* [PATCH v3 1/2] aarch64: Fix DT_RELR support with discarded sections
2024-06-06 10:52 [PATCH v3 0/2] aarch64: fix DT_RELR with discarded sections Szabolcs Nagy
@ 2024-06-06 10:53 ` Szabolcs Nagy
2024-06-06 10:53 ` [PATCH v3 2/2] aarch64: Test DT_RELR " Szabolcs Nagy
2024-06-07 2:20 ` [PATCH v3 0/2] aarch64: fix " Alan Modra
2 siblings, 0 replies; 4+ messages in thread
From: Szabolcs Nagy @ 2024-06-06 10:53 UTC (permalink / raw)
To: binutils
In case of discarded sections, via /DISCARD/ or .gnu.linkonce,
relr relocation accounting was wrong. This broke building linux.
The issue was that the *_relocate_section logic was copied to
record_relr_non_got_relocs to find the relative relocs that can
be packed, however *_relocate_section is not called on sections
that are discarded, while record_relr_non_got_relocs is called
for all input sections. The fix is to filter out the discarded
sections with the same logic that is used to count non-GOT
relocs in *_late_size_sections for local symbols earlier.
Use the discarded_section helper in both cases to clarify the
intent and handle all corner-cases consistently.
GOT relocations are affected too if all sections are discarded
that reference the GOT entry of a particular symbol, however
this can cause unused GOT entries independently of DT_RELR, and
the only difference with DT_RELR is that a relative reloc may be
emitted instead of a R_AARCH64_NONE for the unused GOT entry
which is acceptable. A proper fix would require redoing the GOT
refcounting after we know the discarded sections, see bug 31850.
---
v3:
- use discarded_section()
- adjust commit msg
v2:
- only commit msg update: i realized that the GOT case is not
handled right when DT_RELR is disabled so there is no point
trying to fix that here and unnecessary relative relocation
in such corner-case is acceptable. i updated the test case
patch to cover the GOT cases that currently work.
---
bfd/elfnn-aarch64.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/bfd/elfnn-aarch64.c b/bfd/elfnn-aarch64.c
index 81f1a646125..2221de0a480 100644
--- a/bfd/elfnn-aarch64.c
+++ b/bfd/elfnn-aarch64.c
@@ -9327,6 +9327,8 @@ record_relr_non_got_relocs (bfd *input_bfd, struct bfd_link_info *info,
return true;
if (sec->alignment_power == 0)
return true;
+ if (discarded_section (sec))
+ return true;
sreloc = elf_section_data (sec)->sreloc;
if (sreloc == NULL)
return true;
@@ -9602,8 +9604,7 @@ elfNN_aarch64_late_size_sections (bfd *output_bfd ATTRIBUTE_UNUSED,
for (p = (struct elf_dyn_relocs *)
(elf_section_data (s)->local_dynrel); p != NULL; p = p->next)
{
- if (!bfd_is_abs_section (p->sec)
- && bfd_is_abs_section (p->sec->output_section))
+ if (discarded_section (p->sec))
{
/* Input section has been discarded, either because
it is a copy of a linkonce section or due to
--
2.25.1
^ permalink raw reply [flat|nested] 4+ messages in thread* [PATCH v3 2/2] aarch64: Test DT_RELR with discarded sections
2024-06-06 10:52 [PATCH v3 0/2] aarch64: fix DT_RELR with discarded sections Szabolcs Nagy
2024-06-06 10:53 ` [PATCH v3 1/2] aarch64: Fix DT_RELR support " Szabolcs Nagy
@ 2024-06-06 10:53 ` Szabolcs Nagy
2024-06-07 2:20 ` [PATCH v3 0/2] aarch64: fix " Alan Modra
2 siblings, 0 replies; 4+ messages in thread
From: Szabolcs Nagy @ 2024-06-06 10:53 UTC (permalink / raw)
To: binutils
---
v3:
- add comment about bug.
---
ld/testsuite/ld-aarch64/aarch64-elf.exp | 2 +
ld/testsuite/ld-aarch64/relr-discard-pie.d | 18 ++++++
ld/testsuite/ld-aarch64/relr-discard-shared.d | 18 ++++++
ld/testsuite/ld-aarch64/relr-discard.ld | 13 ++++
ld/testsuite/ld-aarch64/relr-discard.s | 63 +++++++++++++++++++
5 files changed, 114 insertions(+)
create mode 100644 ld/testsuite/ld-aarch64/relr-discard-pie.d
create mode 100644 ld/testsuite/ld-aarch64/relr-discard-shared.d
create mode 100644 ld/testsuite/ld-aarch64/relr-discard.ld
create mode 100644 ld/testsuite/ld-aarch64/relr-discard.s
diff --git a/ld/testsuite/ld-aarch64/aarch64-elf.exp b/ld/testsuite/ld-aarch64/aarch64-elf.exp
index 38929ffc3c6..0e70ca3e028 100644
--- a/ld/testsuite/ld-aarch64/aarch64-elf.exp
+++ b/ld/testsuite/ld-aarch64/aarch64-elf.exp
@@ -475,6 +475,8 @@ run_dump_test_lp64 "relr-got-pie"
run_dump_test_lp64 "relr-got-shared"
run_dump_test_lp64 "relr-text-pie"
run_dump_test_lp64 "relr-text-shared"
+run_dump_test_lp64 "relr-discard-pie"
+run_dump_test_lp64 "relr-discard-shared"
if { ![skip_sframe_tests] } {
run_dump_test "sframe-simple-1"
diff --git a/ld/testsuite/ld-aarch64/relr-discard-pie.d b/ld/testsuite/ld-aarch64/relr-discard-pie.d
new file mode 100644
index 00000000000..7e7f341bc36
--- /dev/null
+++ b/ld/testsuite/ld-aarch64/relr-discard-pie.d
@@ -0,0 +1,18 @@
+#source: relr-discard.s
+#ld: -pie --no-apply-dynamic-relocs -z pack-relative-relocs -T relr-discard.ld
+#readelf: -rW
+
+# Note: There are unnecessary GOT entries and *_NONE relocations
+# for those GOT entries and discarded locations, this is bug 31850.
