Reapply "[lld] Support thumb PLTs" (#93631) (#93644)

This reverts commit 7832769d329ead264aff238c06dce086b3a74922.

This was reverted prior due to a test failure on the windows builder. I
think this was because we didn't specify the triple and assumed windows.
The other tests use the full triple specifying linux, so we follow suite
here.

---

We are using PLTs for cortex-m33 which only supports thumb. More
specifically, this is for a very restricted use case. There's no MMU so
there's no sharing of virtual addresses between two processes, but this
is fine. The MCU is used for running [chre
nanoapps](https://android.googlesource.com/platform/system/chre/+/HEAD/doc/nanoapp_overview.md)
for android. Each nanoapp is a shared library (but effectively acts as
an executable containing a test suite) that is loaded and run on the MCU
one binary at a time and there's only one process running at a time, so
we ensure that the same text segment cannot be shared by two different
running executables. GNU LD supports thumb PLTs but we want to migrate
to a clang toolchain and use LLD, so thumb PLTs are needed.

1 files changed, 126 insertions, 0 deletions

diff --git a/lld/test/ELF/armv8-thumb-plt-reloc.s b/lld/test/ELF/armv8-thumb-plt-reloc.s
new file mode 100644
index 0000000..5b6e4b5
--- /dev/null
+++ b/lld/test/ELF/armv8-thumb-plt-reloc.s
@@ -0,0 +1,126 @@
+// REQUIRES: arm
+// RUN: llvm-mc -filetype=obj -arm-add-build-attributes -triple=thumbv8-none-linux-gnueabi --arch=thumb --mcpu=cortex-m33 %p/Inputs/arm-plt-reloc.s -o %t1.o
+// RUN: llvm-mc -filetype=obj -arm-add-build-attributes -triple=thumbv8-none-linux-gnueabi --arch=thumb --mcpu=cortex-m33 %s -o %t2.o
+// RUN: ld.lld %t1.o %t2.o -o %t
+// RUN: llvm-objdump --no-print-imm-hex -d %t | FileCheck %s
+// RUN: ld.lld -shared %t1.o %t2.o -o %t.so
+// RUN: llvm-objdump --no-print-imm-hex -d %t.so | FileCheck --check-prefix=DSO %s
+// RUN: llvm-readelf -S -r %t.so | FileCheck -check-prefix=DSOREL %s
+
+// RUN: llvm-mc -filetype=obj -arm-add-build-attributes -triple=thumbv8-none-linux-gnueabi --arch=thumbeb --mcpu=cortex-m33 %p/Inputs/arm-plt-reloc.s -o %t1.be.o
+// RUN: llvm-mc -filetype=obj -arm-add-build-attributes -triple=thumbv8-none-linux-gnueabi --arch=thumbeb --mcpu=cortex-m33 %s -o %t2.be.o
+// RUN: ld.lld %t1.be.o %t2.be.o -o %t.be
+// RUN: llvm-objdump --no-print-imm-hex -d %t.be | FileCheck %s
+// RUN: ld.lld -shared %t1.be.o %t2.be.o -o %t.so.be
+// RUN: llvm-objdump --no-print-imm-hex -d %t.so.be | FileCheck --check-prefix=DSO %s
+// RUN: llvm-readelf -S -r %t.so.be | FileCheck -check-prefix=DSOREL %s
+
+// RUN: ld.lld --be8 %t1.be.o %t2.be.o -o %t.be
+// RUN: llvm-objdump --no-print-imm-hex -d %t.be | FileCheck %s
+// RUN: ld.lld --be8 -shared %t1.be.o %t2.be.o -o %t.so.be
+// RUN: llvm-objdump --no-print-imm-hex -d %t.so.be | FileCheck --check-prefix=DSO %s
+// RUN: llvm-readelf -S -r %t.so.be | FileCheck -check-prefix=DSOREL %s
+
+/// Test PLT entry generation
+ .text
+ .align 2
+ .globl _start
+ .type  _start,%function
+_start:
+ bl func1
+ bl func2
+ bl func3
+ b.w func1
+ b.w func2
+ b.w func3
+ beq.w func1
+ beq.w func2
+ beq.w func3
+
+/// Executable, expect no PLT
+// CHECK: Disassembly of section .text:
