[PATCH v2] ld: fix alignment issue for ARM thumb long branch stub using PureCode section

[Torbjörn SVENSSON]

Changes since v1:

- Simplified new test case to fix issue reported by Linaro CI.

Ok for trunk?

--

When pure-code option is activated. The linker creates for M-profile architecures
a 2-bytes branch instruction. This causes the section alignment to be set to 2-byte
alignment instead of 4-byte alignment. This is a problem for long branch stub
without pure-code section as it contains a 32-bit address as data, which is expected
to be 4-byte aligned. Hence creating a long branch stub for PureCode section followed
by a long branch stub will result in a misalignment for the 32-bit address.

An easy fix is to add a nop instruction after the branch to keep the section alignment
to 4 bytes.

Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>
Co-authored-by: Guillaume VACHERIAS <guillaume.vacherias@st.com>
---
 bfd/elf32-arm.c                               |  1 +
 ld/testsuite/ld-arm/arm-elf.exp               |  3 ++
 ...rcall-thumb2-purecode-consecutive-veneer.d | 28 +++++++++++++++++++
 ...rcall-thumb2-purecode-consecutive-veneer.s | 25 +++++++++++++++++
 ld/testsuite/ld-arm/farcall-thumb2-purecode.d |  2 +-
 5 files changed, 58 insertions(+), 1 deletion(-)
 create mode 100644 ld/testsuite/ld-arm/farcall-thumb2-purecode-consecutive-veneer.d
 create mode 100644 ld/testsuite/ld-arm/farcall-thumb2-purecode-consecutive-veneer.s

diff --git a/bfd/elf32-arm.c b/bfd/elf32-arm.c
index a4c23216c68..b22ca579493 100644
--- a/bfd/elf32-arm.c
+++ b/bfd/elf32-arm.c
@@ -2630,6 +2630,7 @@ static const insn_sequence elf32_arm_stub_long_branch_thumb2_only_pure[] =
   THUMB32_MOVW (0xf2400c00),	     /* mov.w ip, R_ARM_MOVW_ABS_NC */
   THUMB32_MOVT (0xf2c00c00),	     /* movt  ip, R_ARM_MOVT_ABS << 16 */
   THUMB16_INSN (0x4760),	     /* bx   ip */
+  THUMB16_INSN (0xbf00),	     /* nop */
 };
 
 /* V4T Thumb -> Thumb long branch stub. Using the stack is not
diff --git a/ld/testsuite/ld-arm/arm-elf.exp b/ld/testsuite/ld-arm/arm-elf.exp
index 7fa4520fb15..0f8beb3236c 100644
--- a/ld/testsuite/ld-arm/arm-elf.exp
+++ b/ld/testsuite/ld-arm/arm-elf.exp
@@ -604,6 +604,9 @@ set armeabitests_nonacl {
     {"Thumb2 purecode farcall" "-Ttext 0x1000 --section-start .foo=0x2001020" "" "" {farcall-thumb2-purecode.s}
      {{objdump -d farcall-thumb2-purecode.d}}
      "farcall-thumb2-purecode"}
+     {"Thumb2 purecode farcall consecutive veneer" "-Ttext 0x1000 --section-start .foo=0x2001020" "" "" {farcall-thumb2-purecode-consecutive-veneer.s}
+     {{objdump -d farcall-thumb2-purecode-consecutive-veneer.d}}
+     "farcall-thumb2-purecode-consecutive-veneer"}
 
     {"Thumb-ARM farcall" "-Ttext 0x1c01010 --section-start .foo=0x2001014" "" "-W" {farcall-thumb-arm.s}
      {{objdump -d farcall-thumb-arm.d}}
diff --git a/ld/testsuite/ld-arm/farcall-thumb2-purecode-consecutive-veneer.d b/ld/testsuite/ld-arm/farcall-thumb2-purecode-consecutive-veneer.d
new file mode 100644
index 00000000000..b89da03eec0
--- /dev/null
+++ b/ld/testsuite/ld-arm/farcall-thumb2-purecode-consecutive-veneer.d
@@ -0,0 +1,28 @@
+.*:     file format .*
+
+Disassembly of section .text:
+
+00001000 <bar>:
+    1000:	4770      	bx	lr
+
+00001002 <baz>:
+    1002:	4770      	bx	lr
+
+Disassembly of section .foo:
+
+02001020 <_start>:
+ 2001020:	f000 f802 	bl	2001028 <__bar_veneer>
+ 2001024:	f000 f806 	bl	2001034 <__baz_veneer>
+
+02001028 <__bar_veneer>:
+ 2001028:	f241 0c01 	movw	ip, #4097	@ 0x1001
+ 200102c:	f2c0 0c00 	movt	ip, #0
+ 2001030:	4760      	bx	ip
+ 2001032:	bf00      	nop
+
+02001034 <__baz_veneer>:
+ 2001034:	f241 0c03 	movw	ip, #4099	@ 0x1003
+ 2001038:	f2c0 0c00 	movt	ip, #0
+ 200103c:	4760      	bx	ip
+ 200103e:	bf00      	nop
+	\.\.\.
diff --git a/ld/testsuite/ld-arm/farcall-thumb2-purecode-consecutive-veneer.s b/ld/testsuite/ld-arm/farcall-thumb2-purecode-consecutive-veneer.s
new file mode 100644
index 00000000000..ee3d6c10b7b
--- /dev/null
+++ b/ld/testsuite/ld-arm/farcall-thumb2-purecode-consecutive-veneer.s
@@ -0,0 +1,25 @@
+@ Test to ensure that a purecode Thumb2 call exceeding 4Mb generates a stub.
+
+	.global _start
+	.syntax unified
+	.arch armv7-m
+	.thumb
+	.thumb_func
+
+@ We will place the section .text at 0x1000.
+
+	.section .text, "0x20000006"
+	.type bar, %function
+	.type baz, %function
+bar:
+	bx lr
+
+baz:
+	bx lr
+
+@ We will place the section .foo at 0x02001014.
+
+	.section .foo, "0x20000006"
+_start:
+	bl bar
+	bl baz
diff --git a/ld/testsuite/ld-arm/farcall-thumb2-purecode.d b/ld/testsuite/ld-arm/farcall-thumb2-purecode.d
index 451832678e9..00a070eed5b 100644
--- a/ld/testsuite/ld-arm/farcall-thumb2-purecode.d
+++ b/ld/testsuite/ld-arm/farcall-thumb2-purecode.d
@@ -16,7 +16,7 @@ Disassembly of section .foo:
  2001028:	f241 0c01 	movw	ip, #4097	@ 0x1001
  200102c:	f2c0 0c00 	movt	ip, #0
  2001030:	4760      	bx	ip
- 2001032:	0000      	movs	r0, r0
+ 2001032:	bf00      	nop
  2001034:	0000      	movs	r0, r0
 	\.\.\.
 
-- 
2.25.1