[PATCH v1 1/1] ld: microblaze: don't index the local symbol cache with a global symbol index

From: Sam Price <[email protected]>

microblaze_elf_relax_section() was copied from sh_elf_relax_delete_bytes()
in 2009 (7ba29e2a41) but the copy dropped a bounds check that was already
present in the sh original.  This adds the missing two-line guard from
bfd/elf32-sh.c:1227-1228, preventing an out-of-bounds read that silently
corrupts relocation addends.

The bug: when scanning relocations in other sections, the code indexes
isymbuf with a global symbol index without checking it against sh_info.
isymbuf (from symtab_hdr->contents) holds only sh_info local symbols, so
global symbol indices read past the end of the allocation.

If the out-of-bounds bytes happen to look like a local section symbol for
the section being relaxed, the relocation's addend is incorrectly adjusted,
losing 4 bytes per deleted IMM instruction.  This corrupts structure member
accesses built at -O2:

	lwi rD, r0, sym + offsetof(struct s, member)

This was found as a silent miscompilation in RTEMS where
Per_CPU_Control::executing was fetched as Per_CPU_Control::dispatch_necessary.

The fix copies the guard from bfd/elf32-sh.c:1227-1228, present since the
first binutils commit (252b5132c7, 1999-05-03).

Three tests are added (the first for this target), checking that addends
survive relaxation.  relax-addend.d and relax-addend-data.d use
--gc-sections; relax-addend-eh.d uses .eh_frame editing (the route live on
current master).

Test behavior depends on how ld was built:

  ld built normally   all three pass with and without the fix, because
                      whether the out-of-bounds read corrupts the addend
                      depends on what is in the adjacent heap

  ld built with ASan  relax-addend-eh.d FAILS without the fix, because the
                      read itself is unconditional and ASan traps it, and
                      passes with the fix

ld/testsuite results on microblaze-elf are otherwise unchanged.

bfd/
	* elf32-microblaze.c (microblaze_elf_relax_section): Skip
	relocations against global symbols when scanning the relocations
	of other sections.

ld/
	* testsuite/ld-microblaze/microblaze.exp: New file.
	* testsuite/ld-microblaze/relax-addend.s: New file.
	* testsuite/ld-microblaze/relax-addend-support.s: New file.
	* testsuite/ld-microblaze/relax-addend.ld: New file.
	* testsuite/ld-microblaze/relax-addend.d: New test.
	* testsuite/ld-microblaze/relax-addend-data.d: New test.
	* testsuite/ld-microblaze/relax-addend-eh.s: New file.
	* testsuite/ld-microblaze/relax-addend-eh-support.s: New file.
	* testsuite/ld-microblaze/relax-addend-eh.ld: New file.
	* testsuite/ld-microblaze/relax-addend-eh.d: New test.

Signed-off-by: Neal Frager <[email protected]>
Signed-off-by: Sam Price <[email protected]>
Assisted-by: Claude (Anthropic)
---
 bfd/elf32-microblaze.c                        |  3 +
 ld/testsuite/ld-microblaze/microblaze.exp     | 28 +++++++
 .../ld-microblaze/relax-addend-data.d         | 17 +++++
 .../ld-microblaze/relax-addend-eh-support.s   | 16 ++++
 ld/testsuite/ld-microblaze/relax-addend-eh.d  | 27 +++++++
 ld/testsuite/ld-microblaze/relax-addend-eh.ld |  9 +++
 ld/testsuite/ld-microblaze/relax-addend-eh.s  | 76 +++++++++++++++++++
 .../ld-microblaze/relax-addend-support.s      | 24 ++++++
 ld/testsuite/ld-microblaze/relax-addend.d     | 26 +++++++
 ld/testsuite/ld-microblaze/relax-addend.ld    | 23 ++++++
 ld/testsuite/ld-microblaze/relax-addend.s     | 55 ++++++++++++++
 11 files changed, 304 insertions(+)
 create mode 100644 ld/testsuite/ld-microblaze/microblaze.exp
 create mode 100644 ld/testsuite/ld-microblaze/relax-addend-data.d
 create mode 100644 ld/testsuite/ld-microblaze/relax-addend-eh-support.s
 create mode 100644 ld/testsuite/ld-microblaze/relax-addend-eh.d
 create mode 100644 ld/testsuite/ld-microblaze/relax-addend-eh.ld
 create mode 100644 ld/testsuite/ld-microblaze/relax-addend-eh.s
 create mode 100644 ld/testsuite/ld-microblaze/relax-addend-support.s
 create mode 100644 ld/testsuite/ld-microblaze/relax-addend.d
 create mode 100644 ld/testsuite/ld-microblaze/relax-addend.ld
 create mode 100644 ld/testsuite/ld-microblaze/relax-addend.s

