[lld] [lld][ARM] Don't emit veneers for wraparound branches. (PR #165263)

[Peter Smith via llvm-commits]

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@@ -0,0 +1,118 @@
+// REQUIRES: arm
+// RUN: rm -rf %t && split-file %s %t && cd %t
+// RUN: llvm-mc -filetype=obj -triple=armv7-none-eabi code.s -o code.o
+// RUN: ld.lld -T unsigned1.ld code.o -o unsigned1.elf
+// RUN: llvm-objdump --triple=armv7 -d unsigned1.elf | FileCheck %s --check-prefix=UNSIGNED1
+// RUN: ld.lld -T unsigned2.ld code.o -o unsigned2.elf
+// RUN: llvm-objdump --triple=armv7 -d unsigned2.elf | FileCheck %s --check-prefix=UNSIGNED2
+// RUN: ld.lld -T signed1.ld code.o -o signed1.elf
+// RUN: llvm-objdump --triple=armv7 -d signed1.elf | FileCheck %s --check-prefix=SIGNED1
+// RUN: ld.lld -T signed2.ld code.o -o signed2.elf
+// RUN: llvm-objdump --triple=armv7 -d signed2.elf | FileCheck %s --check-prefix=SIGNED2
+
+// The aim of this test is to ensure that a BL instruction near one end of the
+// address space can reach a function at the extreme other end, directly, using
+// a branch offset that makes the address wrap round. We check this at both the
+// unsigned wraparound point (one address near 0 and the other near 0xFFFFFFFF)
+// and the signed wraparound point (addresses either side of 0x80000000),
+// crossing the boundary in both directions. In all four cases we expect a
+// direct branch with no veneer.
+
+// UNSIGNED1: Disassembly of section .text.lowaddr:
+// UNSIGNED1: 00010000 <func>:
+// UNSIGNED1:    10000: e12fff1e      bx      lr
+//
+// UNSIGNED1: Disassembly of section .text.highaddr:
+// UNSIGNED1: ffff0000 <_start>:
+// UNSIGNED1: ffff0000: eb007ffe      bl      0x10000
+// UNSIGNED1: ffff0004: e12fff1e      bx      lr
+
+// UNSIGNED2: Disassembly of section .text.lowaddr:
+// UNSIGNED2: 00010000 <_start>:
+// UNSIGNED2:    10000: ebff7ffe      bl      0xffff0000
+// UNSIGNED2:    10004: e12fff1e      bx      lr
+//
+// UNSIGNED2: Disassembly of section .text.highaddr:
+// UNSIGNED2: ffff0000 <func>:
+// UNSIGNED2: ffff0000: e12fff1e      bx      lr
+
+// SIGNED1:   Disassembly of section .text.posaddr:
+// SIGNED1:   7fff0000 <_start>:
+// SIGNED1:   7fff0000: eb007ffe      bl      0x80010000
+// SIGNED1:   7fff0004: e12fff1e      bx      lr
+//
+// SIGNED1:   Disassembly of section .text.negaddr:
+// SIGNED1:   80010000 <func>:
+// SIGNED1:   80010000: e12fff1e      bx      lr
+
+// SIGNED2:   Disassembly of section .text.posaddr:
+// SIGNED2:   7fff0000 <func>:
+// SIGNED2:   7fff0000: e12fff1e      bx      lr
+//
+// SIGNED2:   Disassembly of section .text.negaddr:
+// SIGNED2:   80010000 <_start>:
+// SIGNED2:   80010000: ebff7ffe      bl      0x7fff0000
+// SIGNED2:   80010004: e12fff1e      bx      lr
+
+//--- code.s
+
+  .section .text.callee, "ax", %progbits
+  .global func
+  .type func, %function
+func:
+  bx lr
+
+  .section .text.caller, "ax", %progbits
+  .global _start
+  .type _start, %function
+_start:
+  bl func
+  bx lr
+
+//--- unsigned1.ld
+
+ENTRY(_start)
+PHDRS {
----------------
smithp35 wrote:

I don't think you need the PHDRS here. To get LLD to create a separate program header for each output section you can use AT.

`.text.lowaddr 0x00010000 : AT(0x00010000)  { *(.text.callee) }`

https://github.com/llvm/llvm-project/pull/165263