[RFC PATCH 2/3] target/i386/cpu: Allow to limit the 64-bit binary to 32-bit mode only

[Thomas Huth <thuth@redhat.com>]

qemu-system-x86_64 is pretty much a proper superset of qemu-system-i386,
so in the long run, it does not make too much sense that we continuously
build two binaries here.
However, some people still might want to start QEMU in a mode that limits
the environment to 32-bit. Thus allow qemu-system-x86_64 to run in 32-bit
mode if the binary name ends in "-i386".

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 target/i386/cpu.h     |  4 ++--
 target/i386/cpu.c     | 28 +++++++++++++---------------
 target/i386/gdbstub.c |  8 +-------
 3 files changed, 16 insertions(+), 24 deletions(-)

diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index d243e290d3..5cb2eb3493 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -40,8 +40,8 @@
 #define TARGET_HAS_PRECISE_SMC
 
 #ifdef TARGET_X86_64
-#define I386_ELF_MACHINE  EM_X86_64
-#define ELF_MACHINE_UNAME "x86_64"
+#define I386_ELF_MACHINE  (qemu_target_only_32bits() ? EM_386 : EM_X86_64)
+#define ELF_MACHINE_UNAME (qemu_target_only_32bits() ? "i686" : "x86_64")
 #else
 #define I386_ELF_MACHINE  EM_386
 #define ELF_MACHINE_UNAME "i686"
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 2e30e348a1..f713005476 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -5093,11 +5093,9 @@ uint64_t x86_cpu_get_supported_feature_word(FeatureWord w,
     } else {
         return ~0;
     }
-#ifndef TARGET_X86_64
-    if (w == FEAT_8000_0001_EDX) {
+    if (qemu_target_only_32bits() && w == FEAT_8000_0001_EDX) {
         r &= ~CPUID_EXT2_LM;
     }
-#endif
     if (migratable_only) {
         r &= x86_cpu_get_migratable_flags(w);
     }
@@ -5267,11 +5265,11 @@ static void x86_cpu_load_model(X86CPU *cpu, X86CPUModel *model)
 
 static gchar *x86_gdb_arch_name(CPUState *cs)
 {
-#ifdef TARGET_X86_64
-    return g_strdup("i386:x86-64");
-#else
-    return g_strdup("i386");
-#endif
+    if (qemu_target_only_32bits()) {
+        return g_strdup("i386");
+    } else {
+        return g_strdup("i386:x86-64");
+    }
 }
 
 static void x86_cpu_cpudef_class_init(ObjectClass *oc, void *data)
@@ -7295,13 +7293,13 @@ static void x86_cpu_common_class_init(ObjectClass *oc, void *data)
 #endif /* !CONFIG_USER_ONLY */
 
     cc->gdb_arch_name = x86_gdb_arch_name;
-#ifdef TARGET_X86_64
-    cc->gdb_core_xml_file = "i386-64bit.xml";
-    cc->gdb_num_core_regs = 66;
-#else
-    cc->gdb_core_xml_file = "i386-32bit.xml";
-    cc->gdb_num_core_regs = 50;
-#endif
+    if (qemu_target_only_32bits()) {
+        cc->gdb_core_xml_file = "i386-32bit.xml";
+        cc->gdb_num_core_regs = 50;
+    } else {
+        cc->gdb_core_xml_file = "i386-64bit.xml";
+        cc->gdb_num_core_regs = 66;
+    }
     cc->disas_set_info = x86_disas_set_info;
 
     dc->user_creatable = true;
diff --git a/target/i386/gdbstub.c b/target/i386/gdbstub.c
index ebb000df6a..35a56b317c 100644
--- a/target/i386/gdbstub.c
+++ b/target/i386/gdbstub.c
@@ -72,15 +72,9 @@ static const int gpr_map32[8] = { 0, 1, 2, 3, 4, 5, 6, 7 };
 #define IDX_CTL_CR8_REG     (IDX_CTL_REGS + 4)
 #define IDX_CTL_EFER_REG    (IDX_CTL_REGS + 5)
 
-#ifdef TARGET_X86_64
-#define GDB_FORCE_64 1
-#else
-#define GDB_FORCE_64 0
-#endif
-
 static int gdb_read_reg_cs64(uint32_t hflags, GByteArray *buf, target_ulong val)
 {
-    if ((hflags & HF_CS64_MASK) || GDB_FORCE_64) {
+    if ((hflags & HF_CS64_MASK) || !qemu_target_only_32bits()) {
         return gdb_get_reg64(buf, val);
     }
     return gdb_get_reg32(buf, val);
-- 
2.31.1