diff --git a/bfd/elf32-microblaze.c b/bfd/elf32-microblaze.c
index a52358a9a12..06cfb42cd6f 100644
--- a/bfd/elf32-microblaze.c
+++ b/bfd/elf32-microblaze.c
@@ -2084,6 +2084,9 @@ microblaze_elf_relax_section (bfd *abfd,
 	  irelscanend = irelocs + o->reloc_count;
 	  for (irelscan = irelocs; irelscan < irelscanend; irelscan++)
 	    {
+	      if (ELF32_R_SYM (irelscan->r_info) >= symtab_hdr->sh_info)
+		continue;
+
 	      if ((ELF32_R_TYPE (irelscan->r_info) == (int) R_MICROBLAZE_32)
 		  || (ELF32_R_TYPE (irelscan->r_info) == (int) R_MICROBLAZE_32_NONE))
 		{
diff --git a/ld/testsuite/ld-microblaze/microblaze.exp b/ld/testsuite/ld-microblaze/microblaze.exp
new file mode 100644
index 00000000000..919fc2c2a49
--- /dev/null
+++ b/ld/testsuite/ld-microblaze/microblaze.exp
@@ -0,0 +1,28 @@
+# Expect script for MicroBlaze ELF linker tests.
+#   Copyright (C) 2026 Free Software Foundation, Inc.
+#
+# This file is part of the GNU Binutils.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
+# MA 02110-1301, USA.
+
+if { ![istarget "microblaze*-*-*"] } {
+    return
+}
+
+foreach test [lsort [glob -nocomplain $srcdir/$subdir/*.d]] {
+    verbose [file rootname $test]
+    run_dump_test [file rootname $test]
+}
diff --git a/ld/testsuite/ld-microblaze/relax-addend-data.d b/ld/testsuite/ld-microblaze/relax-addend-data.d
new file mode 100644
index 00000000000..c4b5232d870
--- /dev/null
+++ b/ld/testsuite/ld-microblaze/relax-addend-data.d
@@ -0,0 +1,17 @@
+#source: relax-addend.s
+#source: relax-addend-support.s
+#as: -EL
+#ld: -EL -relax --gc-sections -T $srcdir/$subdir/relax-addend.ld
+#readelf: -x .checkdata
+#name: MicroBlaze relaxation preserves R_MICROBLAZE_32 addends
+
+# The same check for the R_MICROBLAZE_32 arm of the same loop, using a data
+# word rather than an instruction so that readelf alone can verify it.
+# .checkdata holds a single word initialised to gvar + 0x18; with .data pinned
+# by the linker script that is 0x90001018, little endian 18 10 00 90.
+# A linker which corrupts the addend stores 14 10 00 90.
+
+#...
+Hex dump of section '.checkdata':
+[ 	]*0x90001100 18100090 .*
+#pass
diff --git a/ld/testsuite/ld-microblaze/relax-addend-eh-support.s b/ld/testsuite/ld-microblaze/relax-addend-eh-support.s
new file mode 100644
index 00000000000..d06df4b83e8
--- /dev/null
+++ b/ld/testsuite/ld-microblaze/relax-addend-eh-support.s
@@ -0,0 +1,16 @@
+	.section .text.zz_support,"ax",@progbits
+	.globl	near_callee
+near_callee:
+	rtsd	r15, 8
+	nop
+	.globl	_start
+_start:
+	brlid	r15, aaa_relaxed
+	nop
+	brlid	r15, zzz_victim
+	nop
+	bri	0
+	.data
+	.globl	gvar
+	.align	2
+gvar:	.space	64
diff --git a/ld/testsuite/ld-microblaze/relax-addend-eh.d b/ld/testsuite/ld-microblaze/relax-addend-eh.d
new file mode 100644
index 00000000000..d061fd04fb1
--- /dev/null
+++ b/ld/testsuite/ld-microblaze/relax-addend-eh.d
@@ -0,0 +1,27 @@
+#source: relax-addend-eh.s
+#source: relax-addend-eh-support.s
+#as: -EL
+#ld: -EL -relax --gc-sections -T $srcdir/$subdir/relax-addend-eh.ld
+#objdump: -d
+#name: MicroBlaze relaxation preserves addends across .eh_frame editing
