[llvm] bbc5d9f - [llvm][MC][ARM][Assembly] Emit relocations for LDRs (#72873)

via llvm-commits llvm-commits at lists.llvm.org
Sat Nov 25 04:36:06 PST 2023


Author: Eleanor Bonnici
Date: 2023-11-25T12:36:00Z
New Revision: bbc5d9fe427362f3fec8d147d5f7bc2d39b08e44

URL: https://github.com/llvm/llvm-project/commit/bbc5d9fe427362f3fec8d147d5f7bc2d39b08e44
DIFF: https://github.com/llvm/llvm-project/commit/bbc5d9fe427362f3fec8d147d5f7bc2d39b08e44.diff

LOG: [llvm][MC][ARM][Assembly] Emit relocations for LDRs (#72873)

It's possible (though inadvisable) to use LDR and refer to labels in
different
sections. In the Arm state, the assembler resolves the LDR instruction
without
emitting a relocation. That's incorrect because the assembler cannot
make any
assumptions about the relative position of the sections and the compiler
output
is therefore wrong.

This patch ensures relocations are generated for all `LDR <Rt...>,
label`
instructions in the Arm state (little endian). This is not necessary
when the
label is in the same section but the relocation is now generated
regardless.
Instructions that now generate relocations have been removed from the
pcrel-global.s test.

Fortunately, LLD already implements the generated relocations and can
fix LDR
instructions when the symbol is in a different section, or report an
error if
the offset is too large for the immediate field in the particular LDR's
encoding.

The patch to address this problem for big endian targets will follow, as
well
as a fix for ADR that exhibits a similar behavior.

Added: 
    llvm/test/MC/ARM/pcrel-arm-ldr-imm8-relocs.s
    llvm/test/MC/ARM/pcrel-ldr-relocs.s
    llvm/test/MC/ARM/pcrel-thumb-ldr2-relocs.s

Modified: 
    llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
    llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
    llvm/test/MC/ARM/pcrel-global.s
    llvm/test/MC/ARM/thumb1-relax-ldrlit.s

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
index 9230ff7baedadaf..ca3b77e4a356535 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
@@ -74,10 +74,11 @@ const MCFixupKindInfo &ARMAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
       // ARMFixupKinds.h.
       //
       // Name                      Offset (bits) Size (bits)     Flags
-      {"fixup_arm_ldst_pcrel_12", 0, 32, IsPCRelConstant},
+      {"fixup_arm_ldst_pcrel_12", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
       {"fixup_t2_ldst_pcrel_12", 0, 32,
-       IsPCRelConstant | MCFixupKindInfo::FKF_IsAlignedDownTo32Bits},
-      {"fixup_arm_pcrel_10_unscaled", 0, 32, IsPCRelConstant},
+       MCFixupKindInfo::FKF_IsPCRel |
+           MCFixupKindInfo::FKF_IsAlignedDownTo32Bits},
+      {"fixup_arm_pcrel_10_unscaled", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
       {"fixup_arm_pcrel_10", 0, 32, IsPCRelConstant},
       {"fixup_t2_pcrel_10", 0, 32,
        MCFixupKindInfo::FKF_IsPCRel |

