[PATCH v3 03/10] accel/tcg: Use one_insn_per_tb global instead of old singlestep global

[Peter Maydell <peter.maydell@linaro.org>]

The only place left that looks at the old 'singlestep' global
variable is the TCG curr_cflags() function.  Replace the old global
with a new 'one_insn_per_tb' which is defined in tcg-all.c and
declared in accel/tcg/internal.h.  This keeps it restricted to the
TCG code, unlike 'singlestep' which was available to every file in
the system and defined in multiple different places for softmmu vs
linux-user vs bsd-user.

While we're making this change, use qatomic_read() and qatomic_set()
on the accesses to the new global, because TCG will read it without
holding a lock.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
In discussion on v2, we talked about combining this with the
'nochain' flag so as to have a single 'tcg_cflags_global' that
held the flags for the current (one_insn_per_tb, nochain) state.
I have not attempted that here, because it's a little tricky:
 * util/log.c is built into some binaries that don't have an
   accelerator at all (the tools), so it can't simply call
   current_accel() to get the TCG accelerator
 * the initial value of the logging flags is set before the
   TCG accelerator is even created
So I leave that to somebody else to have a go at if they like.
---
 accel/tcg/internal.h      | 2 ++
 include/exec/cpu-common.h | 2 --
 accel/tcg/cpu-exec.c      | 2 +-
 accel/tcg/tcg-all.c       | 6 ++++--
 bsd-user/main.c           | 1 -
 linux-user/main.c         | 1 -
 softmmu/globals.c         | 1 -
 7 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/accel/tcg/internal.h b/accel/tcg/internal.h
index 96f198b28b4..7bb0fdbe149 100644
--- a/accel/tcg/internal.h
+++ b/accel/tcg/internal.h
@@ -67,4 +67,6 @@ static inline target_ulong log_pc(CPUState *cpu, const TranslationBlock *tb)
 extern int64_t max_delay;
 extern int64_t max_advance;
 
+extern bool one_insn_per_tb;
+
 #endif /* ACCEL_TCG_INTERNAL_H */
diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
index 6feaa40ca7b..0be74f1e706 100644
--- a/include/exec/cpu-common.h
+++ b/include/exec/cpu-common.h
@@ -163,8 +163,6 @@ int cpu_memory_rw_debug(CPUState *cpu, vaddr addr,
                         void *ptr, size_t len, bool is_write);
 
 /* vl.c */
-extern int singlestep;
-
 void list_cpus(const char *optarg);
 
 #endif /* CPU_COMMON_H */
diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
index 8370c92c05e..bc0e1c3299a 100644
--- a/accel/tcg/cpu-exec.c
+++ b/accel/tcg/cpu-exec.c
@@ -159,7 +159,7 @@ uint32_t curr_cflags(CPUState *cpu)
      */
     if (unlikely(cpu->singlestep_enabled)) {
         cflags |= CF_NO_GOTO_TB | CF_NO_GOTO_PTR | CF_SINGLE_STEP | 1;
-    } else if (singlestep) {
+    } else if (qatomic_read(&one_insn_per_tb)) {
         cflags |= CF_NO_GOTO_TB | 1;
     } else if (qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) {
         cflags |= CF_NO_GOTO_TB;
diff --git a/accel/tcg/tcg-all.c b/accel/tcg/tcg-all.c
index fcf361c8db6..a831f8d7c37 100644
--- a/accel/tcg/tcg-all.c
+++ b/accel/tcg/tcg-all.c
@@ -31,6 +31,7 @@
 #include "qapi/error.h"
 #include "qemu/error-report.h"
 #include "qemu/accel.h"
+#include "qemu/atomic.h"
 #include "qapi/qapi-builtin-visit.h"
 #include "qemu/units.h"
 #if !defined(CONFIG_USER_ONLY)
@@ -110,6 +111,7 @@ static void tcg_accel_instance_init(Object *obj)
 }
 
 bool mttcg_enabled;
+bool one_insn_per_tb;
 
 static int tcg_init_machine(MachineState *ms)
 {
@@ -219,8 +221,8 @@ static void tcg_set_one_insn_per_tb(Object *obj, bool value, Error **errp)
 {
     TCGState *s = TCG_STATE(obj);
     s->one_insn_per_tb = value;
-    /* For the moment, set the global also: this changes the behaviour */
-    singlestep = value;
+    /* Set the global also: this changes the behaviour */
+    qatomic_set(&one_insn_per_tb, value);
 }
 
 static int tcg_gdbstub_supported_sstep_flags(void)
diff --git a/bsd-user/main.c b/bsd-user/main.c
index 09b84da190c..a9e5a127d38 100644
--- a/bsd-user/main.c
+++ b/bsd-user/main.c
@@ -49,7 +49,6 @@
 #include "host-os.h"
 #include "target_arch_cpu.h"
 
-int singlestep;
 static bool opt_one_insn_per_tb;
 uintptr_t guest_base;
 bool have_guest_base;
diff --git a/linux-user/main.c b/linux-user/main.c
index 489694ad654..c7020b413bc 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -68,7 +68,6 @@
 char *exec_path;
 char real_exec_path[PATH_MAX];
 
-int singlestep;
 static bool opt_one_insn_per_tb;
 static const char *argv0;
 static const char *gdbstub;
diff --git a/softmmu/globals.c b/softmmu/globals.c
index 39678aa8c58..e83b5428d12 100644
--- a/softmmu/globals.c
+++ b/softmmu/globals.c
@@ -43,7 +43,6 @@ int vga_interface_type = VGA_NONE;
 bool vga_interface_created;
 Chardev *parallel_hds[MAX_PARALLEL_PORTS];
 int win2k_install_hack;
-int singlestep;
 int fd_bootchk = 1;
 int graphic_rotate;
 QEMUOptionRom option_rom[MAX_OPTION_ROMS];
-- 
2.34.1