+
+# Same defect as relax-addend.d, reached the other way.
+#
+# _bfd_elf_discard_section_eh_frame installs a locals-only symbol cache in
+# symtab_hdr->contents when editing .eh_frame moves a local symbol defined
+# inside it; the generic ELF emulation then calls lang_relax_sections from the
+# same after_allocation.  dead_fn is unreferenced, so --gc-sections drops it,
+# its FDE is removed, the section shrinks and ehlocal moves -- which is what
+# makes the cache appear.  The linker script must KEEP .eh_frame or it is swept
+# and none of this happens.
+#
+# gvar lands at 0x90000074, so the reference to gvar + 0x18 must be 0x9000008c,
+# encoded as IMM 0x9000 followed by LWI with 0x008c.  A linker which corrupts
+# the addend emits e8600088.
+
+.*: +file format .*
+#...
+9000001c <zzz_victim>:
+[ 	]*9000001c:[ 	]+b0009000[ 	]+imm[ 	]+-28672
+[ 	]*90000020:[ 	]+e860008c[ 	]+lwi[ 	]+r3, r0, 140
+#pass
diff --git a/ld/testsuite/ld-microblaze/relax-addend-eh.ld b/ld/testsuite/ld-microblaze/relax-addend-eh.ld
new file mode 100644
index 00000000000..c0d11cc9cb4
--- /dev/null
+++ b/ld/testsuite/ld-microblaze/relax-addend-eh.ld
@@ -0,0 +1,9 @@
+ENTRY(_start)
+SECTIONS
+{
+  . = 0x90000000;
+  .text : { *(.text) *(.text.*) }
+  .eh_frame : { KEEP (*(.eh_frame)) }
+  .data : { *(.data) *(.data.*) }
+  /DISCARD/ : { *(.comment) *(.note*) }
+}
diff --git a/ld/testsuite/ld-microblaze/relax-addend-eh.s b/ld/testsuite/ld-microblaze/relax-addend-eh.s
new file mode 100644
index 00000000000..5900f8cc956
--- /dev/null
+++ b/ld/testsuite/ld-microblaze/relax-addend-eh.s
@@ -0,0 +1,76 @@
+/* dead_fn is dropped by --gc-sections; its FDE is then removed from .eh_frame,
+   which shifts ehlocal and makes adjust_eh_frame_local_symbols() cache a
+   locals-only symbol buffer in symtab_hdr->contents. */
+	.section .text.dead,"ax",@progbits
+	.globl	dead_fn
+	.type	dead_fn,@function
+dead_fn:
+	rtsd	r15, 8
+	nop
+	.size	dead_fn, .-dead_fn
+
+	.section .text.aaa_relaxed,"ax",@progbits
+	.globl	aaa_relaxed
+	.type	aaa_relaxed,@function
+aaa_relaxed:
+	addik	r1, r1, -28
+	swi	r15, r1, 0
+	brlid	r15, near_callee
+	nop
+	lwi	r15, r1, 0
+	rtsd	r15, 8
+	addik	r1, r1, 28
+	.size	aaa_relaxed, .-aaa_relaxed
+
+	.section .text.zzz_victim,"ax",@progbits
+	.globl	zzz_victim
+	.type	zzz_victim,@function
+zzz_victim:
+	lwi	r3, r0, gvar+24
+	rtsd	r15, 8
+	nop
+	.size	zzz_victim, .-zzz_victim
+
+	.section .eh_frame,"a",@progbits
+/* Hand-assembled so that no label-difference expressions are used.  MicroBlaze
+   GAS emits an R_MICROBLAZE_NONE marker for every resolved label difference,
+   which lands in .rela.eh_frame and trips the
+   BFD_ASSERT (cookie->rel->r_offset == ent->offset + 8) in
+   _bfd_elf_discard_section_eh_frame.  Literal lengths and CIE pointers keep
+   .rela.eh_frame to just the two FDE initial-location relocations. */
+
+	/* CIE at 0x00, total 20 bytes */
+	.4byte	16			/* length */
+	.4byte	0			/* CIE id */
+	.byte	1			/* version */
+	.asciz	"zR"			/* augmentation */
+	.uleb128 1			/* code alignment factor */
