[MC][ELF][ARM] Add relocations for some pc-relative fixups

Add ELF relocations for the following fixups:
fixup_thumb_adr_pcrel_10 -> R_ARM_THM_PC8
fixup_thumb_cp -> R_ARM_THM_PC8
fixup_t2_adr_pcrel_12 -> R_ARM_THM_PREL_11_0
fixup_t2_ldst_pcrel_12 -> R_ARM_THM_PC12

While these relocations are short-ranged there is support in the open
source ELF linker's in binutils and soon to be in LLD. MC will no longer
resolve pc-relative fixups to global symbols due to interpositioning
concerns. We can handle these at link time by implementing the relocations.

The R_ARM_THM_PC8 has some extra encoding rules for addends that llvm-mc
sidesteps by not supporting addends for these instructions, using the wide
Thumb 2 instruction if it is available. I think that this is a reasonable
compromise given that these are rare.

This partiall reverts D72892, the Thumb fixups no longer need to be
evaluated at assembly time.

Differential Revision: https://reviews.llvm.org/D75039

diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
index 66ac276..d118b4f 100644 (file)
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
@@ -64,7 +64,8 @@ const MCFixupKindInfo &ARMAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
       // Name                      Offset (bits) Size (bits)     Flags
       {"fixup_arm_ldst_pcrel_12", 0, 32, IsPCRelConstant},
       {"fixup_t2_ldst_pcrel_12", 0, 32,
-       IsPCRelConstant | MCFixupKindInfo::FKF_IsAlignedDownTo32Bits},
+       MCFixupKindInfo::FKF_IsPCRel |
+           MCFixupKindInfo::FKF_IsAlignedDownTo32Bits},
       {"fixup_arm_pcrel_10_unscaled", 0, 32, IsPCRelConstant},
       {"fixup_arm_pcrel_10", 0, 32, IsPCRelConstant},
       {"fixup_t2_pcrel_10", 0, 32,
@@ -74,10 +75,12 @@ const MCFixupKindInfo &ARMAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
       {"fixup_t2_pcrel_9", 0, 32,
        IsPCRelConstant | MCFixupKindInfo::FKF_IsAlignedDownTo32Bits},
       {"fixup_thumb_adr_pcrel_10", 0, 8,
-       IsPCRelConstant | MCFixupKindInfo::FKF_IsAlignedDownTo32Bits},
+       MCFixupKindInfo::FKF_IsPCRel |
+           MCFixupKindInfo::FKF_IsAlignedDownTo32Bits},
       {"fixup_arm_adr_pcrel_12", 0, 32, IsPCRelConstant},
       {"fixup_t2_adr_pcrel_12", 0, 32,
-       IsPCRelConstant | MCFixupKindInfo::FKF_IsAlignedDownTo32Bits},
+       MCFixupKindInfo::FKF_IsPCRel |
+           MCFixupKindInfo::FKF_IsAlignedDownTo32Bits},
       {"fixup_arm_condbranch", 0, 24, MCFixupKindInfo::FKF_IsPCRel},
       {"fixup_arm_uncondbranch", 0, 24, MCFixupKindInfo::FKF_IsPCRel},
       {"fixup_t2_condbranch", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
@@ -109,8 +112,7 @@ const MCFixupKindInfo &ARMAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
       {"fixup_bfc_target", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
       {"fixup_bfcsel_else_target", 0, 32, 0},
       {"fixup_wls", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
-      {"fixup_le", 0, 32, MCFixupKindInfo::FKF_IsPCRel}
-  };
+      {"fixup_le", 0, 32, MCFixupKindInfo::FKF_IsPCRel}};
   const static MCFixupKindInfo InfosBE[ARM::NumTargetFixupKinds] = {
       // This table *must* be in the order that the fixup_* kinds are defined in
       // ARMFixupKinds.h.

diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
index 2c26dd3..1e2399c 100644 (file)
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
@@ -137,6 +137,13 @@ unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
       default:
         return ELF::R_ARM_THM_CALL;
       }
+    case ARM::fixup_thumb_adr_pcrel_10:
+    case ARM::fixup_arm_thumb_cp:
+      return ELF::R_ARM_THM_PC8;
+    case ARM::fixup_t2_adr_pcrel_12:
+      return ELF::R_ARM_THM_ALU_PREL_11_0;
+    case ARM::fixup_t2_ldst_pcrel_12:
+      return ELF::R_ARM_THM_PC12;
     case ARM::fixup_bf_target:
       return ELF::R_ARM_THM_BF16;
     case ARM::fixup_bfc_target:

diff --git a/llvm/test/MC/ARM/pcrel-global-rel.s b/llvm/test/MC/ARM/pcrel-global-rel.s
new file mode 100644 (file)
index 0000000..f1a71e6
--- /dev/null
+++ b/llvm/test/MC/ARM/pcrel-global-rel.s
@@ -0,0 +1,18 @@
+@ RUN: llvm-mc -filetype=obj -triple=armv7 %s -o %t
+@ RUN: llvm-readobj -r %t
+
+@ Check that for ELF targets we generate a relocation for a within section
+@ pc-relative reference to a global symbol as it may be interposed and we won't
+@ know till link time whether this is possible.
+.thumb
+.thumb_func
+
+.globl bar
+bar:
+adr r0, bar      @ thumb_adr_pcrel_10
+adr.w r0, bar    @ t2_adr_pcrel_12
+ldr.w pc, bar    @ t2_ldst_pcrel_12
+
+@ CHECK:      0x0 R_ARM_THM_ALU_PREL_11_0 bar 0x0
+@ CHECK-NEXT: 0x4 R_ARM_THM_ALU_PREL_11_0 bar 0x0
+@ CHECK-NEXT: 0x8 R_ARM_THM_PC12 bar 0x0

diff --git a/llvm/test/MC/ARM/pcrel-global.s b/llvm/test/MC/ARM/pcrel-global.s
index cec6c1c..c1ab435 100644 (file)
--- a/llvm/test/MC/ARM/pcrel-global.s
+++ b/llvm/test/MC/ARM/pcrel-global.s
@@ -11,11 +11,3 @@ vldr d0, foo     @ arm_pcrel_10
 adr r2, foo      @ arm_adr_pcrel_12
 ldr r0, foo      @ arm_ldst_pcrel_12
 
-.thumb
-.thumb_func
-
-.globl bar
-bar:
-adr r0, bar      @ thumb_adr_pcrel_10
-adr.w r0, bar    @ t2_adr_pcrel_12
-ldr.w pc, bar    @ t2_ldst_pcrel_12

diff --git a/llvm/test/MC/ARM/thumb1-relax-adr.s b/llvm/test/MC/ARM/thumb1-relax-adr.s
index 80b93ec..213c968 100644 (file)
--- a/llvm/test/MC/ARM/thumb1-relax-adr.s
+++ b/llvm/test/MC/ARM/thumb1-relax-adr.s
@@ -1,9 +1,11 @@
 @ RUN: not llvm-mc -triple thumbv6m-none-macho -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
 @ RUN: not llvm-mc -triple thumbv7m-none-macho -filetype=obj -o /dev/null %s 2>&1  | FileCheck --check-prefix=CHECK-ERROR %s
-@ RUN: not llvm-mc -triple thumbv7m-none-eabi -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
+@ RUN: llvm-mc -triple thumbv6m-none-eabi -filetype=obj %s -o - | llvm-readobj --relocs | FileCheck --check-prefix=CHECK-ELF-T1 %s
+@ RUN: llvm-mc -triple thumbv7m-none-eabi -filetype=obj %s -o - | llvm-readobj --relocs | FileCheck --check-prefix=CHECK-ELF-T2 %s
 
         .global func1
 _func1:
         adr r0, _func2
 @ CHECK-ERROR: unsupported relocation on symbol
-
+@ CHECK-ELF-T1: 0x0 R_ARM_THM_PC8 _func2 0x0
+@ CHECK-ELF-T2: 0x0 R_ARM_THM_ALU_PREL_11_0 _func2 0x0

diff --git a/llvm/test/MC/ARM/thumb1-relax-ldrlit.s b/llvm/test/MC/ARM/thumb1-relax-ldrlit.s
index 96c5aa0..e65ee52 100644 (file)
--- a/llvm/test/MC/ARM/thumb1-relax-ldrlit.s
+++ b/llvm/test/MC/ARM/thumb1-relax-ldrlit.s
@@ -1,9 +1,11 @@
 @ RUN: not llvm-mc -triple thumbv6m-none-macho -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
 @ RUN: not llvm-mc -triple thumbv7m-none-macho -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
-@ RUN: not llvm-mc -triple thumbv7m-none-eabi -filetype=obj -o /dev/null %s 2>&1 | FileCheck --check-prefix=CHECK-ERROR %s
+@ RUN: llvm-mc -triple thumbv6m-none-eabi -filetype=obj %s -o - | llvm-readobj --relocs | FileCheck --check-prefix=CHECK-ELF-T1 %s
+@ RUN: llvm-mc -triple thumbv7m-none-eabi -filetype=obj %s -o - | llvm-readobj --relocs | FileCheck --check-prefix=CHECK-ELF-T2 %s
 
         .global func1
 _func1:
         ldr r0, _func2
 @ CHECK-ERROR: unsupported relocation on symbol
-
+@ CHECK-ELF-T1: 0x0 R_ARM_THM_PC8 _func2 0x0
+@ CHECK-ELF-T2: 0x0 R_ARM_THM_PC12 _func2 0x0