diff  --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
index f2ca6f91477f44d..985097fc3281051 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
@@ -158,6 +158,12 @@ unsigned ARMELFObjectWriter::GetRelocTypeInner(const MCValue &Target,
       default:
         return ELF::R_ARM_THM_CALL;
       }
+    case ARM::fixup_arm_ldst_pcrel_12:
+      return ELF::R_ARM_LDR_PC_G0;
+    case ARM::fixup_arm_pcrel_10_unscaled:
+      return ELF::R_ARM_LDRS_PC_G0;
+    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-arm-ldr-imm8-relocs.s b/llvm/test/MC/ARM/pcrel-arm-ldr-imm8-relocs.s
new file mode 100644
index 000000000000000..40453d6ef341a4b
--- /dev/null
+++ b/llvm/test/MC/ARM/pcrel-arm-ldr-imm8-relocs.s
@@ -0,0 +1,42 @@
+@ RUN: llvm-mc -filetype=obj -triple=armv7 %s -o %t
+@ RUN: llvm-readelf -r %t | FileCheck %s --check-prefix=ARM
+@ RUN: llvm-objdump -d --triple=armv7 %t | FileCheck %s --check-prefix=ARM_ADDEND
+
+@ ARM: R_ARM_LDRS_PC_G0
+@ ARM: R_ARM_LDRS_PC_G0
+@ ARM: R_ARM_LDRS_PC_G0
+@ ARM: R_ARM_LDRS_PC_G0
+@ ARM: R_ARM_LDRS_PC_G0
+@ ARM: R_ARM_LDRS_PC_G0
+
+// The value format is decimal in these specific cases, but it's hex for other
+// ldr instructions. These checks are valid for both formats.
+
+@ ARM_ADDEND: r0, [pc, #-{{(0x)?}}8]
+@ ARM_ADDEND: r0, [pc, #-{{(0x)?}}8]
+@ ARM_ADDEND: r0, [pc, #-{{(0x)?}}8]
+@ ARM_ADDEND: r0, [pc, #-{{16|0x10}}]
+@ ARM_ADDEND: r0, [pc, #-{{16|0x10}}]
+@ ARM_ADDEND: r0, [pc]
+
+    .arm
+    .section .text.bar, "ax"
+    .balign 4
+    .global bar
+    .type bar, %function
+bar:
+    ldrh r0, foo
+    ldrsb r0, foo
+    ldrsh r0, foo
+    ldrh r0, just_after-8
+    ldrsb r0, just_after-8
+    ldrsh r0, foo+8
+    bx lr
+
+    .section .data.foo, "a", %progbits
+    .balign 4
+    .global foo
+foo:
+    .word 0x11223344, 0x55667788
+just_after:
+    .word 0x9900aabb, 0xccddeeff

diff  --git a/llvm/test/MC/ARM/pcrel-global.s b/llvm/test/MC/ARM/pcrel-global.s
index 91ef3b6ca7b15ac..15d46cf2063ecff 100644
--- a/llvm/test/MC/ARM/pcrel-global.s
+++ b/llvm/test/MC/ARM/pcrel-global.s
@@ -9,10 +9,9 @@
 @ DISASM-LABEL: <bar>:
 @ DISASM-NEXT:    adr.w   r0, #-4
 @ DISASM-NEXT:    adr.w   r0, #-8
-@ DISASM-NEXT:    ldr.w   pc, [pc, #-0xc]         @ 0x10 <bar>
-@ DISASM-NEXT:    ldr     r0, [pc, #0x0]          @ 0x20 <bar+0x10>
+@ DISASM-NEXT:    ldr     r0, [pc, #0x0]          @ 0x14 <bar+0xc>
 @ DISASM-NEXT:    add     r0, pc
-@ DISASM-NEXT:   .word   0xffffffef
+@ DISASM-NEXT:   .word   0xfffffff3
 @@ GNU assembler creates an R_ARM_REL32 referencing bar.
 @ DISASM-NOT:    {{.}}
 
@@ -20,10 +19,8 @@
 
 .globl foo
 foo:
-ldrd r0, r1, foo @ arm_pcrel_10_unscaled
 vldr d0, foo     @ arm_pcrel_10
 adr r2, foo      @ arm_adr_pcrel_12
-ldr r0, foo      @ arm_ldst_pcrel_12
 
 .thumb
 .thumb_func
@@ -32,7 +29,6 @@ ldr r0, foo      @ arm_ldst_pcrel_12
 bar:
 adr r0, bar      @ thumb_adr_pcrel_10
 adr.w r0, bar    @ t2_adr_pcrel_12
-ldr.w pc, bar    @ t2_ldst_pcrel_12
 
   ldr r0, .LCPI
 .LPC0_1:

