llvm-project/lld/test/ELF/arm-undefined-weak.s

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// REQUIRES: arm
// RUN: llvm-mc -arm-add-build-attributes -filetype=obj -triple=armv7a-none-linux-gnueabi %s -o %t
// RUN: ld.lld --image-base=0x10000000 %t -o %t2
// RUN: llvm-objdump --triple=armv7a-none-linux-gnueabi --no-show-raw-insn -d %t2 | FileCheck %s
/// Check that the ARM ABI rules for undefined weak symbols are applied.
/// Branch instructions are resolved to the next instruction. Undefined
/// Symbols in relative are resolved to the place so S - P + A = A.
/// We place the image-base at 0x10000000 to test that a range extensions thunk
/// is not generated.
.syntax unified
.weak target
[LLD][ELF][ARM] Do not substitute BL/BLX for non STT_FUNC symbols. Recommit of 0b4a047bfbd11fe1f5abda8da0e2391c1918162a (reverted in c29003813ab9bd6ea7b6de40ea8f1fe21979f13f) to incorporate subsequent fix and add a warning when LLD's interworking behavior has changed. D73474 disabled the generation of interworking thunks for branch relocations to non STT_FUNC symbols. This patch handles the case of BL and BLX instructions to non STT_FUNC symbols. LLD would normally look at the state of the caller and the callee and write a BL if the states are the same and a BLX if the states are different. This patch disables BL/BLX substitution when the destination symbol does not have type STT_FUNC. This brings our behavior in line with GNU ld which may prevent difficult to diagnose runtime errors when switching to lld. This change does change how LLD handles interworking of symbols that do not have type STT_FUNC from previous versions including the 10.0 release. This brings LLD in line with ld.bfd but there may be programs that have not been linked with ld.bfd that depend on LLD's previous behavior. We emit a warning when the behavior changes. A summary of the difference between 10.0 and 11.0 is that for symbols that do not have a type of STT_FUNC LLD will not change a BL to a BLX or vice versa. The table below enumerates the changes | relocation | STT_FUNC | bit(0) | in | 10.0- out | 11.0+ out | | R_ARM_CALL | no | 1 | BL | BLX | BL | | R_ARM_CALL | no | 0 | BLX | BL | BLX | | R_ARM_THM_CALL | no | 1 | BLX | BL | BLX | | R_ARM_THM_CALL | no | 0 | BL | BLX | BL | Differential Revision: https://reviews.llvm.org/D73542
2020-02-13 16:42:17 +08:00
.type target, %function
.text
.global _start
_start:
/// R_ARM_JUMP24
b target
/// R_ARM_CALL
bl target
/// R_ARM_CALL with exchange
blx target
/// R_ARM_MOVT_PREL
movt r0, :upper16:target - .
/// R_ARM_MOVW_PREL_NC
movw r0, :lower16:target - .
/// R_ARM_REL32
.word target - .
// CHECK: Disassembly of section .text:
// CHECK-EMPTY:
// CHECK-NEXT: 100100b4 <_start>:
// CHECK-NEXT: 100100b4: b #-4
// CHECK-NEXT: 100100b8: bl #-4
// CHECK-NEXT: 100100bc: bl #-4
// CHECK-NEXT: 100100c0: movt r0, #0
// CHECK-NEXT: 100100c4: movw r0, #0
// CHECK: 100100c8: 00 00 00 00 .word 0x00000000