[ELF][ARM] Add test case that will fail if toPlt() is removed [NFC]

When a thunk is created to a PLT entry, the call to the thunk is converted
to a non-plt expression with fromPlt(). If the thunk becomes unusable we
retarget the relocation back to its original target and try again. When we
do this we need to make sure that we restore the PLT form of the expression
with toPlt().

This change adds a test case that will fail if toPlt() is removed. We need
to have a call to a preemptible symbol defined within the link unit. If
toPlt() is removed then the relocation to the thunk to the PLT entry for the
preemptible symbol will be retargeted to the preemptible symbol itself
instead of its PLT entry.

Differential Revision: https://reviews.llvm.org/D57743

llvm-svn: 353285

lld/test/ELF/arm-thunk-multipass-plt.s

@@ -0,0 +1,94 @@
+// REQUIRES: arm
+// RUN: llvm-mc -arm-add-build-attributes -filetype=obj -triple=armv5-none-linux-gnueabi %s -o %t
+// RUN: ld.lld %t -o %t2 --shared 2>&1
+// RUN: llvm-objdump --start-address=7340044 --stop-address=7340048 --triple=armv5-none-linux-gnueabi -d %t2 | FileCheck %s
+// RUN: llvm-objdump --start-address=8388620 --stop-address=8388624 --triple=thumbv5-none-linux-gnueabi -d %t2 | FileCheck %s -check-prefix=CHECK-CALL
+// RUN: llvm-objdump --start-address=13631520 --stop-address=13631584 --triple=armv5-none-linux-gnueabi -d %t2 | FileCheck %s -check-prefix=CHECK-PLT
+// When we create a thunk to a PLT entry the relocation is redirected to the
+// Thunk, changing its expression to a non-PLT equivalent. If the thunk
+// becomes unusable we need to restore the relocation expression to the PLT
+// form so that when we create a new thunk it targets the PLT.
+
+// Test case that checks the case:
+// - Thunk is created on pass 1 to a PLT entry for preemptible
+// - Some other Thunk added in the same pass moves the thunk to
+// preemptible out of range of its caller.
+// - New Thunk is created on pass 2 to PLT entry for preemptible
+
+        .globl preemptible
+        .globl preemptible2
+.section .text.01, "ax", %progbits
+.balign 0x100000
+        .thumb
+        .globl needsplt
+        .type needsplt, %function
+needsplt:
+        bl preemptible
+        .section .text.02, "ax", %progbits
+        .space (1024 * 1024)
+
+        .section .text.03, "ax", %progbits
+        .space (1024 * 1024)
+
+        .section .text.04, "ax", %progbits
+        .space (1024 * 1024)
+
+        .section .text.05, "ax", %progbits
+        .space (1024 * 1024)
+
+        .section .text.06, "ax", %progbits
+        .space (1024 * 1024)
+
+        .section .text.07, "ax", %progbits
+        .space (1024 * 1024)
+// 0x70000c + 8 + 0x60002c = 0xd00040 = preemptible@plt
+// CHECK: 000000000070000c __ARMV5PILongThunk_preemptible:
+// CHECK-NEXT:   70000c:        0b 00 18 ea     b       #6291500
+
+        .section .text.08, "ax", %progbits
+        .space (1024 * 1024) - 4
+
+        .section .text.10, "ax", %progbits
+        .balign 2
+        bl preemptible
+        bl preemptible2
+// 0x80000c + 4 - 100004 = 0x70000c = __ARMv5PILongThunk_preemptible
+// CHECK-CALL: 80000c:   ff f6 fe ef     blx     #-1048580
+        .balign 2
+        .globl preemptible
+        .type preemptible, %function
+preemptible:
+        bx lr
+        .globl preemptible2
+        .type preemptible2, %function
+preemptible2:
+        bx lr
+
+
+        .section .text.11, "ax", %progbits
+        .space (5 * 1024 * 1024)
+
+
+// CHECK-PLT: Disassembly of section .plt:
+// CHECK-PLT-NEXT: 0000000000d00020 $a:
+// CHECK-PLT-NEXT:   d00020:    04 e0 2d e5     str     lr, [sp, #-4]!
+// CHECK-PLT-NEXT:   d00024:    00 e6 8f e2     add     lr, pc, #0, #12
+// CHECK-PLT-NEXT:   d00028:    00 ea 8e e2     add     lr, lr, #0, #20
+// CHECK-PLT-NEXT:   d0002c:    dc ff be e5     ldr     pc, [lr, #4060]!
+// CHECK-PLT: 0000000000d00030 $d:
+// CHECK-PLT-NEXT:   d00030:    d4 d4 d4 d4     .word   0xd4d4d4d4
+// CHECK-PLT-NEXT:   d00034:    d4 d4 d4 d4     .word   0xd4d4d4d4
+// CHECK-PLT-NEXT:   d00038:    d4 d4 d4 d4     .word   0xd4d4d4d4
+// CHECK-PLT-NEXT:   d0003c:    d4 d4 d4 d4     .word   0xd4d4d4d4
+// CHECK-PLT: 0000000000d00040 $a:
+// CHECK-PLT-NEXT:   d00040:    00 c6 8f e2     add     r12, pc, #0, #12
+// CHECK-PLT-NEXT:   d00044:    00 ca 8c e2     add     r12, r12, #0, #20
+// CHECK-PLT-NEXT:   d00048:    c4 ff bc e5     ldr     pc, [r12, #4036]!
+// CHECK-PLT: 0000000000d0004c $d:
+// CHECK-PLT-NEXT:   d0004c:    d4 d4 d4 d4     .word   0xd4d4d4d4
+// CHECK-PLT: 0000000000d00050 $a:
+// CHECK-PLT-NEXT:   d00050:    00 c6 8f e2     add     r12, pc, #0, #12
+// CHECK-PLT-NEXT:   d00054:    00 ca 8c e2     add     r12, r12, #0, #20
+// CHECK-PLT-NEXT:   d00058:    b8 ff bc e5     ldr     pc, [r12, #4024]!
+// CHECK-PLT: 0000000000d0005c $d:
+// CHECK-PLT-NEXT:   d0005c:    d4 d4 d4 d4     .word   0xd4d4d4d4