i386/gdbstub: Add APX support for gdbstub

Add i386-64bit-apx.xml from gdb to allow QEMU gdbstub parse APX EGPRs,
and implement the callbacks to allow gdbstub access EGPRs of guest.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Tested-by: Xudong Hao <xudong.hao@intel.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20251211070942.3612547-5-zhao1.liu@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configs/targets/x86_64-softmmu.mak

@@ -2,5 +2,5 @@ TARGET_ARCH=x86_64
 TARGET_BASE_ARCH=i386
 TARGET_KVM_HAVE_GUEST_DEBUG=y
 TARGET_KVM_HAVE_RESET_PARKED_VCPU=y
-TARGET_XML_FILES= gdb-xml/i386-64bit.xml
+TARGET_XML_FILES= gdb-xml/i386-64bit.xml gdb-xml/i386-64bit-apx.xml
 TARGET_LONG_BITS=64

gdb-xml/i386-64bit-apx.xml

@@ -0,0 +1,26 @@
+<?xml version="1.0"?>
+<!-- Copyright (C) 2024 Free Software Foundation, Inc.
+
+     Copying and distribution of this file, with or without modification,
+     are permitted in any medium without royalty provided the copyright
+     notice and this notice are preserved.  -->
+
+<!DOCTYPE feature SYSTEM "gdb-target.dtd">
+<feature name="org.gnu.gdb.i386.apx">
+  <reg name="r16" bitsize="64" type="int64"/>
+  <reg name="r17" bitsize="64" type="int64"/>
+  <reg name="r18" bitsize="64" type="int64"/>
+  <reg name="r19" bitsize="64" type="int64"/>
+  <reg name="r20" bitsize="64" type="int64"/>
+  <reg name="r21" bitsize="64" type="int64"/>
+  <reg name="r22" bitsize="64" type="int64"/>
+  <reg name="r23" bitsize="64" type="int64"/>
+  <reg name="r24" bitsize="64" type="int64"/>
+  <reg name="r25" bitsize="64" type="int64"/>
+  <reg name="r26" bitsize="64" type="int64"/>
+  <reg name="r27" bitsize="64" type="int64"/>
+  <reg name="r28" bitsize="64" type="int64"/>
+  <reg name="r29" bitsize="64" type="int64"/>
+  <reg name="r30" bitsize="64" type="int64"/>
+  <reg name="r31" bitsize="64" type="int64"/>
+</feature>

target/i386/cpu.h

@@ -61,6 +61,22 @@ enum {
     R_R13 = 13,
     R_R14 = 14,
     R_R15 = 15,
+    R_R16 = 16,
+    R_R17 = 17,
+    R_R18 = 18,
+    R_R19 = 19,
+    R_R20 = 20,
+    R_R21 = 21,
+    R_R22 = 22,
+    R_R23 = 23,
+    R_R24 = 24,
+    R_R25 = 25,
+    R_R26 = 26,
+    R_R27 = 27,
+    R_R28 = 28,
+    R_R29 = 29,
+    R_R30 = 30,
+    R_R31 = 31,
 
     R_AL = 0,
     R_CL = 1,

target/i386/gdbstub.c

@@ -27,9 +27,11 @@
 #endif
 
 #ifdef TARGET_X86_64
-static const int gpr_map[16] = {
+static const int gpr_map[CPU_NB_EREGS] = {
     R_EAX, R_EBX, R_ECX, R_EDX, R_ESI, R_EDI, R_EBP, R_ESP,
-    8, 9, 10, 11, 12, 13, 14, 15
+    R_R8, R_R9, R_R10, R_R11, R_R12, R_R13, R_R14, R_R15,
+    R_R16, R_R17, R_R18, R_R19, R_R20, R_R21, R_R22, R_R23,
+    R_R24, R_R25, R_R26, R_R27, R_R28, R_R29, R_R30, R_R31,
 };
 #else
 #define gpr_map gpr_map32
@@ -444,8 +446,71 @@ static int x86_cpu_gdb_write_linux_register(CPUState *cs, uint8_t *mem_buf,
 
 #endif
 
+#ifdef TARGET_X86_64
+static int i386_cpu_gdb_get_egprs(CPUState *cs, GByteArray *mem_buf, int n)
+{
+    CPUX86State *env = &X86_CPU(cs)->env;
+
+    if (n >= 0 && n < EGPR_NUM) {
+        /* EGPRs can be only directly accessible in 64-bit mode. */
+        if (env->hflags & HF_CS64_MASK) {
+            return gdb_get_reg64(mem_buf, env->regs[gpr_map[n + CPU_NB_REGS]]);
+        } else {
+            return gdb_get_regl(mem_buf, 0);
+        }
+    }
+
+    return 0;
+}
+
+static int i386_cpu_gdb_set_egprs(CPUState *cs, uint8_t *mem_buf, int n)
+{
+    CPUX86State *env = &X86_CPU(cs)->env;
+
+    if (n >= 0 && n < EGPR_NUM) {
+        /*
+         * EGPRs can be only directly accessible in 64-bit mode, and require
+         * XCR0[APX_F] (at least for modification in gdbstub) to be enabled.
+         */
+        if (env->hflags & HF_CS64_MASK && env->xcr0 & XSTATE_APX_MASK) {
+            env->regs[gpr_map[n + CPU_NB_REGS]] = ldtul_p(mem_buf);
+
+            /*
+             * Per SDM Vol 1, "Processor Tracking of XSAVE-Managed State",
+             * XSTATE_BV[i] *may* be either 0 or 1 if the state component is
+             * in its initial configuration.
+             *
+             * However, it is observed on Diamond Rapids (DMR) that
+             * XSTATE_BV[APX_F] is set whenever EGPRs are modified, regardless
+             * of the value written (even if zero).
+             *
+             * Since GDB modifies the software register cache directly,
+             * manually force the bit set to emulate this behavior observed
+             * on hardware.
+             */
+            if (!(env->xstate_bv & XSTATE_APX_MASK)) {
+                env->xstate_bv |= XSTATE_APX_MASK;
+            }
+        }
+        return sizeof(target_ulong);
+    }
+    return 0;
+}
+#endif
+
 void x86_cpu_gdb_init(CPUState *cs)
 {
+#ifdef TARGET_X86_64
+    CPUX86State *env = &X86_CPU(cs)->env;
+
+    if (env->features[FEAT_7_1_EDX] & CPUID_7_1_EDX_APXF) {
+        gdb_register_coprocessor(cs, i386_cpu_gdb_get_egprs,
+                                 i386_cpu_gdb_set_egprs,
+                                 gdb_find_static_feature("i386-64bit-apx.xml"),
+                                 0);
+    }
+#endif
+
 #ifdef CONFIG_LINUX_USER
     gdb_register_coprocessor(cs, x86_cpu_gdb_read_linux_register,
                              x86_cpu_gdb_write_linux_register,