[RFC PATCH 1/3] cpu: Add a way to detect 32-bit mode from argv0

[Thomas Huth]

In the future, we might want to avoid compiling certain targets separately
for 32-bit mode (i.e. -i386, -arm and -ppc) where the 64-bit variant is a
superset of the 32-bit variant. But it would be good to provide a way to
mimic the 32-bit behavior via the program name in case the users need this
compatibility for some scenarios. Thus add a function that checks
for the old 32-bit program names and sets a flag accordingly.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 include/hw/core/cpu.h | 10 ++++++++++
 cpu.c                 | 13 +++++++++++++
 softmmu/vl.c          |  1 +
 3 files changed, 24 insertions(+)

diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
index 397fd3ac68..8fc15b7797 100644
--- a/include/hw/core/cpu.h
+++ b/include/hw/core/cpu.h
@@ -470,6 +470,15 @@ extern __thread CPUState *current_cpu;
 extern bool mttcg_enabled;
 #define qemu_tcg_mttcg_enabled() (mttcg_enabled)
 
+/**
+ * qemu_target_only_32bits:
+ * Check whether the target is 32 bits only (like i386 in contrast to x86_64).
+ *
+ * Returns: %true if we are running with a 32-bit only target
+ */
+extern bool target_only_32bits;
+#define qemu_target_only_32bits() (target_only_32bits)
+
 /**
  * cpu_paging_enabled:
  * @cpu: The CPU whose state is to be inspected.
@@ -1009,6 +1018,7 @@ void cpu_exec_unrealizefn(CPUState *cpu);
  */
 bool target_words_bigendian(void);
 
+void cpu_init_target_only_32bits(const char *argv0);
 void page_size_init(void);
 
 #ifdef NEED_CPU_H
diff --git a/cpu.c b/cpu.c
index 9105c85404..0b498f3a53 100644
--- a/cpu.c
+++ b/cpu.c
@@ -47,6 +47,8 @@
 uintptr_t qemu_host_page_size;
 intptr_t qemu_host_page_mask;
 
+bool target_only_32bits = (TARGET_LONG_BITS == 32);
+
 #ifndef CONFIG_USER_ONLY
 static int cpu_common_post_load(void *opaque, int version_id)
 {
@@ -427,6 +429,17 @@ bool target_words_bigendian(void)
 #endif
 }
 
+/*
+ * This is used for 64-bit targets that can also run in restricted 32-bit
+ * mode, e.g. if running as qemu-system-i386 instead of qemu-system-x86_64
+ */
+void cpu_init_target_only_32bits(const char *argv0)
+{
+    target_only_32bits |= g_str_has_suffix(argv0, "-i386") ||
+                          g_str_has_suffix(argv0, "-arm") ||
+                          g_str_has_suffix(argv0, "-ppc");
+}
+
 void page_size_init(void)
 {
     /* NOTE: we can always suppose that qemu_host_page_size >=
diff --git a/softmmu/vl.c b/softmmu/vl.c
index fb6c221e8e..51b35a6f0b 100644
--- a/softmmu/vl.c
+++ b/softmmu/vl.c
@@ -2677,6 +2677,7 @@ void qemu_init(int argc, char **argv)
 
     error_init(argv[0]);
     qemu_init_exec_dir(argv[0]);
+    cpu_init_target_only_32bits(argv[0]);
 
     qemu_init_arch_modules();
 
-- 
2.31.1