+	.sleb128 -4			/* data alignment factor */
+	.byte	15			/* return address register */
+	.uleb128 1			/* augmentation data length */
+	.byte	0x00			/* FDE encoding: DW_EH_PE_absptr */
+	.byte	0x0c, 0x01, 0x00	/* DW_CFA_def_cfa r1, 0 */
+
+	/* FDE for dead_fn at 0x14, total 20 bytes.  dead_fn is dropped by
+	   --gc-sections, so this FDE is removed and everything after it moves. */
+	.4byte	16			/* length */
+	.4byte	0x18			/* CIE pointer: this field's offset - 0 */
+	.4byte	dead_fn			/* initial location  <- the only reloc */
+	.4byte	8			/* address range */
+	.uleb128 0			/* augmentation data length */
+	.byte	0, 0, 0			/* padding to 20 bytes */
+
+ehlocal:				/* local symbol inside .eh_frame; it is
+					   this symbol moving that makes
+					   adjust_eh_frame_local_symbols() cache
+					   a locals-only symbol buffer */
+
+	/* FDE for aaa_relaxed at 0x28, total 20 bytes */
+	.4byte	16
+	.4byte	0x2c
+	.4byte	aaa_relaxed		/* <- the only other reloc */
+	.4byte	32
+	.uleb128 0
+	.byte	0, 0, 0
+
+	.4byte	0			/* terminator */
diff --git a/ld/testsuite/ld-microblaze/relax-addend-support.s b/ld/testsuite/ld-microblaze/relax-addend-support.s
new file mode 100644
index 00000000000..03d5eb0ffba
--- /dev/null
+++ b/ld/testsuite/ld-microblaze/relax-addend-support.s
@@ -0,0 +1,24 @@
+# Placed in .text.zz_support so that it is laid out after the sections of
+# relax-addend.s and the call from aaa_relaxed is a forward reference.  A
+# backward reference is not relaxed and the test would not exercise anything.
+
+	.section .text.zz_support,"ax",@progbits
+	.globl	near_callee
+	.type	near_callee,@function
+near_callee:
+	rtsd	r15, 8
+	nop
+	.size	near_callee, .-near_callee
+
+	.globl	_start
+_start:
+	brlid	r15, aaa_relaxed
+	nop
+	brlid	r15, zzz_victim
+	nop
+	bri	0
+
+	.data
+	.globl	gvar
+	.align	2
+gvar:	.space	64
diff --git a/ld/testsuite/ld-microblaze/relax-addend.d b/ld/testsuite/ld-microblaze/relax-addend.d
new file mode 100644
index 00000000000..951c8737696
--- /dev/null
+++ b/ld/testsuite/ld-microblaze/relax-addend.d
@@ -0,0 +1,26 @@
+#source: relax-addend.s
+#source: relax-addend-support.s
+#as: -EL
+#ld: -EL -relax --gc-sections -T $srcdir/$subdir/relax-addend.ld
+#objdump: -d
+#name: MicroBlaze relaxation preserves R_MICROBLAZE_64 addends
+
+# .text.aaa_relaxed contains an IMM that relaxation deletes.  .text.zzz_victim,
+# a sibling section of the same object, refers to gvar + 0x18.  The linker must
+# not let the deletion disturb that addend.
+#
+# The linker script pins .data, so gvar is at 0x90001000 and the reference must
+# resolve to 0x90001018, encoded as IMM 0x9000 followed by LWI with 0x1018.
+# A linker which corrupts the addend emits e8601014 instead.
+
+.*: +file format .*
+#...
+90000000 <aaa_relaxed>:
+[ 	]*90000000:[ 	]+3021ffe4[ 	]+addik[ 	]+r1, r1, -28
+[ 	]*90000004:[ 	]+f9e10000[ 	]+swi[ 	]+r15, r1, 0
+[ 	]*90000008:[ 	]+b9f40024[ 	]+brlid[ 	]+r15, 36
+#...
+9000001c <zzz_victim>:
+[ 	]*9000001c:[ 	]+b0009000[ 	]+imm[ 	]+-28672
+[ 	]*90000020:[ 	]+e8601018[ 	]+lwi[ 	]+r3, r0, 4120
+#pass
