[PATCH v2 1/5] ld: fix segfault caused by untagged stub sections
Matthieu Longo
matthieu.longo@arm.com
Tue Oct 14 10:46:07 GMT 2025
In the case of non-contiguous memory regions, a far-call stub section
must be assigned to the memory of the section it was originally emitted
for. If the stub section does not fit, the section is marked as dropped,
and removed later. To emit a useful message to the user, however, a stub
section needs to be discernible from sections originating from input
objects.
Previously [1], this distinction was made using the SEC_LINKER_CREATED
flag only in the AArch32 backend handler <arch>_add_stub_section. Other
backends that didn't set this flag on their stub sections skipped required
checks in ld/ldlang.c:size_input_section(). On AArch64, this caused the
linker to proceed into code paths that assumed output sections were set,
instead of reporting fatal errors, and ultimately led to a segmentation
fault.
However, the SEC_LINKER_CREATED flag does not solely indicate that a
section was created by the linker. Its original meaning also meant that
the section should not be handled by the generic relocation code. Reusing
this flag to identify stub sections, while it appeared to fix the issue,
introduced unintended side effects. On PowerPC, for instance, it skipped
relocations present in the stubs and interpreted them as absolute
addresses.
This patch proposes a new attribute 'veneer', indicating that a section
contains branch veneers. The attribute is set on AArch32, AArch64 and
PowerPC immediately after the creation of the stub section. Others
architectures are left unchanged, as they do not appear to support
non-contiguous memory regions (no tests were found to verify the fix).
Additionally, the diagnostic message was improved when a stub cannot be
placed in the same memory region as its referencing code.
[1]: abf874a, Add support for non-contiguous memory regions.
---
bfd/bfd-in2.h | 6 ++++++
bfd/libbfd.h | 3 +++
bfd/section.c | 9 +++++++++
ld/emultempl/aarch64elf.em | 2 ++
ld/emultempl/armelf.em | 5 +++--
ld/emultempl/ppc64elf.em | 2 ++
ld/ldlang.c | 13 +++++++------
ld/testsuite/ld-arm/non-contiguous-arm4.d | 2 +-
ld/testsuite/ld-powerpc/non-contiguous-powerpc64.d | 2 +-
9 files changed, 34 insertions(+), 10 deletions(-)
diff --git a/bfd/bfd-in2.h b/bfd/bfd-in2.h
index 5e7c6ddf1ee..6d0c574c601 100644
--- a/bfd/bfd-in2.h
+++ b/bfd/bfd-in2.h
@@ -702,6 +702,12 @@ typedef struct bfd_section
/* Nonzero if section contents should not be freed. */
unsigned int alloced:1;
+ /* Indicate that the section contains branch veneers. This is used when
+ support for non-contiguous memory regions is enabled. The veneers have
+ to be allocated to the same memory region as the code they are refered
+ by, i.e. they cannot be moved to a subsequent memory region. */
+ unsigned int veneer : 1;
+
/* Bits used by various backends. The generic code doesn't touch
these fields. */
diff --git a/bfd/libbfd.h b/bfd/libbfd.h
index f2485d99078..5e2bfdb7c61 100644
--- a/bfd/libbfd.h
+++ b/bfd/libbfd.h
@@ -3670,6 +3670,9 @@ bool _bfd_unrecognized_reloc
/* segment_mark, sec_info_type, use_rela_p, mmapped_p, alloced, */ \
0, 0, 0, 0, 0, \
\
+ /* veneer, */ \
+ 0, \
+ \
/* sec_flg0, sec_flg1, sec_flg2, sec_flg3, sec_flg4, sec_flg5, */ \
0, 0, 0, 0, 0, 0, \
\
diff --git a/bfd/section.c b/bfd/section.c
index 5f0cf6e71cb..9356d1a30f7 100644
--- a/bfd/section.c
+++ b/bfd/section.c
@@ -428,6 +428,12 @@ CODE_FRAGMENT
. {* Nonzero if section contents should not be freed. *}
. unsigned int alloced:1;
.
+. {* Indicate that the section contains branch veneers. This is used when
+. support for non-contiguous memory regions is enabled. The veneers have
+. to be allocated to the same memory region as the code they are refered
+. by, i.e. they cannot be moved to a subsequent memory region. *}
+. unsigned int veneer : 1;
+.
. {* Bits used by various backends. The generic code doesn't touch
. these fields. *}
.