+// CHECK-EMPTY:
+// CHECK-NEXT: <func1>:
+// CHECK-NEXT:   bx      lr
+// CHECK: <func2>:
+// CHECK-NEXT:   bx      lr
+// CHECK: <func3>:
+// CHECK-NEXT:   bx      lr
+// CHECK-NEXT:   d4d4 
+// CHECK: <_start>:
+// CHECK-NEXT:   bl      {{.*}} <func1>
+// CHECK-NEXT:   bl      {{.*}} <func2>
+// CHECK-NEXT:   bl      {{.*}} <func3>
+// CHECK-NEXT:   b.w     {{.*}} <func1>
+// CHECK-NEXT:   b.w     {{.*}} <func2>
+// CHECK-NEXT:   b.w     {{.*}} <func3>
+// CHECK-NEXT:   beq.w	 {{.*}} <func1>
+// CHECK-NEXT:   beq.w	 {{.*}} <func2>
+// CHECK-NEXT:   beq.w	 {{.*}} <func3>
+
+// DSO: Disassembly of section .text:
+// DSO-EMPTY:
+// DSO-NEXT: <func1>:
+// DSO-NEXT:     bx      lr
+// DSO: <func2>:
+// DSO-NEXT:     bx      lr
+// DSO: <func3>:
+// DSO-NEXT:     bx      lr
+// DSO-NEXT:     d4d4 
+// DSO: <_start>:
+/// 0x10260 = PLT func1
+// DSO-NEXT:     bl     0x10260
+/// 0x10270 = PLT func2
+// DSO-NEXT:     bl     0x10270
+/// 0x10280 = PLT func3
+// DSO-NEXT:     bl     0x10280
+/// 0x10260 = PLT func1
+// DSO-NEXT:     b.w    0x10260
+/// 0x10270 = PLT func2
+// DSO-NEXT:     b.w    0x10270
+/// 0x10280 = PLT func3
+// DSO-NEXT:     b.w    0x10280
+/// 0x10260 = PLT func1
+// DSO-NEXT:     beq.w	 0x10260
+/// 0x10270 = PLT func2
+// DSO-NEXT:     beq.w	 0x10270
+/// 0x10280 = PLT func3
+// DSO-NEXT:     beq.w	 0x10280
+// DSO: Disassembly of section .plt:
+// DSO-EMPTY:
+// DSO-NEXT: 10240 <.plt>:
+// DSO-NEXT:     push    {lr}
+// DSO-NEXT:     ldr.w   lr, [pc, #8]
+// DSO-NEXT:     add     lr, pc
+// DSO-NEXT:     ldr     pc, [lr, #8]!
+/// 0x20098 = .got.plt (0x302D8) - pc (0x10238 = .plt + 8) - 8
+// DSO-NEXT:     .word   0x00020098
+// DSO-NEXT:     .word   0xd4d4d4d4
+// DSO-NEXT:     .word   0xd4d4d4d4
+// DSO-NEXT:     .word   0xd4d4d4d4
+// DSO-NEXT:     .word   0xd4d4d4d4
+
+/// 136 + 2 << 16 + 0x1026c = 0x302f4 = got entry 1
+// DSO-NEXT:     10260:       f240 0c88     movw    r12, #136
+// DSO-NEXT:                  f2c0 0c02     movt    r12, #2
+// DSO-NEXT:                  44fc          add     r12, pc
+// DSO-NEXT:                  f8dc f000     ldr.w   pc, [r12]
+// DSO-NEXT:                  e7fc          b       0x1026a
+/// 124 + 2 << 16 + 0x1027c = 0x302f8 = got entry 2
+// DSO-NEXT:     10270:       f240 0c7c     movw    r12, #124
+// DSO-NEXT:                  f2c0 0c02     movt    r12, #2
+// DSO-NEXT:                  44fc          add     r12, pc
+// DSO-NEXT:                  f8dc f000     ldr.w   pc, [r12]
+// DSO-NEXT:                  e7fc          b       0x1027a
+/// 112 + 2 << 16 + 0x1028c = 0x302fc = got entry 3
+// DSO-NEXT:     10280:       f240 0c70     movw    r12, #112
+// DSO-NEXT:                  f2c0 0c02     movt    r12, #2
+// DSO-NEXT:                  44fc          add     r12, pc
+// DSO-NEXT:                  f8dc f000     ldr.w   pc, [r12]
+// DSO-NEXT:                  e7fc          b       0x1028a
+
+// DSOREL: .got.plt PROGBITS 000302e8 {{.*}} 000018 00  WA  0   0  4
+// DSOREL: Relocation section '.rel.plt'
+// DSOREL: 000302f4 {{.*}} R_ARM_JUMP_SLOT {{.*}} func1
+// DSOREL: 000302f8 {{.*}} R_ARM_JUMP_SLOT {{.*}} func2
+// DSOREL: 000302fc {{.*}} R_ARM_JUMP_SLOT {{.*}} func3