[ELF][CHERI] Support emitting IRELATIVE-style caprelocs

Author: jrtc27

lld/ELF/Arch/Cheri.cpp

@@ -318,6 +318,8 @@ struct CaptablePermissions {
                                    << ((sizeof(typename ELFT::uint) * 8) - 1);
   static const uint64_t readOnly = UINT64_C(1)
                                    << ((sizeof(typename ELFT::uint) * 8) - 2);
+  static const uint64_t indirect = UINT64_C(1)
+                                   << ((sizeof(typename ELFT::uint) * 8) - 3);
 };
 
 template <class ELFT>
@@ -349,32 +351,30 @@ void CheriCapRelocsSection::writeToImpl(uint8_t *buf) {
 
     // The target VA is the base address of the capability, so symbol + 0
     uint64_t targetVA;
-    bool isFunc, isTls;
+    bool isFunc, isGnuIFunc, isTls;
     OutputSection *os;
     if (Symbol *s = dyn_cast<Symbol *>(realTarget.symOrSec)) {
-      if (s->isGnuIFunc())
-        error("cannot reference non-preemptible IFUNC as a capability, "
-              "needed for symbol " +
-              verboseToString(ctx, s) + "\n>>> referenced by " +
-              location.toString(ctx));
-
       targetVA = realTarget.sym()->getVA(ctx, 0);
       isFunc = s->isFunc();
+      isGnuIFunc = s->isGnuIFunc();
       isTls = s->isTls();
       os = s->getOutputSection();
     } else {
       InputSectionBase *isec = cast<InputSectionBase *>(realTarget.symOrSec);
       targetVA = isec->getVA(0);
       isFunc = (isec->flags & SHF_EXECINSTR) != 0;
+      isGnuIFunc = false;
       isTls = isec->type == STT_TLS;
       os = isec->getOutputSection();
     }
     uint64_t targetSize = getTargetSize(ctx, location, realTarget);
     uint64_t targetOffset = reloc.capabilityOffset + realTarget.offset;
     uint64_t permissions = 0;
     // Fow now Function implies ReadOnly so don't add the flag
-    if (isFunc) {
+    if (isFunc || isGnuIFunc) {
       permissions |= CaptablePermissions<ELFT>::function;
+      if (isGnuIFunc)
+        permissions |= CaptablePermissions<ELFT>::indirect;
     } else if (os) {
       assert(!isTls);
       // if ((OS->getPhdrFlags() & PF_W) == 0) {

lld/test/ELF/cheri/riscv/ifunc-nonpreemptible.s

@@ -0,0 +1,72 @@
+# REQUIRES: riscv
+# RUN: %riscv32_cheri_purecap_llvm-mc -filetype=obj %s -o %t.32.o
+# RUN: ld.lld %t.32.o -z separate-code -o %t.32
+# RUN: llvm-readobj -r --cap-relocs -x .got.plt %t.32 | FileCheck --check-prefix=RELOC32 %s
+# RUN: llvm-readelf -x .got.plt %t.32 | FileCheck --check-prefix=GOTPLT32 %s
+# RUN: llvm-readelf -S -s %t.32 | FileCheck --check-prefixes=SEC,NM %s
+# RUN: llvm-objdump -d --no-show-raw-insn %t.32 | FileCheck --check-prefixes=DIS,DIS32 %s
+
+# RUN: %riscv64_cheri_purecap_llvm-mc -filetype=obj %s -o %t.64.o
+# RUN: ld.lld %t.64.o -z separate-code -o %t.64
+# RUN: llvm-readelf -S -s %t.64 | FileCheck --check-prefixes=SEC,NM %s
+# RUN: llvm-readobj -r --cap-relocs -x .got.plt %t.64 | FileCheck --check-prefix=RELOC64 %s
+# RUN: llvm-readelf -x .got.plt %t.64 | FileCheck --check-prefix=GOTPLT64 %s
+# RUN: llvm-objdump -d --no-show-raw-insn %t.64 | FileCheck --check-prefixes=DIS,DIS64 %s
+
+# SEC: .iplt PROGBITS {{0*}}00011010
+
+## Canonical PLT in .iplt
+# NM: {{0*}}00011010 16 FUNC GLOBAL DEFAULT {{.*}} func
+
+# RELOC32:      Relocations [
+# RELOC32-NEXT: ]
+# RELOC32:      CHERI __cap_relocs [
+# RELOC32-NEXT:   0x012000 (fptr) Base: 0x11010 (func+0) Length: 16 Perms: Function
+# RELOC32-NEXT:   0x012008 Base: 0x11000 ($x+0) Length: 4 Perms: GNU Indirect Function
+# RELOC32-NEXT: ]
+# GOTPLT32:      section '.got.plt':
+# GOTPLT32-NEXT: 0x00012008 00000000 00000000
+
+# RELOC64:      Relocations [
+# RELOC64-NEXT: ]
+# RELOC64:      CHERI __cap_relocs [
+# RELOC64-NEXT:   0x012000 (fptr) Base: 0x11010 (func+0) Length: 16 Perms: Function
+# RELOC64-NEXT:   0x012010 Base: 0x11000 ($x+0) Length: 4 Perms: GNU Indirect Function
+# RELOC64-NEXT: ]
+# GOTPLT64:      section '.got.plt':
+# GOTPLT64-NEXT: 0x00012010 00000000 00000000 00000000 00000000
+
+# DIS:      <_start>:
+## func - . = 0x11010-0x11004 = 12
+# DIS-NEXT: 11004: auipcc a0, 0
+# DIS-NEXT:        cincoffset a0, a0, 0xc
+
+# DIS:      Disassembly of section .iplt:
+# DIS:      <func>:
+## 32-bit: &.got.plt[func]-. = 0x12008-0x11010 = 4096*1-8
+## 64-bit: &.got.plt[func]-. = 0x12010-0x11010 = 4096*1+0
+# DIS-NEXT: 11010: auipcc t3, 0x1
+# DIS32-NEXT:      lc t3, -0x8(t3)
+# DIS64-NEXT:      lc t3, 0x0(t3)
+# DIS-NEXT:        jalr t1, t3
+# DIS-NEXT:        nop
+
+.text
+.globl func
+.type func, @gnu_indirect_function
+func:
+  cret
+  .size func, . - func
+
+.globl _start
+.type _start, @function
+_start:
+  cllc ca0, func
+  .size _start, . - _start
+
+.data
+.globl fptr
+.type fptr, @object
+fptr:
+  .chericap func
+  .size fptr, . - fptr