@@ -723,6 +729,9 @@ INTERNAL
. {* segment_mark, sec_info_type, use_rela_p, mmapped_p, alloced, *} \
. 0, 0, 0, 0, 0, \
. \
+. {* veneer, *} \
+. 0, \
+. \
. {* sec_flg0, sec_flg1, sec_flg2, sec_flg3, sec_flg4, sec_flg5, *} \
. 0, 0, 0, 0, 0, 0, \
. \
diff --git a/ld/emultempl/aarch64elf.em b/ld/emultempl/aarch64elf.em
index 91d58d8fe5a..353d6b53425 100644
--- a/ld/emultempl/aarch64elf.em
+++ b/ld/emultempl/aarch64elf.em
@@ -200,6 +200,8 @@ elf${ELFSIZE}_aarch64_add_stub_section (const char *stub_sec_name,
if (stub_sec == NULL)
goto err_ret;
+ stub_sec->veneer = 1;
+
/* Long branch stubs contain a 64-bit address, so the section requires
8 byte alignment. */
bfd_set_section_alignment (stub_sec, 3);
diff --git a/ld/emultempl/armelf.em b/ld/emultempl/armelf.em
index 6f652c59a3c..04c8cbd323c 100644
--- a/ld/emultempl/armelf.em
+++ b/ld/emultempl/armelf.em
@@ -237,13 +237,14 @@ elf32_arm_add_stub_section (const char * stub_sec_name,
struct hook_stub_info info;
flags = (SEC_ALLOC | SEC_LOAD | SEC_READONLY | SEC_CODE
- | SEC_HAS_CONTENTS | SEC_RELOC | SEC_IN_MEMORY | SEC_KEEP
- | SEC_LINKER_CREATED);
+ | SEC_HAS_CONTENTS | SEC_RELOC | SEC_IN_MEMORY | SEC_KEEP);
stub_sec = bfd_make_section_anyway_with_flags (stub_file->the_bfd,
stub_sec_name, flags);
if (stub_sec == NULL)
goto err_ret;
+ stub_sec->veneer = 1;
+
bfd_set_section_alignment (stub_sec, alignment_power);
os = lang_output_section_get (output_section);
diff --git a/ld/emultempl/ppc64elf.em b/ld/emultempl/ppc64elf.em
index 857cf54ad06..5291a8c704a 100644
--- a/ld/emultempl/ppc64elf.em
+++ b/ld/emultempl/ppc64elf.em
@@ -440,6 +440,8 @@ ppc_add_stub_section (const char *stub_sec_name, asection *input_section)
: 5)))
goto err_ret;
+ stub_sec->veneer = 1;
+
output_section = input_section->output_section;
os = lang_output_section_get (output_section);
diff --git a/ld/ldlang.c b/ld/ldlang.c
index 3c57bf7541c..bdda599a7a4 100644
--- a/ld/ldlang.c
+++ b/ld/ldlang.c
@@ -5637,10 +5637,12 @@ size_input_section
if (dot + TO_ADDR (i->size) > end)
{
- if (i->flags & SEC_LINKER_CREATED)
- fatal (_("%P: Output section `%pA' not large enough for "
- "the linker-created stubs section `%pA'.\n"),
- i->output_section, i);
+ if (i->veneer)
+ fatal (_("%P: Memory region `%s' not large enough for the "
+ "linker-created stubs section `%pA' associated to "
+ "output section `%pA'\n"),
+ output_section_statement->region->name_list.name, i,
+ i->output_section);
if (i->rawsize && i->rawsize != i->size)
fatal (_("%P: Relaxation not supported with "
@@ -8239,8 +8241,7 @@ warn_non_contiguous_discards (void)
continue;
for (asection *s = file->the_bfd->sections; s != NULL; s = s->next)
- if (s->output_section == NULL
- && (s->flags & SEC_LINKER_CREATED) == 0)
+ if (s->output_section == NULL && !s->veneer)
einfo (_("%P: warning: --enable-non-contiguous-regions "
"discards section `%pA' from `%pB'\n"),
s, file->the_bfd);
diff --git a/ld/testsuite/ld-arm/non-contiguous-arm4.d b/ld/testsuite/ld-arm/non-contiguous-arm4.d
index a8e9d66caca..d4c4b284dce 100644
--- a/ld/testsuite/ld-arm/non-contiguous-arm4.d
+++ b/ld/testsuite/ld-arm/non-contiguous-arm4.d
@@ -1,4 +1,4 @@
#name: non-contiguous-arm4
#source: non-contiguous-arm.s
#ld: --enable-non-contiguous-regions -T non-contiguous-arm4.ld
-# error: .*Output section .?\.ramu.? not large enough for the linker-created stubs section .?\.code\.3\.__stub.\.?
+# error: Memory region `RAMU' not large enough for the linker-created stubs section `\.code\.3\.__stub' associated to output section `\.ramu'
diff --git a/ld/testsuite/ld-powerpc/non-contiguous-powerpc64.d b/ld/testsuite/ld-powerpc/non-contiguous-powerpc64.d
index 9f903bbea35..1a7e4c5a23b 100644
--- a/ld/testsuite/ld-powerpc/non-contiguous-powerpc64.d
+++ b/ld/testsuite/ld-powerpc/non-contiguous-powerpc64.d
@@ -2,4 +2,4 @@
#source: non-contiguous-powerpc.s
#as: -a64
#ld: -melf64ppc --enable-non-contiguous-regions -T non-contiguous-powerpc.ld
-#error: .*Could not assign .?\.text\.one\.stub.? to an output section\. Retry without --enable-non-contiguous-regions\.
+#error: Memory region `one' not large enough for the linker-created stubs section `\.text\.one\.stub' associated to output section `one'
--
2.51.0
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