Do not qualify the mcontext_t *mcp argument for set_mcontext(9) as

const.  On x86, even after the machine context is supposedly read into
the struct ucontext, lazy FPU state save code might only mark the FPU
data as hardware-owned.  Later, set_fpcontext() needs to fetch the
state from hardware, modifying the *mcp.

The set_mcontext(9) is called from sigreturn(2) and setcontext(2)
implementations and old create_thread(2) interface, which throw the
*mcp out after the set_mcontext() call.

Reported by:	dim
Discussed with:	jhb
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week

sys/amd64/amd64/machdep.c

@@ -157,7 +157,7 @@ extern u_int64_t hammer_time(u_int64_t, u_int64_t);
 static void cpu_startup(void *);
 static void get_fpcontext(struct thread *td, mcontext_t *mcp,
     char *xfpusave, size_t xfpusave_len);
-static int  set_fpcontext(struct thread *td, const mcontext_t *mcp,
+static int  set_fpcontext(struct thread *td, mcontext_t *mcp,
     char *xfpustate, size_t xfpustate_len);
 SYSINIT(cpu, SI_SUB_CPU, SI_ORDER_FIRST, cpu_startup, NULL);
 
@@ -2480,7 +2480,7 @@ get_mcontext(struct thread *td, mcontext_t *mcp, int flags)
  * touch the cs selector.
  */
 int
-set_mcontext(struct thread *td, const mcontext_t *mcp)
+set_mcontext(struct thread *td, mcontext_t *mcp)
 {
 	struct pcb *pcb;
 	struct trapframe *tp;
@@ -2567,7 +2567,7 @@ get_fpcontext(struct thread *td, mcontext_t *mcp, char *xfpusave,
 }
 
 static int
-set_fpcontext(struct thread *td, const mcontext_t *mcp, char *xfpustate,
+set_fpcontext(struct thread *td, mcontext_t *mcp, char *xfpustate,
     size_t xfpustate_len)
 {
 	struct savefpu *fpstate;

sys/amd64/ia32/ia32_signal.c

@@ -118,7 +118,7 @@ ia32_get_fpcontext(struct thread *td, struct ia32_mcontext *mcp,
 }
 
 static int
-ia32_set_fpcontext(struct thread *td, const struct ia32_mcontext *mcp,
+ia32_set_fpcontext(struct thread *td, struct ia32_mcontext *mcp,
     char *xfpustate, size_t xfpustate_len)
 {
 	int error;
@@ -197,7 +197,7 @@ ia32_get_mcontext(struct thread *td, struct ia32_mcontext *mcp, int flags)
  * touch the cs selector.
  */
 static int
-ia32_set_mcontext(struct thread *td, const struct ia32_mcontext *mcp)
+ia32_set_mcontext(struct thread *td, struct ia32_mcontext *mcp)
 {
 	struct trapframe *tp;
 	char *xfpustate;

sys/arm/arm/machdep.c

@@ -700,7 +700,7 @@ get_mcontext(struct thread *td, mcontext_t *mcp, int clear_ret)
  * touch the cs selector.
  */
 int
-set_mcontext(struct thread *td, const mcontext_t *mcp)
+set_mcontext(struct thread *td, mcontext_t *mcp)
 {
 	struct trapframe *tf = td->td_frame;
 	const __greg_t *gr = mcp->__gregs;

sys/i386/i386/machdep.c

@@ -195,7 +195,7 @@ static void cpu_startup(void *);
 static void fpstate_drop(struct thread *td);
 static void get_fpcontext(struct thread *td, mcontext_t *mcp,
     char *xfpusave, size_t xfpusave_len);
-static int  set_fpcontext(struct thread *td, const mcontext_t *mcp,
+static int  set_fpcontext(struct thread *td, mcontext_t *mcp,
     char *xfpustate, size_t xfpustate_len);
 #ifdef CPU_ENABLE_SSE
 static void set_fpregs_xmm(struct save87 *, struct savexmm *);
@@ -3856,7 +3856,7 @@ get_mcontext(struct thread *td, mcontext_t *mcp, int flags)
  * touch the cs selector.
  */
 int
-set_mcontext(struct thread *td, const mcontext_t *mcp)
+set_mcontext(struct thread *td, mcontext_t *mcp)
 {
 	struct trapframe *tp;
 	char *xfpustate;
@@ -3934,7 +3934,7 @@ get_fpcontext(struct thread *td, mcontext_t *mcp, char *xfpusave,
 }
 
 static int
-set_fpcontext(struct thread *td, const mcontext_t *mcp, char *xfpustate,
+set_fpcontext(struct thread *td, mcontext_t *mcp, char *xfpustate,
     size_t xfpustate_len)
 {
 	union savefpu *fpstate;

sys/mips/mips/freebsd32_machdep.c

@@ -68,7 +68,7 @@
 
 static void freebsd32_exec_setregs(struct thread *, struct image_params *, u_long);
 static int get_mcontext32(struct thread *, mcontext32_t *, int);
-static int set_mcontext32(struct thread *, const mcontext32_t *);
+static int set_mcontext32(struct thread *, mcontext32_t *);
 static void freebsd32_sendsig(sig_t, ksiginfo_t *, sigset_t *);
 
 extern const char *freebsd32_syscallnames[];
@@ -227,7 +227,7 @@ get_mcontext32(struct thread *td, mcontext32_t *mcp, int flags)
 }
 
 static int
-set_mcontext32(struct thread *td, const mcontext32_t *mcp)
+set_mcontext32(struct thread *td, mcontext32_t *mcp)
 {
 	mcontext_t mcp64;
 	unsigned i;

sys/mips/mips/pm_machdep.c

@@ -375,7 +375,7 @@ get_mcontext(struct thread *td, mcontext_t *mcp, int flags)
 }
 
 int
-set_mcontext(struct thread *td, const mcontext_t *mcp)
+set_mcontext(struct thread *td, mcontext_t *mcp)
 {
 	struct trapframe *tp;
 

sys/powerpc/powerpc/exec_machdep.c

@@ -442,7 +442,7 @@ get_mcontext(struct thread *td, mcontext_t *mcp, int flags)
 }
 
 int
-set_mcontext(struct thread *td, const mcontext_t *mcp)
+set_mcontext(struct thread *td, mcontext_t *mcp)
 {
 	struct pcb *pcb;
 	struct trapframe *tf;
@@ -739,7 +739,7 @@ get_mcontext32(struct thread *td, mcontext32_t *mcp, int flags)
 }
 
 static int
-set_mcontext32(struct thread *td, const mcontext32_t *mcp)
+set_mcontext32(struct thread *td, mcontext32_t *mcp)
 {
 	mcontext_t mcp64;
 	int i, error;

sys/sparc64/sparc64/machdep.c

@@ -811,7 +811,7 @@ get_mcontext(struct thread *td, mcontext_t *mc, int flags)
 }
 
 int
-set_mcontext(struct thread *td, const mcontext_t *mc)
+set_mcontext(struct thread *td, mcontext_t *mc)
 {
 	struct trapframe *tf;
 	struct pcb *pcb;

sys/sys/ucontext.h

@@ -99,7 +99,7 @@ struct thread;
 
 /* Machine-dependent functions: */
 int	get_mcontext(struct thread *, mcontext_t *, int);
-int	set_mcontext(struct thread *, const mcontext_t *);
+int	set_mcontext(struct thread *, mcontext_t *);
 
 #endif /* !_KERNEL */