macro-fundamental.h b/src/fundamental/macro-fundamental.h
index 5690859cf4b..f595be2cc5d 100644
--- a/src/fundamental/macro-fundamental.h
+++ b/src/fundamental/macro-fundamental.h
@@ -116,6 +116,12 @@
 #  define _retain_
 #endif
 
+#if HAVE_ATTRIBUTE_NO_REORDER
+#  define _no_reorder_ __attribute__((__no_reorder__))
+#else
+#  define _no_reorder_
+#endif
+
 #if __GNUC__ >= 15
 #  define _nonnull_if_nonzero_(p, n) __attribute__((nonnull_if_nonzero(p, n)))
 #else
diff --git a/src/shared/options.h b/src/shared/options.h
index afa17d9e300..c1ffa595ce8 100644
--- a/src/shared/options.h
+++ b/src/shared/options.h
@@ -25,6 +25,7 @@ typedef struct Option {
         _alignptr_                                                      \
         _used_                                                          \
         _retain_                                                        \
+        _no_reorder_                                                    \
         _variable_no_sanitize_address_                                  \
         static const Option CONCATENATE(option, counter) = {            \
                 .id = 0x100 + counter,                                  \
diff --git a/src/shared/verbs.h b/src/shared/verbs.h
index cd18359cd75..51a9e3a5253 100644
--- a/src/shared/verbs.h
+++ b/src/shared/verbs.h
@@ -26,6 +26,7 @@ typedef struct {
         _alignptr_                                                      \
         _used_                                                          \
         _retain_                                                        \
+        _no_reorder_                                                    \
         _variable_no_sanitize_address_                                  \
         static const Verb CONCATENATE(verb_data_, __COUNTER__) = {      \
                 .verb = v,                                              \