[lld] a6d6734 - [lld-macho][nfc] define command UNWIND_MODE_MASK for convenience and rewrite mode-mask checking logic for clarity

[Vy Nguyen via llvm-commits]

Author: Vy Nguyen
Date: 2022-10-14T15:16:40-04:00
New Revision: a6d6734a41f4960bf7447db4515e2acfd187fea0

URL: https://github.com/llvm/llvm-project/commit/a6d6734a41f4960bf7447db4515e2acfd187fea0
DIFF: https://github.com/llvm/llvm-project/commit/a6d6734a41f4960bf7447db4515e2acfd187fea0.diff

LOG: [lld-macho][nfc] define command UNWIND_MODE_MASK for convenience and rewrite mode-mask checking logic for clarity

The previous form is currently "harmless" and happened to work but may not in the future:

Consider the struct: (for x86-64, but same issue can be said for the ARM/64 families):

```
UNWIND_X86_64_MODE_MASK                    = 0x0F000000,
UNWIND_X86_64_MODE_RBP_FRAME               = 0x01000000,
UNWIND_X86_64_MODE_STACK_IMMD              = 0x02000000,
UNWIND_X86_64_MODE_STACK_IND               = 0x03000000,
UNWIND_X86_64_MODE_DWARF                   = 0x04000000,
```

Previously, we were doing: `(encoding & MODE_DWARF) == MODE_DWARF`

As soon as a new `UNWIND_X86_64_MODE_FOO = 0x05000000` is defined, then the check above would always return true for encoding=MODE_FOO (because `(0b0101 & 0b0100) == 0b0100` )

Differential Revision: https://reviews.llvm.org/D135359

Added: 
    

Modified: 
    lld/MachO/InputFiles.cpp
    lld/MachO/Target.h
    lld/MachO/UnwindInfoSection.cpp

Removed: 
    


################################################################################
diff  --git a/lld/MachO/InputFiles.cpp b/lld/MachO/InputFiles.cpp
index 9c2051e49495c..afd0e28a3dce4 100644
--- a/lld/MachO/InputFiles.cpp
+++ b/lld/MachO/InputFiles.cpp
@@ -1096,7 +1096,8 @@ void ObjFile::registerCompactUnwind(Section &compactUnwindSection) {
     // llvm-mc omits CU entries for functions that need DWARF encoding, but
     // `ld -r` doesn't. We can ignore them because we will re-synthesize these
     // CU entries from the DWARF info during the output phase.
-    if ((encoding & target->modeDwarfEncoding) == target->modeDwarfEncoding)
+    if ((encoding & static_cast<uint32_t>(UNWIND_MODE_MASK)) ==
+        target->modeDwarfEncoding)
       continue;
 
     ConcatInputSection *referentIsec;

diff  --git a/lld/MachO/Target.h b/lld/MachO/Target.h
index 42c1142db6e1b..44a85521ace31 100644
--- a/lld/MachO/Target.h
+++ b/lld/MachO/Target.h
@@ -20,6 +20,8 @@
 #include <cstddef>
 #include <cstdint>
 
+#include "mach-o/compact_unwind_encoding.h"
+
 namespace lld::macho {
 LLVM_ENABLE_BITMASK_ENUMS_IN_NAMESPACE();
 
@@ -29,6 +31,15 @@ class DylibSymbol;
 class InputSection;
 class ObjFile;
 
+static_assert(static_cast<uint32_t>(UNWIND_X86_64_MODE_MASK) ==
+                  static_cast<uint32_t>(UNWIND_X86_MODE_MASK) &&
+              static_cast<uint32_t>(UNWIND_ARM64_MODE_MASK) ==
+                  static_cast<uint32_t>(UNWIND_X86_64_MODE_MASK));
+
+// Since the mode masks have the same value on all targets, define
+// a common one for convenience.
+constexpr uint32_t UNWIND_MODE_MASK = UNWIND_X86_64_MODE_MASK;
+
 class TargetInfo {
 public:
   template <class LP> TargetInfo(LP) {

diff  --git a/lld/MachO/UnwindInfoSection.cpp b/lld/MachO/UnwindInfoSection.cpp
index fa6f81d207357..610d8793d60ce 100644
--- a/lld/MachO/UnwindInfoSection.cpp
+++ b/lld/MachO/UnwindInfoSection.cpp
@@ -418,12 +418,10 @@ static bool canFoldEncoding(compact_unwind_encoding_t encoding) {
   // of the unwind info's unwind address, two functions that have identical
   // unwind info can't be folded if it's using this encoding since both
   // entries need unique addresses.
-  static_assert(static_cast<uint32_t>(UNWIND_X86_64_MODE_MASK) ==
-                static_cast<uint32_t>(UNWIND_X86_MODE_MASK));
   static_assert(static_cast<uint32_t>(UNWIND_X86_64_MODE_STACK_IND) ==
                 static_cast<uint32_t>(UNWIND_X86_MODE_STACK_IND));
   if ((target->cpuType == CPU_TYPE_X86_64 || target->cpuType == CPU_TYPE_X86) &&
-      (encoding & UNWIND_X86_64_MODE_MASK) == UNWIND_X86_64_MODE_STACK_IND) {
+      (encoding & UNWIND_MODE_MASK) == UNWIND_X86_64_MODE_STACK_IND) {
     // FIXME: Consider passing in the two function addresses and getting
     // their two stack sizes off the `subq` and only returning false if they're
     // actually 
diff erent.