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Index: head/libexec/rtld-elf/Symbol.map
===================================================================
--- head/libexec/rtld-elf/Symbol.map
+++ head/libexec/rtld-elf/Symbol.map
@@ -32,4 +32,6 @@
_rtld_get_stack_prot;
_rtld_is_dlopened;
_r_debug_postinit;
+ _rtld_version__FreeBSD_version;
+ _rtld_version_laddr_offset;
};
Index: head/libexec/rtld-elf/rtld.1
===================================================================
--- head/libexec/rtld-elf/rtld.1
+++ head/libexec/rtld-elf/rtld.1
@@ -355,6 +355,54 @@
and is naturally prone to race conditions.
Environments which rely on such restrictions are weak
and breakable on their own.
+.Sh VERSIONING
+Newer
+.Nm
+might provide some features or changes in runtime behavior that cannot be
+easily detected at runtime by checking of the normal exported symbols.
+Note that it is almost always wrong to verify
+.Dv __FreeBSD_version
+in userspace to detect features, either at compile or at run time,
+because either kernel, or libc, or environment variables could not
+match the running
+.Nm .
+.Pp
+To solve the problem,
+.Nm
+exports some feature indicators in the
+.Fx
+private symbols namespace
+.Dv FBSDprivate_1.0 .
+Symbols start with the
+.Dv _rtld_version
+prefix.
+Current list of defined symbols and corresponding features is:
+.Bl -tag -width indent
+.It Dv _rtld_version__FreeBSD_version
+Symbol exports the value of the
+.Dv __FreeBSD_version
+definition as it was provided during the
+.Nm
+build.
+The symbol is always present since the
+.Dv _rtld_version
+facility was introduced.
+.It Dv _rtld_version_laddr_offset
+The
+.Va l_addr
+member of the
+.Vt link_map
+structure contains the load offset of the shared object.
+Before that,
+.Va l_addr
+contained the base address of the library.
+See
+.Xr dlinfo 3 .
+.Pp
+Also it indicates the presence of
+.Va l_refname
+member of the structure.
+.El
.Sh FILES
.Bl -tag -width ".Pa /var/run/ld-elf32.so.hints" -compact
.It Pa /var/run/ld-elf.so.hints
@@ -369,6 +417,7 @@
.Sh SEE ALSO
.Xr ld 1 ,
.Xr ldd 1 ,
+.Xr dlinfo 3 ,
.Xr capsicum 4 ,
.Xr elf 5 ,
.Xr libmap.conf 5 ,
Index: head/libexec/rtld-elf/rtld.c
===================================================================
--- head/libexec/rtld-elf/rtld.c
+++ head/libexec/rtld-elf/rtld.c
@@ -5785,3 +5785,9 @@
return (__crt_realloc(cp, nbytes));
}
+
+extern int _rtld_version__FreeBSD_version __exported;
+int _rtld_version__FreeBSD_version = __FreeBSD_version;
+
+extern char _rtld_version_laddr_offset __exported;
+char _rtld_version_laddr_offset;

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