[llvm] 2bfee35 - [MC][ELF] Emit a relocation if target is defined in the same section and is non-local
Fangrui Song via llvm-commits
llvm-commits at lists.llvm.org
Sun Jan 12 13:46:31 PST 2020
Author: Fangrui Song
Date: 2020-01-12T13:46:24-08:00
New Revision: 2bfee35cb860859b436de0b780fbd00d68e198a4
URL: https://github.com/llvm/llvm-project/commit/2bfee35cb860859b436de0b780fbd00d68e198a4
DIFF: https://github.com/llvm/llvm-project/commit/2bfee35cb860859b436de0b780fbd00d68e198a4.diff
LOG: [MC][ELF] Emit a relocation if target is defined in the same section and is non-local
For a target symbol defined in the same section, currently we don't emit
a relocation if VariantKind is VK_None (with few exceptions like RISC-V
relaxation), while GNU as emits one. This causes program behavior
differences with and without -ffunction-sections, and can break intended
symbol interposition in a -shared link.
```
.globl foo
foo:
call foo # no relocation. On other targets, may be written as b foo, etc
call bar # a relocation if bar is in another section (e.g. -ffunction-sections)
call foo at plt # a relocation
```
Unify these cases by always emitting a relocation. If we ever want to
optimize `call foo` in -shared links, we should emit a STB_LOCAL alias
and call via the alias.
ARM/thumb2-beq-fixup.s: we now emit a relocation to global_thumb_fn as GNU as does.
X86/Inputs/align-branch-64-2.s: we now emit R_X86_64_PLT32 to foo as GNU does.
ELF/relax.s: rewrite the test as target-in-same-section.s .
We omitted relocations to `global` and now emit R_X86_64_PLT32.
Note, GNU as does not emit a relocation for `jmp global` (maybe its own
bug). Our new behavior is compatible except `jmp global`.
Reviewed By: peter.smith
Differential Revision: https://reviews.llvm.org/D72197
Added:
llvm/test/MC/ELF/target-in-same-section.s
Modified:
lld/test/ELF/global-offset-table-position-aarch64.s
llvm/lib/MC/ELFObjectWriter.cpp
llvm/test/MC/ARM/thumb1-branch-reloc.s
llvm/test/MC/ARM/thumb2-beq-fixup.s
llvm/test/MC/X86/align-branch-64-2a.s
llvm/test/MC/X86/align-branch-64-2b.s
llvm/test/MC/X86/align-branch-64-2c.s
Removed:
llvm/test/MC/ELF/relax.s
################################################################################
diff --git a/lld/test/ELF/global-offset-table-position-aarch64.s b/lld/test/ELF/global-offset-table-position-aarch64.s
index cfe3003babe3..1a3e8062546f 100644
--- a/lld/test/ELF/global-offset-table-position-aarch64.s
+++ b/lld/test/ELF/global-offset-table-position-aarch64.s
@@ -20,7 +20,7 @@ _start:
.long _GLOBAL_OFFSET_TABLE_ - .
// CHECK: Name: _GLOBAL_OFFSET_TABLE_ (11)
-// CHECK-NEXT: Value: 0x30360
+// CHECK-NEXT: Value:
// CHECK-NEXT: Size: 0
// CHECK-NEXT: Binding: Local (0x0)
// CHECK-NEXT: Type: None (0x0)
diff --git a/llvm/lib/MC/ELFObjectWriter.cpp b/llvm/lib/MC/ELFObjectWriter.cpp
index f8e938893444..b421d0b2bf68 100644
--- a/llvm/lib/MC/ELFObjectWriter.cpp
+++ b/llvm/lib/MC/ELFObjectWriter.cpp
@@ -569,26 +569,6 @@ void ELFWriter::writeSymbol(SymbolTableWriter &Writer, uint32_t StringIndex,
IsReserved);
}
-// True if the assembler knows nothing about the final value of the symbol.
-// This doesn't cover the comdat issues, since in those cases the assembler
-// can at least know that all symbols in the section will move together.
