[CHERIoT] Use the CompressedCap tables to compute cap alignment in LLD.

Author: resistor

lld/ELF/Arch/RISCV.cpp

@@ -13,6 +13,7 @@
 #include "Symbols.h"
 #include "SyntheticSections.h"
 #include "Target.h"
+#include "llvm/CHERI/CompressedCapability.h"
 #include "llvm/Support/ELFAttributes.h"
 #include "llvm/Support/LEB128.h"
 #include "llvm/Support/RISCVAttributeParser.h"
@@ -760,16 +761,14 @@ static void tlsdescToLe(uint8_t *loc, const Relocation &rel, uint64_t val) {
 }
 
 uint64_t RISCV::cheriRequiredAlignment(uint64_t size) const {
-  // FIXME: Non-CherIoT targets will have different calculations here
-  uint64_t mantissaWidth = 9;
-  auto mantissaWidthMinusOneMask = (uint64_t(1) << (mantissaWidth - 1)) - 1;
-  uint64_t msbIdxPlusOne = 64 - llvm::countl_zero(size);
-  uint64_t e = std::max<int64_t>(int64_t(msbIdxPlusOne) - mantissaWidth, 0);
-  // If we are very close to the top, then we need to round up one more
-  if (((size >> (e + 1)) & mantissaWidthMinusOneMask) ==
-      mantissaWidthMinusOneMask)
-    ++e;
-  return uint64_t(1) << e;
+  auto CapFormat = llvm::CompressedCapability::Cheri128;
+  if (ctx.arg.isCheriot)
+    CapFormat = llvm::CompressedCapability::Cheriot64;
+  else if (!ctx.arg.is64)
+    CapFormat = llvm::CompressedCapability::Cheri64;
+
+  return llvm::CompressedCapability::GetRequiredAlignment(size, CapFormat)
+      .value();
 }
 
 void RISCV::relocateAlloc(InputSectionBase &sec, uint8_t *buf) const {

lld/ELF/Config.h

@@ -549,6 +549,9 @@ struct Config {
   // True if we are creating a pure-capability CheriABI output.
   bool isCheriAbi = false;
 
+  // True if we are creating a CHERIoT output.
+  bool isCheriot = false;
+
   // Mode of MTE to write to the ELF note. Should be one of NT_MEMTAG_ASYNC (for
   // async), NT_MEMTAG_SYNC (for sync), or NT_MEMTAG_LEVEL_NONE (for none). If
   // async or sync is enabled, write the ELF note specifying the default MTE

lld/ELF/Driver.cpp

@@ -3496,6 +3496,9 @@ template <class ELFT> void LinkerDriver::link(opt::InputArgList &args) {
 
   ctx.arg.eflags = ctx.target->calcEFlags();
   ctx.arg.isCheriAbi = ctx.target->calcIsCheriAbi();
+  if (ctx.arg.isCheriAbi)
+    ctx.arg.isCheriot = ctx.arg.eflags & EF_RISCV_CHERIOT;
+
   // maxPageSize (sometimes called abi page size) is the maximum page size that
   // the output can be run on. For example if the OS can use 4k or 64k page
   // sizes then maxPageSize must be 64k for the output to be useable on both.

llvm/include/llvm/CHERI/CompressedCapability.h

@@ -9,10 +9,14 @@
 #ifndef LLVM_COMPRESSED_CAPABILITY_H
 #define LLVM_COMPRESSED_CAPABILITY_H
 
+#include "llvm/MC/MCTargetOptions.h"
+#include "llvm/Support/Alignment.h"
+
 #include <algorithm>
 #include <cstdint>
 
 namespace llvm {
+
 namespace CompressedCapability {
 
 enum class CapabilityFormat {