Hi!
If gcc is configured on aarch64-linux against new binutils, such as
2.46, it doesn't emit into assembly markings like
.section .note.gnu.property,"a"
.align 3
.word 4
.word 16
.word 5
.string "GNU"
.word 0xc0000000
.word 4
.word 0x7
.align 3
but instead emits
.aeabi_subsection aeabi_feature_and_bits, optional, ULEB128
.aeabi_attribute Tag_Feature_BTI, 1
.aeabi_attribute Tag_Feature_PAC, 1
.aeabi_attribute Tag_Feature_GCS, 1
The former goes into .note.gnu.propery section, the latter goes into
.ARM.attributes section.
Now, when linking without LTO or with LTO but without -g, all behaves
for the linked binaries the same, say for test.c
int main () {}
$ gcc -g -mbranch-protection=standard test.c -o test; readelf -j
.note.gnu.property test
Displaying notes found in: .note.gnu.property
Owner Data size Description
GNU 0x00000010 NT_GNU_PROPERTY_TYPE_0
Properties: AArch64 feature: BTI, PAC, GCS
$ gcc -flto -mbranch-protection=standard test.c -o test; readelf -j
.note.gnu.property test
Displaying notes found in: .note.gnu.property
Owner Data size Description
GNU 0x00000010 NT_GNU_PROPERTY_TYPE_0
Properties: AArch64 feature: BTI, PAC, GCS
$ gcc -flto -g -mbranch-protection=standard test.c -o test; readelf -j
.note.gnu.property test
readelf: Warning: Section '.note.gnu.property' was not dumped because it does
not exist
The problem is that the *.debug.temp.o object files created by lto-wrapper
don't have these markings. The function copies over .note.GNU-stack section
(so that it doesn't similarly on most arches break PT_GNU_STACK segment
flags), and .note.gnu.property (which used to hold this stuff e.g. on
aarch64 or x86, added in PR93966). But it doesn't copy the new
.ARM.attributes section.
The following patch fixes it by copying that section too. The function
unfortunately only works on names, doesn't know if it is copying ELF or some
other format (PE, Mach-O) or if it is copying ELF, whether it is EM_AARCH64
or some other arch. The following patch just copies the section always,
I think it is very unlikely people would use .ARM.attributes section for
some random unrelated stuff. If we'd want to limit it to just EM_AARCH64,
guess it would need to be done in
libiberty/simple-object-elf.c (simple_object_elf_copy_lto_debug_sections)
instead as an exception for the (*pfn) callback results (and there it could
e.g. verify SHT_AARCH64_ATTRIBUTES type but even there dunno if it has
access to the Ehdr stuff).
No testcase from me, dunno if e.g. the linker can flag the lack of those
during linking with some option rather than using readelf after link and
what kind of effective targets we'd need for such a test.
Bootstrapped/regtested on aarch64-linux, x86_64-linux and i686-linux,
and tested with the above mentioned test, it displays the notes even for
-flto -g now. Ok for trunk?
2026-03-05 Jakub Jelinek <[email protected]>
PR target/124365
* simple-object.c (handle_lto_debug_sections): Also copy over
.ARM.attributes section.
--- libiberty/simple-object.c.jj 2026-01-02 09:56:10.569329724 +0100
+++ libiberty/simple-object.c 2026-03-04 19:18:25.323807448 +0100
@@ -310,6 +310,10 @@ handle_lto_debug_sections (const char *n
/* Copy over .BTF section under the same name if present. */
else if (strcmp (name, ".BTF") == 0)
return strcpy (newname, name);
+ /* Copy over .ARM.attributes section under the same name if present. AArch64
+ aeabi attributes are present in this section. */
+ else if (strcmp (name, ".ARM.attributes") == 0)
+ return strcpy (newname, name);
free (newname);
return NULL;
}
Jakub
