[PATCH 1/3] target/i386: split the FNINIT out of do_fsave()

[Matt Turner <mattst88@gmail.com>]

do_fsave() ends with an FNINIT, which is what the FSAVE instruction and
the signal frame setup both want, but it makes the helper unusable for a
caller that only wants to read the state out: recording the registers
would destroy them.

Move the FNINIT into helper_fsave() and cpu_x86_fsave(), and expose the
store alone as cpu_x86_fsave_noinit(). No functional change; the next
patch uses the new entry point to write the x87 registers to a guest
core dump.

Signed-off-by: Matt Turner <mattst88@gmail.com>
---
 target/i386/cpu.h            |  2 ++
 target/i386/tcg/fpu_helper.c | 13 +++++++++++--
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git ./target/i386/cpu.h ./target/i386/cpu.h
index 9ce8ca0038..2a543ee808 100644
--- ./target/i386/cpu.h
+++ ./target/i386/cpu.h
@@ -2717,6 +2717,8 @@ int cpu_x86_get_descr_debug(CPUX86State *env, unsigned int selector,
  */
 void cpu_x86_load_seg(CPUX86State *s, X86Seg seg_reg, int selector);
 void cpu_x86_fsave(CPUX86State *s, void *host, size_t len);
+/* As cpu_x86_fsave(), but leaving the FPU state undisturbed. */
+void cpu_x86_fsave_noinit(CPUX86State *s, void *host, size_t len);
 void cpu_x86_frstor(CPUX86State *s, void *host, size_t len);
 void cpu_x86_fxsave(CPUX86State *s, void *host, size_t len);
 void cpu_x86_fxrstor(CPUX86State *s, void *host, size_t len);
diff --git ./target/i386/tcg/fpu_helper.c ./target/i386/tcg/fpu_helper.c
index b812125efa..f7cf4220ff 100644
--- ./target/i386/tcg/fpu_helper.c
+++ ./target/i386/tcg/fpu_helper.c
@@ -2536,6 +2536,10 @@ void helper_fldenv(CPUX86State *env, target_ulong ptr, int data32)
     do_fldenv(&ac, ptr, data32);
 }
 
+/*
+ * Store the environment and the register stack, as FSAVE does, but
+ * without the FNINIT that FSAVE performs afterward.
+ */
 static void do_fsave(X86Access *ac, target_ulong ptr, int data32)
 {
     CPUX86State *env = ac->env;
@@ -2548,8 +2552,6 @@ static void do_fsave(X86Access *ac, target_ulong ptr, int data32)
         do_fstt(ac, ptr, tmp);
         ptr += 10;
     }
-
-    do_fninit(env);
 }
 
 void helper_fsave(CPUX86State *env, target_ulong ptr, int data32)
@@ -2559,6 +2561,7 @@ void helper_fsave(CPUX86State *env, target_ulong ptr, int data32)
 
     access_prepare(&ac, env, ptr, size, MMU_DATA_STORE, GETPC());
     do_fsave(&ac, ptr, data32);
+    do_fninit(env);
 }
 
 static void do_frstor(X86Access *ac, target_ulong ptr, int data32)
@@ -3085,6 +3088,12 @@ void helper_xrstor(CPUX86State *env, target_ulong ptr, uint64_t rfbm)
 
 #if defined(CONFIG_USER_ONLY)
 void cpu_x86_fsave(CPUX86State *env, void *host, size_t len)
+{
+    cpu_x86_fsave_noinit(env, host, len);
+    do_fninit(env);
+}
+
+void cpu_x86_fsave_noinit(CPUX86State *env, void *host, size_t len)
 {
     X86Access ac = {
         .haddr1 = host,
-- 
2.54.0