diff --git a/ld/testsuite/ld-microblaze/relax-addend.ld b/ld/testsuite/ld-microblaze/relax-addend.ld
new file mode 100644
index 00000000000..ca4d3603989
--- /dev/null
+++ b/ld/testsuite/ld-microblaze/relax-addend.ld
@@ -0,0 +1,23 @@
+/* Fixed layout so that the expected dump is deterministic.  gvar is the first
+   thing in .data, which is pinned, so the reference to gvar + 0x18 has a known
+   value regardless of how the sections happen to be ordered.  */
+ENTRY(_start)
+SECTIONS
+{
+  . = 0x90000000;
+  .text : {
+    *(.text.aaa_relaxed)
+    *(.text.zzz_victim)
+    *(.text.zz_support)
+    *(.text)
+    *(.text.*)
+  }
+  . = 0x90001000;
+  .data : {
+    *(.data)
+    *(.data.*)
+  }
+  . = 0x90001100;
+  .checkdata : { KEEP (*(.checkdata)) }
+  /DISCARD/ : { *(.comment) *(.note*) }
+}
diff --git a/ld/testsuite/ld-microblaze/relax-addend.s b/ld/testsuite/ld-microblaze/relax-addend.s
new file mode 100644
index 00000000000..16e500170fb
--- /dev/null
+++ b/ld/testsuite/ld-microblaze/relax-addend.s
@@ -0,0 +1,55 @@
+# Linker relaxation must not disturb the addend of an R_MICROBLAZE_64
+# relocation that refers to a symbol outside the section being relaxed.
+#
+# .text.aaa_relaxed contains an IMM that relaxation deletes.  .text.zzz_victim,
+# a sibling section in the same object file, contains
+#
+#	R_MICROBLAZE_64  gvar + 0x18
+#
+# While relaxing .text.aaa_relaxed, microblaze_elf_relax_section() walks the
+# relocations of every other section of the same BFD and, for R_MICROBLAZE_64,
+# indexes isymbuf with ELF32_R_SYM (irelscan->r_info) without checking it
+# against symtab_hdr->sh_info.  gvar is global, so its symbol index is >=
+# sh_info and the read is out of bounds -- isymbuf holds only sh_info entries
+# once --gc-sections has installed the locals-only cache.  If the bytes read
+# happen to satisfy
+#
+#	isym->st_shndx == shndx && ELF32_ST_TYPE (isym->st_info) == STT_SECTION
+#
+# the addend is decremented by calc_fixup(), and gvar + 0x18 links as
+# gvar + 0x14.
+#
+# The out-of-bounds read itself is unconditional; run ld under ASan or
+# valgrind to observe it.  Whether it corrupts the addend depends on what is
+# in the adjacent heap, so the check below is a correctness assertion rather
+# than a reliable trigger.
+
+	.section .text.aaa_relaxed,"ax",@progbits
+	.globl	aaa_relaxed
+	.type	aaa_relaxed,@function
+aaa_relaxed:
+	addik	r1, r1, -28
+	swi	r15, r1, 0
+	brlid	r15, near_callee	# IMM + BRLID; the IMM is deleted
+	nop
+	lwi	r15, r1, 0
+	rtsd	r15, 8
+	addik	r1, r1, 28
+	.size	aaa_relaxed, .-aaa_relaxed
+
+	.section .text.zzz_victim,"ax",@progbits
+	.globl	zzz_victim
+	.type	zzz_victim,@function
+zzz_victim:
+	lwi	r3, r0, gvar+24		# IMM + LWI; R_MICROBLAZE_64 gvar+0x18
+	rtsd	r15, 8
+	nop
+	.size	zzz_victim, .-zzz_victim
+
+/* A data reference to the same symbol with the same non-zero addend.  This
+   goes through the R_MICROBLAZE_32 arm of the same loop, and unlike the
+   instruction above it can be checked with readelf alone.  */
+	.section .checkdata,"aw",@progbits
+	.globl	check_word
+check_word:
+	.4byte	gvar + 0x18
-- 
2.25.1