+
+Relocation section '\.rela\.dyn' at offset 0x1.* contains 4 entries:
+ Offset Info Type Symbol's Value Symbol's Name \+ Addend
+0000000000000000 0000000000000000 R_AARCH64_NONE 0
+0000000000000000 0000000000000000 R_AARCH64_NONE 0
+0000000000000000 0000000000000000 R_AARCH64_NONE 0
+0000000000000000 0000000000000000 R_AARCH64_NONE 0
+
+Relocation section '\.relr\.dyn' at offset 0x1.* contains 2 entries which relocate 2 locations:
+Index: Entry Address Symbolic Address
+0000: 0000000000020008 0000000000020008 _GLOBAL_OFFSET_TABLE_ \+ 0x8
+0001: 0000000000000003 0000000000020010 _GLOBAL_OFFSET_TABLE_ \+ 0x10
diff --git a/ld/testsuite/ld-aarch64/relr-discard-shared.d b/ld/testsuite/ld-aarch64/relr-discard-shared.d
new file mode 100644
index 00000000000..9260a6d69c4
--- /dev/null
+++ b/ld/testsuite/ld-aarch64/relr-discard-shared.d
@@ -0,0 +1,18 @@
+#source: relr-discard.s
+#ld: -shared --no-apply-dynamic-relocs -z pack-relative-relocs -T relr-discard.ld
+#readelf: -rW
+
+# Note: There are unnecessary GOT entries and *_NONE relocations
+# for those GOT entries and discarded locations, this is bug 31850.
+
+Relocation section '\.rela\.dyn' at offset 0x1.* contains 5 entries:
+ Offset Info Type Symbol's Value Symbol's Name \+ Addend
+0000000000000000 0000000000000000 R_AARCH64_NONE 0
+0000000000000000 0000000000000000 R_AARCH64_NONE 0
+0000000000000000 0000000000000000 R_AARCH64_NONE 0
+0000000000000000 0000000000000000 R_AARCH64_NONE 0
+0000000000020010 .* R_AARCH64_GLOB_DAT 000000000001000c sym_global \+ 0
+
+Relocation section '\.relr\.dyn' at offset 0x1.* contains 1 entry which relocates 1 location:
+Index: Entry Address Symbolic Address
+0000: 0000000000020008 0000000000020008 _GLOBAL_OFFSET_TABLE_ \+ 0x8
diff --git a/ld/testsuite/ld-aarch64/relr-discard.ld b/ld/testsuite/ld-aarch64/relr-discard.ld
new file mode 100644
index 00000000000..288ba23e11c
--- /dev/null
+++ b/ld/testsuite/ld-aarch64/relr-discard.ld
@@ -0,0 +1,13 @@
+OUTPUT_ARCH(aarch64)
+ENTRY(_start)
+SECTIONS
+{
+ /DISCARD/ : { *(.discard.*) }
+
+ . = 0x10000;
+ .text : { *(.text) }
+ . = 0x20000;
+ .got : { *(.got) *(.got.plt)}
+ . = 0x30000;
+ .data : { *(.data) *(.data.*) }
+}
diff --git a/ld/testsuite/ld-aarch64/relr-discard.s b/ld/testsuite/ld-aarch64/relr-discard.s
new file mode 100644
index 00000000000..0ed9b4a9098
--- /dev/null
+++ b/ld/testsuite/ld-aarch64/relr-discard.s
@@ -0,0 +1,63 @@
+// Test DT_RELR with references in discarded sections.
+
+.text
+.p2align 3
+.global _start
+_start:
+ nop
+
+sym_local:
+ nop
+
+.global sym_hidden
+.hidden sym_hidden
+sym_hidden:
+ nop
+
+.global sym_global
+sym_global:
+ nop
+
+.global sym_global_abs
+.set sym_global_abs, 42
+
+.global sym_weak_undef
+.weak sym_weak_undef
+
+.section .discard.got_local,"ax"
+ adrp x0, :got:sym_local
+ ldr x0, [x0, :got_lo12:sym_local]
+
+.section .discard.got_global,"ax"
+ adrp x0, :got:sym_global
+ ldr x0, [x0, :got_lo12:sym_global]
+
+.section .discard.local,"a"
+.p2align 1
+discard_local:
+.xword sym_local
+
+.section .discard.hidden,"a"
+.p2align 1
+discard_hidden:
+.xword sym_hidden
+
+.section .discard.global,"a"
+.p2align 1
+discard_global:
+.xword sym_global
+
+.section .discard.global_abs,"a"
+.p2align 1
+discard_global_abs:
+.xword sym_global_abs
+
+.section .discard.weak_undef,"a"
+.p2align 1
+discard_weak_undef:
+.xword sym_weak_undef
+
+.section .discard._DYNAMIC,"a"
+.p2align 1
+discard_DYNAMIC:
+.xword _DYNAMIC
--
2.25.1
^ permalink raw reply [flat|nested] 4+ messages in thread