[Qemu-devel] [PATCH] Avoid allocating TCG resources in non-TCG mode

[Jan Kiszka <jan.kiszka@siemens.com>]

Do not allocate TCG-only resources like the translation buffer when
running over KVM or XEN. Saves a "few" bytes in the qemu address space
and is also conceptually cleaner.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

Note: Only tested on x86.

 bsd-user/main.c       |    3 ++-
 darwin-user/main.c    |    4 ++--
 exec.c                |   19 ++++++++++++++-----
 linux-user/main.c     |    3 ++-
 qemu-common.h         |    5 ++++-
 target-i386/helper.c  |    4 ++--
 target-ppc/helper.c   |    4 +++-
 target-s390x/helper.c |    2 +-
 vl.c                  |   14 +++++++-------
 9 files changed, 37 insertions(+), 21 deletions(-)

diff --git a/bsd-user/main.c b/bsd-user/main.c
index a63b877..cc7d4a3 100644
--- a/bsd-user/main.c
+++ b/bsd-user/main.c
@@ -905,7 +905,8 @@ int main(int argc, char **argv)
         cpu_model = "any";
 #endif
     }
-    cpu_exec_init_all(0);
+    tcg_exec_init(0);
+    cpu_exec_init_all();
     /* NOTE: we need to init the CPU at this stage to get
        qemu_host_page_size */
     env = cpu_init(cpu_model);
diff --git a/darwin-user/main.c b/darwin-user/main.c
index 72307ad..1a881a0 100644
--- a/darwin-user/main.c
+++ b/darwin-user/main.c
@@ -852,8 +852,8 @@ int main(int argc, char **argv)
 #error unsupported CPU
 #endif
     }
-    
-    cpu_exec_init_all(0);
+    tcg_exec_init(0);
+    cpu_exec_init_all();
     /* NOTE: we need to init the CPU at this stage to get
        qemu_host_page_size */
     env = cpu_init(cpu_model);
diff --git a/exec.c b/exec.c
index 476b507..2658cb2 100644
--- a/exec.c
+++ b/exec.c
@@ -570,16 +570,12 @@ static void code_gen_alloc(unsigned long tb_size)
 /* Must be called before using the QEMU cpus. 'tb_size' is the size
    (in bytes) allocated to the translation buffer. Zero means default
    size. */
-void cpu_exec_init_all(unsigned long tb_size)
+void tcg_exec_init(unsigned long tb_size)
 {
     cpu_gen_init();
     code_gen_alloc(tb_size);
     code_gen_ptr = code_gen_buffer;
     page_init();
-#if !defined(CONFIG_USER_ONLY)
-    memory_map_init();
-    io_mem_init();
-#endif
 #if !defined(CONFIG_USER_ONLY) || !defined(CONFIG_USE_GUEST_BASE)
     /* There's no guest base to take into account, so go ahead and
        initialize the prologue now.  */
@@ -587,6 +583,19 @@ void cpu_exec_init_all(unsigned long tb_size)
 #endif
 }
 
+bool tcg_enabled(void)
+{
+    return code_gen_buffer != NULL;
+}
+
+void cpu_exec_init_all(void)
+{
+#if !defined(CONFIG_USER_ONLY)
+    memory_map_init();
+    io_mem_init();
+#endif
+}
+
 #if defined(CPU_SAVE_VERSION) && !defined(CONFIG_USER_ONLY)
 
 static int cpu_common_post_load(void *opaque, int version_id)
diff --git a/linux-user/main.c b/linux-user/main.c
index 6a8f4bd..8e15474 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -3117,7 +3117,8 @@ int main(int argc, char **argv, char **envp)
         cpu_model = "any";
 #endif
     }
-    cpu_exec_init_all(0);
+    tcg_exec_init(0);
+    cpu_exec_init_all();
     /* NOTE: we need to init the CPU at this stage to get
        qemu_host_page_size */
     env = cpu_init(cpu_model);
diff --git a/qemu-common.h b/qemu-common.h
index 1e3c665..3440986 100644
--- a/qemu-common.h
+++ b/qemu-common.h
@@ -273,7 +273,10 @@ typedef struct VirtIODevice VirtIODevice;
 
 typedef uint64_t pcibus_t;
 