diff  --git a/llvm/test/MC/ARM/pcrel-ldr-relocs.s b/llvm/test/MC/ARM/pcrel-ldr-relocs.s
new file mode 100644
index 000000000000000..120d54ebafe0876
--- /dev/null
+++ b/llvm/test/MC/ARM/pcrel-ldr-relocs.s
@@ -0,0 +1,46 @@
+@ RUN: llvm-mc -filetype=obj -triple=armv7 %s -o %t
+@ RUN: llvm-readelf -r %t | FileCheck %s --check-prefix=ARM
+@ RUN: llvm-objdump -d --triple=armv7 %t | FileCheck %s --check-prefix=ARM_ADDEND
+@ RUN: llvm-mc -filetype=obj -triple=thumbv7 %s -o %t
+@ RUN: llvm-readelf -r %t | FileCheck %s --check-prefix=THUMB
+@ RUN: llvm-objdump -d --triple=thumbv7 %t | FileCheck %s --check-prefix=THUMB_ADDEND
+
+@ ARM: R_ARM_LDR_PC_G0
+@ ARM: R_ARM_LDR_PC_G0
+@ ARM: R_ARM_LDR_PC_G0
+@ ARM: R_ARM_LDR_PC_G0
+
+@ ARM_ADDEND: r0, [pc, #-0x8]
+@ ARM_ADDEND: r0, [pc, #-0x8]
+@ ARM_ADDEND: r0, [pc, #-0x10]
+@ ARM_ADDEND: r0, [pc]
+
+@ THUMB: R_ARM_THM_PC12
+@ THUMB: R_ARM_THM_PC12
+@ THUMB: R_ARM_THM_PC12
+@ THUMB: R_ARM_THM_PC12
+
+@ THUMB_ADDEND: r0, [pc, #-0x4]
+@ THUMB_ADDEND: r0, [pc, #-0x4]
+@ THUMB_ADDEND: r0, [pc, #-0xc]
+@ THUMB_ADDEND: r0, [pc, #0x4]
+
+    .section .text.bar, "ax"
+    .balign 4
+    .global bar
+    .type bar, %function
+bar:
+    ldr r0, foo1
+    ldrb r0, foo1
+    ldr r0, foo2-8
+    ldrb r0, foo1+8
+    bx lr
+
+    .section .data.foo, "a", %progbits
+    .balign 4
+    .global foo1
+    .global foo2
+foo1:
+    .word 0x11223344, 0x55667788
+foo2:
+    .word 0x99aabbcc, 0xddeeff00

diff  --git a/llvm/test/MC/ARM/pcrel-thumb-ldr2-relocs.s b/llvm/test/MC/ARM/pcrel-thumb-ldr2-relocs.s
new file mode 100644
index 000000000000000..17ca72bd3f00cad
--- /dev/null
+++ b/llvm/test/MC/ARM/pcrel-thumb-ldr2-relocs.s
@@ -0,0 +1,41 @@
+@ RUN: llvm-mc -filetype=obj -triple=thumbv7 %s -o %t
+@ RUN: llvm-readelf -r %t | FileCheck %s --check-prefix=THUMB
+@ RUN: llvm-objdump -d --triple=thumbv7 %t | FileCheck %s --check-prefix=THUMB_ADDEND
+
+@ All the ldr variants produce a relocation
+@ THUMB: R_ARM_THM_PC12
+@ THUMB: R_ARM_THM_PC12
+@ THUMB: R_ARM_THM_PC12
+@ THUMB: R_ARM_THM_PC12
+@ THUMB: R_ARM_THM_PC12
+@ THUMB: R_ARM_THM_PC12
+
+@ THUMB_ADDEND: r0, [pc, #-0x4]
+@ THUMB_ADDEND: r0, [pc, #-0x4]
+@ THUMB_ADDEND: r0, [pc, #-0x4]
+@ THUMB_ADDEND: r0, [pc, #0x4]
+@ THUMB_ADDEND: r0, [pc, #-0xc]
+@ THUMB_ADDEND: r0, [pc, #0x4]
+
+    .thumb
+    .section .text.bar, "ax"
+    .balign 4
+    .global bar
+    .type bar, %function
+bar:
+    ldrh r0, foo1
+    ldrsb r0, foo1
+    ldrsh r0, foo1
+    ldrh r0, foo1+8
+    ldrsb r0, foo2-8
+    ldrsh r0, foo1+8
+    bx lr
+
+    .section .data.foo, "a", %progbits
+    .balign 4
+    .global foo1
+    .global foo2
+foo1:
+    .word 0x11223344, 0x55667788
+foo2:
+    .word 0x9900aabb, 0xccddeeff

diff  --git a/llvm/test/MC/ARM/thumb1-relax-ldrlit.s b/llvm/test/MC/ARM/thumb1-relax-ldrlit.s
index 5cba3690f1feb82..8f455c89d41eb06 100644
--- a/llvm/test/MC/ARM/thumb1-relax-ldrlit.s
+++ b/llvm/test/MC/ARM/thumb1-relax-ldrlit.s
@@ -1,6 +1,5 @@
 @ 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
 
         .global func1
 _func1:


        


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