[AArch64] [Windows] Fix llvm-readobj -unwind output with many epilogs.

[efriedma]

Summary

The number of epilog scopes may not fit into a uint8_t.

Fixes https://bugs.llvm.org/show_bug.cgi?id=40855

[rnk]

lgtm

llvm/trunk/include/llvm/Support/ARMWinEH.h

bool E() const {
     return ((Data[0] & 0x00200000) >> 21);
   }
 
   bool F() const {
     assert(!isAArch64 && "Fragments are only supported on ARMv7 WinEH");
     return ((Data[0] & 0x00400000) >> 22);
   }
 
-  uint8_t EpilogueCount() const {
+  uint16_t EpilogueCount() const {
     if (HeaderWords(*this) == 1) {
       if (isAArch64)
         return (Data[0] & 0x07C00000) >> 22;
       return (Data[0] & 0x0f800000) >> 23;
     }
     return Data[1] & 0x0000ffff;
   }
 

llvm/trunk/test/tools/llvm-readobj/arm64-many-epilogs.s

+// REQUIRES: aarch64-registered-target
+// RUN: llvm-mc -filetype=obj -triple aarch64-windows %s -o - \
+// RUN:   | not llvm-readobj -unwind - | FileCheck %s
+
+// Older versions of LLVM had a bug where we would accidentally
+// truncate the number of epilogue scopes to a uint8_t; make
+// sure this doesn't happen.
+//
+// We expect the llvm-readobj invocation to fail because the
+// xdata section is truncated (to reduce the size of the testcase).
+
+// CHECK: EpilogueScopes: 256
+
+.section .pdata,"dr"
+        .long "?func@@YAHXZ"@IMGREL
+        .long "$unwind$func@@YAHXZ"@IMGREL
+
+        .text
+        .globl  "?func@@YAHXZ"
+        .p2align        3
+"?func@@YAHXZ":
+        ret
+
+.section        .xdata,"dr"
+"$unwind$func@@YAHXZ":
+.long 0x00000000, 0x02010100, 0x09000000, 0x0A000000