Fix: symbols eliminated by --gc-sections still trigger warnings for gnu.warning.SYM

  PR 31067
  * linker.c (_bfd_generic_link_add_one_symbol): When issuing a warning message, also display a message about the warning not being affected by garbage colleciton.
  * ld.texi (Special Sections): New entry in the linker manual. Describes how the .gnu.warning and .gnu.warning.SYM sections behave.

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 143069894c169e2262f2b695aedecbb381d95851..e9f571acac26690cf5a4216cb4fed3223340dd6e 100644 (file)
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,10 @@
+2023-11-21  Nick Clifton  <nickc@redhat.com>
+
+       PR 31067
+       linker.c (_bfd_generic_link_add_one_symbol): When issuing a
+       warning message, also display a message about the warning not
+       being affected by garbage colleciton.
+
 2023-11-15  Arsen Arsenović  <arsen@aarsen.me>
 
        * aclocal.m4: Regenerate.

diff --git a/bfd/linker.c b/bfd/linker.c
index 28fffc3ad6319ebb5fd1856e2c0507d028ba742d..90dc581cfe3242145c120d324e54963c3e494fe1 100644 (file)
--- a/bfd/linker.c
+++ b/bfd/linker.c
@@ -1784,6 +1784,14 @@ _bfd_generic_link_add_one_symbol (struct bfd_link_info *info,
            {
              (*info->callbacks->warning) (info, string, h->root.string,
                                           hash_entry_bfd (h), NULL, 0);
+             /* PR 31067: If garbage collection is enabled then the
+                referenced symbol may actually be discarded later on.
+                This could be very confusing to the user.  So give them
+                a hint as to what might be happening.  */
+             if (info->gc_sections)
+               (*info->callbacks->info)
+                 (_("%P: %pB: note: the message above does not take linker garbage collection into account\n"),
+                  hash_entry_bfd (h));
              break;
            }
          /* Fall through.  */

diff --git a/ld/ChangeLog b/ld/ChangeLog
index a30d3ad39b606817938e0c8a85a1e9303dcb1e2d..1766bd86dc2f1d0d231212abbb28479603841f41 100644 (file)
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,10 @@
+2023-11-21  Nick Clifton  <nickc@redhat.com>
+
+       PR 31067
+       * ld.texi (Special Sections): New entry in the linker manual.
+       Describes how the .gnu.warning and .gnu.warning.SYM sections
+       behave.
+
 2023-11-15  Arsen Arsenović  <arsen@aarsen.me>
 
        * aclocal.m4: Regenerate.

diff --git a/ld/ld.texi b/ld/ld.texi
index 5a143b2b5186d2892b2892f90c5bd1bcaf446a00..0704eece8d667a3f8cc0c828bfed7ee6c3139860 100644 (file)
--- a/ld/ld.texi
+++ b/ld/ld.texi
@@ -127,6 +127,7 @@ in the section entitled ``GNU Free Documentation License''.
 * Invocation::                  Invocation
 * Scripts::                     Linker Scripts
 * Plugins::                     Linker Plugins
+* Special Sections::            Special Sections
 @ifset GENERIC
 * Machine Dependent::           Machine Dependent Features
 @end ifset
@@ -7525,6 +7526,50 @@ the @samp{__.LIBDEP} member of @file{libssl.a} would contain
 -L/usr/local/lib -lcrypto
 @end smallexample
 
+@node Special Sections
+When linking ELF format object files @command{ld} treats some sections
+in a special, non standard manner.  This part of the manual describes
+these sections.
+
+@table @gcctabopt
+@item .gnu.warning
+The contents of any section with this name are assumed to be an ascii
+format warning message.  The contents will be displayed to the user if
+the sections appears in any input file, but the section will not be
+copied into the output image.  If the @option{--fatal-warnings} option
+is enabled then the warnings - if any are encountered - will also stop
+the link from completing.
+
+Note - the @samp{.gnu.warning} section is not subject to linker
+garbage collection or orphan handling.
+
+@item .gnu.warning.@var{SYM}
+The contents of any section whoes name starts with the prefix
+@samp{.gnu.warning.} and then finishes with the name of a symbol is
+treated in a similar fashion to the @samp{.gnu.warning} section, but
+only if the named symbol is defined.  So for example the contents of a
+section called @samp{.gnu.warning.foo} will be displayed as warning
+message if, and only if, the symbol @samp{foo} is defined by one or
+more of the input files.  This includes object files pulled in from
+static libraries, shared objects needed to complete the link and so
+on.
+
+Note - because these warning messages are generated before the linker
+performs garbage collection (if enabled) it is possible for a warning
+to be displayed for a symbol that is later removed and then never
+appears in the final output.
+
+@item .note.gnu.property
+When the linker combines sections of this name it will merge them
+together according to various rules encoded into the notes
+themselves.  Therefore the contents of the output .note.gnu.property
+section may not correspond to a simple concatenation of the input
+sections.  If the @option{-Map} option has been used to request a
+linker map then details of any property merging will be included in
+the map.
+
+@end table
+
 @ifset GENERIC
 @node Machine Dependent
 @chapter Machine Dependent Features