[LLD][ELF][AArch64] Mark .plt and .iplt with PURECODE flag

[Il-Capitano]

Mark the synthetic sections .plt and .iplt with the SHF_AARCH64_PURECODE section flag, allowing them to be placed in an executable-only segment.

[llvmbot]

@llvm/pr-subscribers-lld-elf

@llvm/pr-subscribers-lld

Author: Csanád Hajdú (Il-Capitano)

Changes

Mark the synthetic sections .plt and .iplt with the SHF_AARCH64_PURECODE section flag, allowing them to be placed in an executable-only segment.

---

Full diff: https://github.com/llvm/llvm-project/pull/134798.diff

3 Files Affected:

• (modified) lld/ELF/SyntheticSections.cpp (+10)
• (modified) lld/test/ELF/aarch64-gnu-ifunc-plt.s (+18-2)
• (modified) lld/test/ELF/aarch64-plt.s (+2)

diff --git a/lld/ELF/SyntheticSections.cpp b/lld/ELF/SyntheticSections.cpp
index 3bb9815336a7c..88e2a369000e1 100644
--- a/lld/ELF/SyntheticSections.cpp
+++ b/lld/ELF/SyntheticSections.cpp
@@ -2610,6 +2610,11 @@ PltSection::PltSection(Ctx &ctx)
   // modify the instructions in the PLT entries.
   if (ctx.arg.emachine == EM_SPARCV9)
     this->flags |= SHF_WRITE;
+
+  // On AArch64, PLT entries only do loads from the .got.plt section, so the
+  // .plt section can be marked with the SHF_AARCH64_PURECODE section flag.
+  if (ctx.arg.emachine == EM_AARCH64)
+    this->flags |= SHF_AARCH64_PURECODE;
 }
 
 void PltSection::writeTo(uint8_t *buf) {
@@ -2658,6 +2663,11 @@ IpltSection::IpltSection(Ctx &ctx)
     name = ".glink";
     addralign = 4;
   }
+
+  // On AArch64, PLT entries only do loads from the .got.plt section, so the
+  // .iplt section can be marked with the SHF_AARCH64_PURECODE section flag.
+  if (ctx.arg.emachine == EM_AARCH64)
+    this->flags |= SHF_AARCH64_PURECODE;
 }
 
 void IpltSection::writeTo(uint8_t *buf) {
diff --git a/lld/test/ELF/aarch64-gnu-ifunc-plt.s b/lld/test/ELF/aarch64-gnu-ifunc-plt.s
index bde6f1420540f..dfecb5c9e6ea1 100644
--- a/lld/test/ELF/aarch64-gnu-ifunc-plt.s
+++ b/lld/test/ELF/aarch64-gnu-ifunc-plt.s
@@ -5,7 +5,7 @@
 // RUN: ld.lld --hash-style=sysv %t.so %t.o -o %tout
 // RUN: llvm-objdump --no-print-imm-hex -d --no-show-raw-insn %tout | FileCheck %s --check-prefix=DISASM
 // RUN: llvm-objdump -s %tout | FileCheck %s --check-prefix=GOTPLT
-// RUN: llvm-readobj --dynamic-table -r %tout | FileCheck %s
+// RUN: llvm-readobj --dynamic-table -r -S %tout | FileCheck %s
 
 // RUN: llvm-mc -filetype=obj -triple=aarch64_be %S/Inputs/shared2.s -o %t1.be.o
 // RUN: ld.lld %t1.be.o --shared --soname=t.so -o %t.be.so
@@ -13,7 +13,23 @@
 // RUN: ld.lld --hash-style=sysv %t.be.so %t.be.o -o %t.be
 // RUN: llvm-objdump --no-print-imm-hex -d --no-show-raw-insn %t.be | FileCheck %s --check-prefix=DISASM
 // RUN: llvm-objdump -s %t.be | FileCheck %s --check-prefix=GOTPLT_BE
-// RUN: llvm-readobj --dynamic-table -r %t.be | FileCheck %s
+// RUN: llvm-readobj --dynamic-table -r -S %t.be | FileCheck %s
+
+// Check that the .iplt section has the SHF_AARCH64_PURECODE section flag set
+// CHECK:      Sections [
+// CHECK:        Name: .iplt
+// CHECK-NEXT:   Type: SHT_PROGBITS
+// CHECK-NEXT:   Flags [
+// CHECK-NEXT:     SHF_AARCH64_PURECODE
+// CHECK-NEXT:     SHF_ALLOC
+// CHECK-NEXT:     SHF_EXECINSTR
+// CHECK-NEXT:   ]
+// CHECK-NEXT:   Address: 0x210330
+// CHECK-NEXT:   Offset:
+// CHECK-NEXT:   Size: 32
+// CHECK-NEXT:   Link:
+// CHECK-NEXT:   Info:
+// CHECK-NEXT:   AddressAlignment: 16
 
 // Check that the PLTRELSZ tag does not include the IRELATIVE relocations
 // CHECK: DynamicSection [
diff --git a/lld/test/ELF/aarch64-plt.s b/lld/test/ELF/aarch64-plt.s
index 7d83a40dfc278..88e719484921b 100644
--- a/lld/test/ELF/aarch64-plt.s
+++ b/lld/test/ELF/aarch64-plt.s
@@ -14,6 +14,7 @@
 // CHECKDSO:     Name: .plt
 // CHECKDSO-NEXT:     Type: SHT_PROGBITS
 // CHECKDSO-NEXT:     Flags [
+// CHECKDSO-NEXT:       SHF_AARCH64_PURECODE
 // CHECKDSO-NEXT:       SHF_ALLOC
 // CHECKDSO-NEXT:       SHF_EXECINSTR
 // CHECKDSO-NEXT:     ]
@@ -109,6 +110,7 @@
 // CHECKEXE:     Name: .plt
 // CHECKEXE-NEXT:     Type: SHT_PROGBITS
 // CHECKEXE-NEXT:     Flags [
+// CHECKEXE-NEXT:       SHF_AARCH64_PURECODE
 // CHECKEXE-NEXT:       SHF_ALLOC
 // CHECKEXE-NEXT:       SHF_EXECINSTR
 // CHECKEXE-NEXT:     ]

[Il-Capitano]

Thanks for the approval, I'll merge this once CI is all green.

[smithp35]

Changes LGTM on my side. I don't have any suggestions to add to MaskRay's.