Fix core files for 32 bit architectures that are supported in ProcessELFCore.cpp

[clayborg]

Summary

Core files need to know the size of the PRSTATUS header so that we can grab the register values that follow it. The code that figure out this size was using a hard coded list of architecture cores instead of relying on 32 or 64 bit for most cores.

The fix here fixes core files for 32 bit ARM. Prior to this the PRSTATUS header size was being returned as zero and the register values were being taken from the first bytes of the PRSTATUS struct (signo, etc).

[zturner]

source/Plugins/Process/elf-core/ThreadElfCore.cpp

277

subtracting 40 from the header size seems a bit magical to those not in the know (such as myself). Could you do something like:

if (arch.GetAddressByteSize() == 8)
    return sizeof(ELFLinuxPrStatus);

lldbassert(arch.GetAddressByteSize() == 4);
constexpr int kWhatever = 10;
return sizeof(ELFLinuxPrStatus) - kWhatever * arch.GetAddressByteSize();

[clayborg]

Fix zturner's suggestion.

packages/Python/lldbsuite/test/functionalities/postmortem/elf-core/TestLinuxCore.py

def test_i386_sysroot(self):
         self.assertTrue(target, VALID_TARGET)
         process = target.LoadCore("linux-i386.core")
 
         # Check that we found a.out from the sysroot
         self.check_all(process, self._i386_pid, self._i386_regions, "a.out")
 
         self.dbg.DeleteTarget(target)
 
+    @skipIf(triple='^mips')
+    @skipIfLLVMTargetMissing("ARM")
+    def test_arm_core(self):
+        # check 32 bit ARM core file
+        target = self.dbg.CreateTarget(None)
+        self.assertTrue(target, VALID_TARGET)
+        process = target.LoadCore("linux-arm.core")
+
+        values = {}
+        values["r0"] = "0x00000000"
+        values["r1"] = "0x00000001"
+        values["r2"] = "0x00000002"
+        values["r3"] = "0x00000003"
+        values["r4"] = "0x00000004"
+        values["r5"] = "0x00000005"
+        values["r6"] = "0x00000006"
+        values["r7"] = "0x00000007"
+        values["r8"] = "0x00000008"
+        values["r9"] = "0x00000009"
+        values["r10"] = "0x0000000a"
+        values["r11"] = "0x0000000b"
+        values["r12"] = "0x0000000c"
+        values["sp"] = "0x0000000d"
+        values["lr"] = "0x0000000e"
+        values["pc"] = "0x0000000f"
+        values["cpsr"] = "0x00000010"
+        for regname, value in values.items():
+            self.expect("register read {}".format(regname), substrs=["{} = {}".format(regname, value)])
+
     def check_memory_regions(self, process, region_count):
         region_list = process.GetMemoryRegions()
         self.assertEqual(region_list.GetSize(), region_count)
 
         region = lldb.SBMemoryRegionInfo()
 
         # Check we have the right number of regions.
         self.assertEqual(region_list.GetSize(), region_count)

source/Plugins/Process/elf-core/ThreadElfCore.cpp

 //----------------------------------------------------------------
 ELFLinuxPrStatus::ELFLinuxPrStatus() {
   memset(this, 0, sizeof(ELFLinuxPrStatus));
 }
 
 size_t ELFLinuxPrStatus::GetSize(const lldb_private::ArchSpec &arch) {
   constexpr size_t mips_linux_pr_status_size_o32 = 96;
   constexpr size_t mips_linux_pr_status_size_n32 = 72;
+  constexpr size_t num_ptr_size_members = 10;
   if (arch.IsMIPS()) {
     std::string abi = arch.GetTargetABI();
     assert(!abi.empty() && "ABI is not set");
     if (!abi.compare("n64"))
       return sizeof(ELFLinuxPrStatus);
     else if (!abi.compare("o32"))
       return mips_linux_pr_status_size_o32;
     // N32 ABI
     return mips_linux_pr_status_size_n32;
   }
   switch (arch.GetCore()) {
-  case lldb_private::ArchSpec::eCore_s390x_generic:
-  case lldb_private::ArchSpec::eCore_x86_64_x86_64:
-  case lldb_private::ArchSpec::eCore_ppc64le_generic:
-    return sizeof(ELFLinuxPrStatus);
   case lldb_private::ArchSpec::eCore_x86_32_i386:
   case lldb_private::ArchSpec::eCore_x86_32_i486:
     return 72;
   default:
-    return 0;
+    if (arch.GetAddressByteSize() == 8)
+      return sizeof(ELFLinuxPrStatus);
+    else
+      return sizeof(ELFLinuxPrStatus) - num_ptr_size_members * 4;
   }
 }
 
 Status ELFLinuxPrStatus::Parse(const DataExtractor &data,
                                const ArchSpec &arch) {
   Status error;
   if (GetSize(arch) > data.GetByteSize()) {
     error.SetErrorStringWithFormat(