[ELF] Allow specifying the stack size

[phosek]

Summary

This option can be used to set the size of the initial stack by setting the size of the PT_GNU_STACK segment.

[ruiu]

LGTM with nits.

ELF/Config.h

117

Sort.

ELF/Driver.cpp

260

getZOptionValue would be a better name because this function returns a value.

264–265

You can merge the two ifs.

413

Nit: remove {}.

test/ELF/zstack-size.s

11–47

These program headers are not relevant, so please remove.

[phosek]

ELF/Config.h

117

Isn't this already sorted (relative to other Z fields)?

[ruiu]

LGTM wtih this change.

ELF/Config.h

117

But other members are sorted by type, too. See ImageBase below.

[phosek]

ELF/Config.h

117

I missed the sorting by type.

ELF/Config.h

   bool ZNow;
   bool ZOrigin;
   bool ZRelro;
+  uint64_t ZStackSize = -1;
   UnresolvedPolicy UnresolvedSymbols;
   BuildIdKind BuildId = BuildIdKind::None;
   ELFKind EKind = ELFNoneKind;

ELF/Driver.cpp

   return false;
 }
 
+static Optional<StringRef>
+hasZOptionValue(opt::InputArgList &Args, StringRef Key) {
+  for (auto *Arg : Args.filtered(OPT_z)) {
+    StringRef Value = Arg->getValue();
+    size_t Pos = Value.find("=");
+    if (Pos != StringRef::npos) {
+      if (Key == Value.substr(0, Pos))
+        return Value.substr(Pos + 1);
+    }
+  }
+  return None;
+}
+
 void LinkerDriver::main(ArrayRef<const char *> ArgsArr) {
   ELFOptTable Parser;
   opt::InputArgList Args = Parser.parse(ArgsArr.slice(1));

   Config->ZOrigin = hasZOption(Args, "origin");
   Config->ZRelro = !hasZOption(Args, "norelro");
 
+  if (Optional<StringRef> Value = hasZOptionValue(Args, "stack-size")) {
+    if (Value->getAsInteger(0, Config->ZStackSize))
+      error("invalid stack size: " + *Value);
+  }
+
   if (Config->Relocatable)
     Config->StripAll = false;
 

ELF/Writer.cpp

 
   // PT_GNU_STACK is a special section to tell the loader to make the
   // pages for the stack non-executable.
-  if (!Config->ZExecStack)
-    AddHdr(PT_GNU_STACK, PF_R | PF_W);
+  if (!Config->ZExecStack) {
+    Phdr &Hdr = *AddHdr(PT_GNU_STACK, PF_R | PF_W);
+    if (Config->ZStackSize != uint64_t(-1))
+      Hdr.H.p_memsz = Config->ZStackSize;
+  }
 
   if (Note.First)
     Ret.push_back(std::move(Note));

test/ELF/zstack-size.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: ld.lld -z stack-size=0x1000 %t -o %t1
+# RUN: llvm-readobj -program-headers %t1 | FileCheck %s
+
+.global _start
+_start:
+  nop
+
+# CHECK:      ProgramHeaders [
+# CHECK-NEXT:   ProgramHeader {
+# CHECK-NEXT:     Type: PT_PHDR (0x6)
+# CHECK-NEXT:     Offset: 0x40
+# CHECK-NEXT:     VirtualAddress: 0x10040
+# CHECK-NEXT:     PhysicalAddress: 0x10040
+# CHECK-NEXT:     FileSize: 224
+# CHECK-NEXT:     MemSize: 224
+# CHECK-NEXT:     Flags [ (0x4)
+# CHECK-NEXT:       PF_R (0x4)
+# CHECK-NEXT:     ]
+# CHECK-NEXT:     Alignment: 8
+# CHECK-NEXT:   }
+# CHECK-NEXT:   ProgramHeader {
+# CHECK-NEXT:     Type: PT_LOAD (0x1)
+# CHECK-NEXT:     Offset: 0x0
+# CHECK-NEXT:     VirtualAddress: 0x10000
+# CHECK-NEXT:     PhysicalAddress: 0x10000
+# CHECK-NEXT:     FileSize: 288
+# CHECK-NEXT:     MemSize: 288
+# CHECK-NEXT:     Flags [ (0x4)
+# CHECK-NEXT:       PF_R (0x4)
+# CHECK-NEXT:     ]
+# CHECK-NEXT:     Alignment: 4096
+# CHECK-NEXT:   }
+# CHECK-NEXT:   ProgramHeader {
+# CHECK-NEXT:     Type: PT_LOAD (0x1)
+# CHECK-NEXT:     Offset: 0x1000
+# CHECK-NEXT:     VirtualAddress: 0x11000
+# CHECK-NEXT:     PhysicalAddress: 0x11000
+# CHECK-NEXT:     FileSize: 1
+# CHECK-NEXT:     MemSize: 1
+# CHECK-NEXT:     Flags [ (0x5)
+# CHECK-NEXT:       PF_R (0x4)
+# CHECK-NEXT:       PF_X (0x1)
+# CHECK-NEXT:     ]
+# CHECK-NEXT:     Alignment: 4096
+# CHECK-NEXT:   }
+# CHECK-NEXT:   ProgramHeader {
+# CHECK-NEXT:     Type: PT_GNU_STACK (0x6474E551)
+# CHECK-NEXT:     Offset: 0x0
+# CHECK-NEXT:     VirtualAddress: 0x0
+# CHECK-NEXT:     PhysicalAddress: 0x0
+# CHECK-NEXT:     FileSize: 0
+# CHECK-NEXT:     MemSize: 4096
+# CHECK-NEXT:     Flags [ (0x6)
+# CHECK-NEXT:       PF_R (0x4)
+# CHECK-NEXT:       PF_W (0x2)
+# CHECK-NEXT:     ]
+# CHECK-NEXT:     Alignment: 0
+# CHECK-NEXT:   }