[CHERIoT] Make sure that CAPALIGN directives work properly with ". += ..." directives.

Author: resistor

lld/ELF/LinkerScript.cpp

@@ -1102,12 +1102,21 @@ void LinkerScript::diagnoseMissingSGSectionAddress() const {
 // This is roughly the same logic as the loop in assignOffsets() to loop
 // through all commands and input sections in an output section to calculate
 // the total size.
-static uint64_t outputSectionCheriAlignment(Ctx &ctx, OutputSection *sec)
-{
+uint64_t LinkerScript::outputSectionCheriAlignment(OutputSection *sec) {
   uint64_t total = 0;
 
   for (SectionCommand *cmd : sec->commands) {
-    if (dyn_cast<SymbolAssignment>(cmd)) {
+    if (SymbolAssignment *assign = dyn_cast<SymbolAssignment>(cmd)) {
+      if (assign->name == ".") {
+        // Evaluating an expression like ". += 0x100" will attempt to read
+        // the current value of dot, which isn't accurate since we're doing
+        // things out of order here. We can fake it by temporarily setting
+        // the value of dot and restoring it later.
+        auto oldDot = dot;
+        dot = total;
+        total += assign->expression().getValue();
+        dot = oldDot;
+      }
       continue;
     }
 
@@ -1230,7 +1239,7 @@ bool LinkerScript::assignOffsets(OutputSection *sec) {
     // ALIGN is respected. sec->alignment is the max of ALIGN and the maximum of
     // input section alignments.
     if (sec->isCapAligned) {
-      uint64_t capAlignment = outputSectionCheriAlignment(ctx, sec);
+      uint64_t capAlignment = outputSectionCheriAlignment(sec);
       if (capAlignment > 1) {
         sec->addralign = std::max<uint64_t>(capAlignment, sec->addralign);
       }

lld/ELF/LinkerScript.h

@@ -340,6 +340,7 @@ class LinkerScript final {
   findMemoryRegion(OutputSection *sec, MemoryRegion *hint);
 
   bool assignOffsets(OutputSection *sec);
+  uint64_t outputSectionCheriAlignment(OutputSection *sec);
 
   // This captures the local AddressState and makes it accessible
   // deliberately. This is needed as there are some cases where we cannot just

lld/test/ELF/cheri/Inputs/cheriot-capalign.lds

@@ -0,0 +1,9 @@
+SECTIONS {
+  . = 0x1245;
+  . = ALIGN(8);
+  .bar : CAPALIGN {
+    .bar_start = .;
+	  . += 0x100000;
+	  .bar_end = .;
+  }
+}

lld/test/ELF/cheri/cheriot-capalign.s

@@ -0,0 +1,23 @@
+// REQUIRES: riscv
+// RUN: llvm-mc -triple riscv32-unknown-cheriotrtos -filetype=obj -o %t %s
+// RUN: ld.lld %t %S/Inputs/cheriot-capalign.lds -o %t2
+// RUN: llvm-readobj --sections %t2 | FileCheck %s
+
+// Verify that CAPALIGN directives in the linker script actually
+// force higher alignment on an over-sized section.
+
+// CHECK:          Index: 2
+// CHECK-NEXT:     Name: .bar (7)
+// CHECK-NEXT:     Type: SHT_PROGBITS (0x1)
+// CHECK-NEXT:     Flags [ (0x0)
+// CHECK-NEXT:     ]
+// CHECK-NEXT:     Address: 0x0
+// CHECK-NEXT:     Offset: 0x20000
+// CHECK-NEXT:     Size: 1179648
+// CHECK-NEXT:     Link: 0
+// CHECK-NEXT:     Info: 0
+// CHECK-NEXT:     AddressAlignment: 131072
+// CHECK-NEXT:     EntrySize: 0
+
+.section .bar
+.byte 0