[lldb] [Process/elf-core] Fix reading FPRs from FreeBSD/i386 cores

[mgorny]

Summary

The FreeBSD coredumps from i386 systems contain only FSAVE-style
NT_FPREGSET. Since we do not really support reading that kind of data
anymore, just use NT_X86_XSTATE to get FXSAVE-style data when available.

[mgorny]

Also add FPU-specific checks to x86-32-freebsd-addr.test.

[emaste]

LGTM

lldb/source/Plugins/Process/elf-core/RegisterUtilities.h

 //===-- RegisterUtilities.h -------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLDB_SOURCE_PLUGINS_PROCESS_ELF_CORE_REGISTERUTILITIES_H
 #define LLDB_SOURCE_PLUGINS_PROCESS_ELF_CORE_REGISTERUTILITIES_H
 
 #include "Plugins/ObjectFile/ELF/ObjectFileELF.h"
 #include "lldb/Utility/DataExtractor.h"
 #include "llvm/BinaryFormat/ELF.h"
 
 namespace lldb_private {
 /// Core files PT_NOTE segment descriptor types
 
 namespace NETBSD {
 enum { NT_PROCINFO = 1, NT_AUXV = 2 };

 // to override a more general entry (e.g. general linux), as long as you place
 // it earlier in the list. If a register set is not found, it returns an empty
 // DataExtractor.
 DataExtractor getRegset(llvm::ArrayRef<CoreNote> Notes,
                         const llvm::Triple &Triple,
                         llvm::ArrayRef<RegsetDesc> RegsetDescs);
 
 constexpr RegsetDesc FPR_Desc[] = {
+    // FreeBSD/i386 core NT_FPREGSET is x87 FSAVE result but the XSAVE dump
+    // starts with FXSAVE struct, so use that instead if available.
+    {llvm::Triple::FreeBSD, llvm::Triple::x86, llvm::ELF::NT_X86_XSTATE},
     {llvm::Triple::FreeBSD, llvm::Triple::UnknownArch, llvm::ELF::NT_FPREGSET},
     // In a i386 core file NT_FPREGSET is present, but it's not the result
     // of the FXSAVE instruction like in 64 bit files.
     // The result from FXSAVE is in NT_PRXFPREG for i386 core files
     {llvm::Triple::Linux, llvm::Triple::x86, llvm::ELF::NT_PRXFPREG},
     {llvm::Triple::Linux, llvm::Triple::UnknownArch, llvm::ELF::NT_FPREGSET},
     {llvm::Triple::NetBSD, llvm::Triple::aarch64, NETBSD::AARCH64::NT_FPREGS},
     {llvm::Triple::NetBSD, llvm::Triple::x86_64, NETBSD::AMD64::NT_FPREGS},

lldb/test/Shell/Register/Core/x86-32-freebsd-fp.test

+# RUN: %lldb -b -s %s -c %p/Inputs/x86-32-freebsd.core | FileCheck %p/Inputs/x86-fp.check
+
+register read --all