[lldb] [debugserver] Use "full" x86_64 GPR state when available.

macOS 10.15 added a "full" x86_64 GPR thread state flavor, equivalent to
the normal one but with DS, ES, SS, and GSbase added.
This flavor can only be used with processes that install a custom LDT
(functionality that was also added in 10.15 and is used by apps like
Wine to execute 32-bit code).

Along with allowing DS, ES, SS, and GSbase to be viewed/modified, using
the full flavor is necessary when debugging a thread executing 32-bit
code.
If thread_set_state() is used with the regular thread state flavor, the
kernel resets CS to the 64-bit code segment, which makes debugging
impossible.

There's no way to detect whether the full flavor is available, try to
use it and fall back to the regular one if it's not available.

A downside is that this patch exposes the DS, ES, SS, and GSbase
registers for all x86_64 processes, even though they are not populated
unless the full thread state is available.

Fixes #57591

Author: mrpippy

lldb/tools/debugserver/source/MacOSX/x86_64/DNBArchImplX86_64.cpp

@@ -182,22 +182,39 @@ kern_return_t DNBArchImplX86_64::GetGPRState(bool force) {
     m_state.context.gpr.__gs = ('g' << 8) + 's';
     m_state.SetError(e_regSetGPR, Read, 0);
 #else
-    mach_msg_type_number_t count = e_regSetWordSizeGPR;
+    mach_msg_type_number_t count = e_regSetWordSizeGPRFull;
+    int flavor = __x86_64_THREAD_FULL_STATE;
     m_state.SetError(
         e_regSetGPR, Read,
-        ::thread_get_state(m_thread->MachPortNumber(), __x86_64_THREAD_STATE,
+        ::thread_get_state(m_thread->MachPortNumber(), flavor,
                            (thread_state_t)&m_state.context.gpr, &count));
+
+    if (!m_state.GetError(e_regSetGPR, Read)) {
+      m_state.hasFullGPRState = true;
+    } else {
+      m_state.hasFullGPRState = false;
+      count = e_regSetWordSizeGPR;
+      flavor = __x86_64_THREAD_STATE;
+      m_state.SetError(
+          e_regSetGPR, Read,
+          ::thread_get_state(m_thread->MachPortNumber(), flavor,
+                             (thread_state_t)&m_state.context.gpr, &count));
+    }
     DNBLogThreadedIf(
         LOG_THREAD,
-        "::thread_get_state (0x%4.4x, %u, &gpr, %u) => 0x%8.8x"
+        "::thread_get_state (0x%4.4x, %u (%s), &gpr, %u) => 0x%8.8x"
         "\n\trax = %16.16llx rbx = %16.16llx rcx = %16.16llx rdx = %16.16llx"
         "\n\trdi = %16.16llx rsi = %16.16llx rbp = %16.16llx rsp = %16.16llx"
         "\n\t r8 = %16.16llx  r9 = %16.16llx r10 = %16.16llx r11 = %16.16llx"
         "\n\tr12 = %16.16llx r13 = %16.16llx r14 = %16.16llx r15 = %16.16llx"
         "\n\trip = %16.16llx"
-        "\n\tflg = %16.16llx  cs = %16.16llx  fs = %16.16llx  gs = %16.16llx",
-        m_thread->MachPortNumber(), x86_THREAD_STATE64,
-        x86_THREAD_STATE64_COUNT, m_state.GetError(e_regSetGPR, Read),
+        "\n\tflg = %16.16llx  cs = %16.16llx  fs = %16.16llx  gs = %16.16llx"
+        "\n\t ds = %16.16llx  es = %16.16llx  ss = %16.16llx gsB = %16.16llx",
+        m_thread->MachPortNumber(), flavor,
+        m_state.hasFullGPRState ? "full" : "non-full",
+        m_state.hasFullGPRState ? __x86_64_THREAD_FULL_STATE
+                                : __x86_64_THREAD_STATE,
+        m_state.GetError(e_regSetGPR, Read),
         m_state.context.gpr.__rax, m_state.context.gpr.__rbx,
         m_state.context.gpr.__rcx, m_state.context.gpr.__rdx,
         m_state.context.gpr.__rdi, m_state.context.gpr.__rsi,
@@ -208,7 +225,9 @@ kern_return_t DNBArchImplX86_64::GetGPRState(bool force) {
         m_state.context.gpr.__r14, m_state.context.gpr.__r15,
         m_state.context.gpr.__rip, m_state.context.gpr.__rflags,
         m_state.context.gpr.__cs, m_state.context.gpr.__fs,
-        m_state.context.gpr.__gs);
+        m_state.context.gpr.__gs, m_state.context.gpr.__ds,
+        m_state.context.gpr.__es, m_state.context.gpr.__ss,
+        m_state.context.gpr.__gsbase );
 