-static bool isWeak(const MCSymbolELF &Sym) {
- if (Sym.getType() == ELF::STT_GNU_IFUNC)
- return true;
-
- switch (Sym.getBinding()) {
- default:
- llvm_unreachable("Unknown binding");
- case ELF::STB_LOCAL:
- return false;
- case ELF::STB_GLOBAL:
- return false;
- case ELF::STB_WEAK:
- case ELF::STB_GNU_UNIQUE:
- return true;
- }
-}
-
bool ELFWriter::isInSymtab(const MCAsmLayout &Layout, const MCSymbolELF &Symbol,
bool Used, bool Renamed) {
if (Symbol.isVariable()) {
@@ -1534,7 +1514,7 @@ bool ELFObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
const auto &SymA = cast<MCSymbolELF>(SA);
if (IsPCRel) {
assert(!InSet);
- if (isWeak(SymA))
+ if (SymA.getBinding() != ELF::STB_LOCAL)
return false;
}
return MCObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
diff --git a/llvm/test/MC/ARM/thumb1-branch-reloc.s b/llvm/test/MC/ARM/thumb1-branch-reloc.s
index c599389d1c2d..22384bec0274 100644
--- a/llvm/test/MC/ARM/thumb1-branch-reloc.s
+++ b/llvm/test/MC/ARM/thumb1-branch-reloc.s
@@ -18,4 +18,14 @@
@CHECK: Section {{.*}} .rel.text.cond {
@CHECK: 0x0 R_ARM_THM_JUMP8
@CHECK: }
-
\ No newline at end of file
+
+ .section .text.insection
+.globl global
+local:
+global:
+ b local
+ b global
+
+ at CHECK: Section {{.*}} .rel.text.insection {
+ at CHECK-NEXT: 0x2 R_ARM_THM_JUMP11 global 0x0
+ at CHECK-NEXT: }
diff --git a/llvm/test/MC/ARM/thumb2-beq-fixup.s b/llvm/test/MC/ARM/thumb2-beq-fixup.s
index e6d43e8fed96..36728081162f 100644
--- a/llvm/test/MC/ARM/thumb2-beq-fixup.s
+++ b/llvm/test/MC/ARM/thumb2-beq-fixup.s
@@ -36,4 +36,5 @@ global_thumb_fn:
@ CHECK: Section (3) .rel.text
@ CHECK-NEXT: 0x0 R_ARM_THM_JUMP19 internal_arm_fn 0x0
@ CHECK-NEXT: 0x4 R_ARM_THM_JUMP19 global_arm_fn 0x0
+@ CHECK-NEXT: 0x8 R_ARM_THM_JUMP19 global_thumb_fn 0x0
@ CHECK-NEXT: }
diff --git a/llvm/test/MC/ELF/relax.s b/llvm/test/MC/ELF/relax.s
deleted file mode 100644
index 27de52963bad..000000000000
--- a/llvm/test/MC/ELF/relax.s
+++ /dev/null
@@ -1,33 +0,0 @@
-// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | llvm-readobj -S --sd --symbols | FileCheck %s
-
-// Test that we do not relax these.
-
-bar:
-.globl foo
-foo:
- .set zed,foo
-
- jmp bar
- jmp foo
- jmp zed
-
-// CHECK: Section {
-// CHECK: Name: .text
-// CHECK-NEXT: Type: SHT_PROGBITS
-// CHECK-NEXT: Flags [
-// CHECK-NEXT: SHF_ALLOC
-// CHECK-NEXT: SHF_EXECINSTR
-// CHECK-NEXT: ]
-// CHECK-NEXT: Address: 0x0
-// CHECK-NEXT: Offset: 0x40
-// CHECK-NEXT: Size: 6
-// CHECK-NEXT: Link: 0
-// CHECK-NEXT: Info: 0
-// CHECK-NEXT: AddressAlignment: 4
-// CHECK-NEXT: EntrySize: 0
-// CHECK-NEXT: SectionData (
-// CHECK-NEXT: 0000: EBFEEBFC EBFA
-// CHECK-NEXT: )
-// CHECK-NEXT: }
-// CHECK: Symbol {
-// CHECK: Name: foo
diff --git a/llvm/test/MC/ELF/target-in-same-section.s b/llvm/test/MC/ELF/target-in-same-section.s
new file mode 100644
index 000000000000..dbdacaffdb7f
--- /dev/null
+++ b/llvm/test/MC/ELF/target-in-same-section.s
@@ -0,0 +1,39 @@
+## For a target defined in the same section, create a relocation if the
+## symbol is not local, otherwise resolve the fixup statically.