-void cpu_exec_init_all(unsigned long tb_size);
+void tcg_exec_init(unsigned long tb_size);
+bool tcg_enabled(void);
+
+void cpu_exec_init_all(void);
 
 /* CPU save/load.  */
 void cpu_save(QEMUFile *f, void *opaque);
diff --git a/target-i386/helper.c b/target-i386/helper.c
index 182009a..3332195 100644
--- a/target-i386/helper.c
+++ b/target-i386/helper.c
@@ -1243,8 +1243,8 @@ CPUX86State *cpu_x86_init(const char *cpu_model)
     cpu_exec_init(env);
     env->cpu_model_str = cpu_model;
 
-    /* init various static tables */
-    if (!inited) {
+    /* init various static tables used in TCG mode */
+    if (tcg_enabled() && !inited) {
         inited = 1;
         optimize_flags_init();
 #ifndef CONFIG_USER_ONLY
diff --git a/target-ppc/helper.c b/target-ppc/helper.c
index 176128a..e00b3e6 100644
--- a/target-ppc/helper.c
+++ b/target-ppc/helper.c
@@ -3091,7 +3091,9 @@ CPUPPCState *cpu_ppc_init (const char *cpu_model)
 
     env = qemu_mallocz(sizeof(CPUPPCState));
     cpu_exec_init(env);
-    ppc_translate_init();
+    if (tcg_enabled()) {
+        ppc_translate_init();
+    }
     env->cpu_model_str = cpu_model;
     cpu_ppc_register_internal(env, def);
 
diff --git a/target-s390x/helper.c b/target-s390x/helper.c
index 1ce7079..443bb1d 100644
--- a/target-s390x/helper.c
+++ b/target-s390x/helper.c
@@ -81,7 +81,7 @@ CPUS390XState *cpu_s390x_init(const char *cpu_model)
 
     env = qemu_mallocz(sizeof(CPUS390XState));
     cpu_exec_init(env);
-    if (!inited) {
+    if (tcg_enabled() && !inited) {
         inited = 1;
         s390x_translate_init();
     }
diff --git a/vl.c b/vl.c
index 26bee4e..cc4998f 100644
--- a/vl.c
+++ b/vl.c
@@ -265,6 +265,7 @@ int kvm_allowed = 0;
 int xen_allowed = 0;
 uint32_t xen_domid;
 enum xen_mode xen_mode = XEN_EMULATE;
+static int tcg_tb_size;
 
 static int default_serial = 1;
 static int default_parallel = 1;
@@ -1942,6 +1943,7 @@ static QEMUMachine *machine_parse(const char *name)
 
 static int tcg_init(void)
 {
+    tcg_exec_init(tcg_tb_size * 1024 * 1024);
     return 0;
 }
 
@@ -2102,7 +2104,6 @@ int main(int argc, char **argv, char **envp)
     const char *loadvm = NULL;
     QEMUMachine *machine;
     const char *cpu_model;
-    int tb_size;
     const char *pid_file = NULL;
     const char *incoming = NULL;
 #ifdef CONFIG_VNC
@@ -2142,7 +2143,6 @@ int main(int argc, char **argv, char **envp)
     nb_numa_nodes = 0;
     nb_nics = 0;
 
-    tb_size = 0;
     autostart= 1;
 
     /* first pass of option parsing */
@@ -2857,9 +2857,10 @@ int main(int argc, char **argv, char **envp)
                 configure_rtc(opts);
                 break;
             case QEMU_OPTION_tb_size:
-                tb_size = strtol(optarg, NULL, 0);
-                if (tb_size < 0)
-                    tb_size = 0;
+                tcg_tb_size = strtol(optarg, NULL, 0);
+                if (tcg_tb_size < 0) {
+                    tcg_tb_size = 0;
+                }
                 break;
             case QEMU_OPTION_icount:
                 icount_option = optarg;
@@ -3133,8 +3134,7 @@ int main(int argc, char **argv, char **envp)
         }
     }
 
-    /* init the dynamic translator */
-    cpu_exec_init_all(tb_size * 1024 * 1024);
+    cpu_exec_init_all();
 
     bdrv_init_with_whitelist();
 
-- 
1.7.3.4