 //      DNBLogThreadedIf (LOG_THREAD, "thread_get_state(0x%4.4x, %u, &gpr, %u)
 //      => 0x%8.8x"
@@ -461,9 +480,11 @@ kern_return_t DNBArchImplX86_64::SetGPRState() {
 
   m_state.SetError(e_regSetGPR, Write,
                    ::thread_set_state(m_thread->MachPortNumber(),
-                                      __x86_64_THREAD_STATE,
+                                      m_state.hasFullGPRState ? __x86_64_THREAD_FULL_STATE
+                                                              : __x86_64_THREAD_STATE,
                                       (thread_state_t)&m_state.context.gpr,
-                                      e_regSetWordSizeGPR));
+                                      m_state.hasFullGPRState ? e_regSetWordSizeGPRFull
+                                                              : e_regSetWordSizeGPR));
   DNBLogThreadedIf(
       LOG_THREAD,
       "::thread_set_state (0x%4.4x, %u, &gpr, %u) => 0x%8.8x"
@@ -1157,6 +1178,10 @@ enum {
   gpr_cs,
   gpr_fs,
   gpr_gs,
+  gpr_ds,
+  gpr_es,
+  gpr_ss,
+  gpr_gsbase,
   gpr_eax,
   gpr_ebx,
   gpr_ecx,
@@ -1543,6 +1568,7 @@ enum debugserver_regnums {
   debugserver_k5 = 123,
   debugserver_k6 = 124,
   debugserver_k7 = 125,
+  debugserver_gsbase = 126,
 };
 
 #define GPR_OFFSET(reg) (offsetof(DNBArchImplX86_64::GPR, __##reg))
@@ -1690,6 +1716,10 @@ const DNBRegisterInfo DNBArchImplX86_64::g_gpr_registers[] = {
     DEFINE_GPR_ALT2(cs, NULL),
     DEFINE_GPR_ALT2(fs, NULL),
     DEFINE_GPR_ALT2(gs, NULL),
+    DEFINE_GPR_ALT2(ds, NULL),
+    DEFINE_GPR_ALT2(es, NULL),
+    DEFINE_GPR_ALT2(ss, NULL),
+    DEFINE_GPR_ALT2(gsbase, NULL),
     DEFINE_GPR_PSEUDO_32(eax, rax),
     DEFINE_GPR_PSEUDO_32(ebx, rbx),
     DEFINE_GPR_PSEUDO_32(ecx, rcx),
@@ -2313,6 +2343,8 @@ bool DNBArchImplX86_64::GetRegisterValue(uint32_t set, uint32_t reg,
     value->info = *regInfo;
     switch (set) {
     case e_regSetGPR:
+      if (reg > gpr_gs && !m_state.hasFullGPRState)
+        return false;
       if (reg < k_num_gpr_registers) {
         value->value.uint64 = ((uint64_t *)(&m_state.context.gpr))[reg];
         return true;
@@ -2524,6 +2556,8 @@ bool DNBArchImplX86_64::SetRegisterValue(uint32_t set, uint32_t reg,
   if (regInfo) {
     switch (set) {
     case e_regSetGPR:
+      if (reg > gpr_gs && !m_state.hasFullGPRState)
+        return false;
       if (reg < k_num_gpr_registers) {
         ((uint64_t *)(&m_state.context.gpr))[reg] = value->value.uint64;
         success = true;

lldb/tools/debugserver/source/MacOSX/x86_64/DNBArchImplX86_64.h

@@ -103,7 +103,8 @@ class DNBArchImplX86_64 : public DNBArchProtocol {
   };
 
   enum RegisterSetWordSize {
-    e_regSetWordSizeGPR = sizeof(GPR) / sizeof(int),
+    e_regSetWordSizeGPR = (sizeof(GPR) - 32) / sizeof(int),
+    e_regSetWordSizeGPRFull = sizeof(GPR) / sizeof(int),
     e_regSetWordSizeFPU = sizeof(FPU) / sizeof(int),
     e_regSetWordSizeEXC = sizeof(EXC) / sizeof(int),
     e_regSetWordSizeAVX = sizeof(AVX) / sizeof(int),
@@ -130,6 +131,7 @@ class DNBArchImplX86_64 : public DNBArchProtocol {
     kern_return_t fpu_errs[2]; // Read/Write errors
     kern_return_t exc_errs[2]; // Read/Write errors
     kern_return_t dbg_errs[2]; // Read/Write errors
+    bool hasFullGPRState;
 
     State() {
       uint32_t i;

lldb/tools/debugserver/source/MacOSX/x86_64/MachRegisterStatesX86_64.h

@@ -22,6 +22,7 @@
 #define __x86_64_DEBUG_STATE 11
 #define __x86_64_AVX_STATE 17
 #define __x86_64_AVX512F_STATE 20
+#define __x86_64_THREAD_FULL_STATE 23
 
 typedef struct {
   uint64_t __rax;
@@ -45,6 +46,10 @@ typedef struct {
   uint64_t __cs;
   uint64_t __fs;
   uint64_t __gs;
+  uint64_t __ds;
+  uint64_t __es;
+  uint64_t __ss;
+  uint64_t __gsbase;
 } __x86_64_thread_state_t;
 
 typedef struct {