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %s -o %t
+# RUN: llvm-readobj -r %t | FileCheck --check-prefix=RELOC %s
+# RUN: llvm-objdump -d --no-show-raw-insn %t | FileCheck %s
+
+# RELOC: .rela.text {
+# RELOC-NEXT: 0x5 R_X86_64_PLT32 global 0xFFFFFFFFFFFFFFFC
+# RELOC-NEXT: 0xA R_X86_64_PLT32 weak 0xFFFFFFFFFFFFFFFC
+# RELOC-NEXT: 0x19 R_X86_64_PLT32 global 0xFFFFFFFFFFFFFFFC
+# RELOC-NEXT: 0x1E R_X86_64_PLT32 weak 0xFFFFFFFFFFFFFFFC
+# RELOC-NEXT: }
+
+# CHECK: 0: jmp
+# CHECK-NEXT: 2: jmp
+# CHECK-NEXT: 4: jmp
+# CHECK-NEXT: 9: jmp
+# CHECK-NEXT: e: callq
+# CHECK-NEXT: 13: callq
+# CHECK-NEXT: 18: callq
+# CHECK-NEXT: 1d: callq
+# CHECK-NEXT: 22: retq
+
+.globl global
+.weak weak
+global:
+weak:
+local:
+.set var,global
+ jmp var
+ jmp local
+ jmp global
+ jmp weak
+
+ call var
+ call local
+ call global
+ call weak
+ ret
diff --git a/llvm/test/MC/X86/align-branch-64-2a.s b/llvm/test/MC/X86/align-branch-64-2a.s
index 61e9e1f899b9..0652840cbc29 100644
--- a/llvm/test/MC/X86/align-branch-64-2a.s
+++ b/llvm/test/MC/X86/align-branch-64-2a.s
@@ -12,6 +12,6 @@
# CHECK-NEXT: 3e: ff d0 callq *%rax
# CHECK-COUNT-3: : 64 89 04 25 01 00 00 00 movl %eax, %fs:1
# CHECK-NEXT: 58: 55 pushq %rbp
-# CHECK-NEXT: 59: e8 a2 ff ff ff callq {{.*}}
+# CHECK-NEXT: 59: e8 00 00 00 00 callq {{.*}}
# CHECK-COUNT-4: : 64 89 04 25 01 00 00 00 movl %eax, %fs:1
# CHECK: 7e: ff 14 25 00 00 00 00 callq *0
diff --git a/llvm/test/MC/X86/align-branch-64-2b.s b/llvm/test/MC/X86/align-branch-64-2b.s
index 1cb49f7d1090..91494fa36ba3 100644
--- a/llvm/test/MC/X86/align-branch-64-2b.s
+++ b/llvm/test/MC/X86/align-branch-64-2b.s
@@ -11,7 +11,7 @@
# CHECK-NEXT: 3c: ff d0 callq *%rax
# CHECK-COUNT-3: : 64 89 04 25 01 00 00 00 movl %eax, %fs:1
# CHECK: 56: 55 pushq %rbp
-# CHECK-NEXT: 57: e8 a4 ff ff ff callq {{.*}}
+# CHECK-NEXT: 57: e8 00 00 00 00 callq {{.*}}
# CHECK-COUNT-4: : 64 89 04 25 01 00 00 00 movl %eax, %fs:1
# CHECK-COUNT-4: : 90 nop
# CHECK: 80: ff 14 25 00 00 00 00 callq *0
diff --git a/llvm/test/MC/X86/align-branch-64-2c.s b/llvm/test/MC/X86/align-branch-64-2c.s
index bb750aa24a07..6754feb85f2f 100644
--- a/llvm/test/MC/X86/align-branch-64-2c.s
+++ b/llvm/test/MC/X86/align-branch-64-2c.s
@@ -14,6 +14,6 @@
# CHECK-COUNT-3: : 64 89 04 25 01 00 00 00 movl %eax, %fs:1
# CHECK: 5a: 55 pushq %rbp
# CHECK-COUNT-5: : 90 nop
-# CHECK: 60: e8 9b ff ff ff callq {{.*}}
+# CHECK: 60: e8 00 00 00 00 callq {{.*}}
# CHECK-COUNT-4: : 64 89 04 25 01 00 00 00 movl %eax, %fs:1
# CHECK: 85: ff 14 25 00 00 00 00 callq *0
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