Add API for obtaining extended machine context states that cannot be

fit into existing mcontext_t.

On i386 and amd64 do return the extended FPU states using
getcontextx(3). For other architectures, getcontextx(3) returns the
same information as getcontext(2).

Tested by:  pho
MFC after:  1 month

3 files changed, 36 insertions, 2 deletions

diff --git a/lib/libc/gen/Symbol.map b/lib/libc/gen/Symbol.map
index e00e746..d794c0a 100644
--- a/lib/libc/gen/Symbol.map
+++ b/lib/libc/gen/Symbol.map
@@ -384,6 +384,7 @@ FBSD_1.2 {
 FBSD_1.3 {
 	 fdlopen;
 	__FreeBSD_libc_enter_restricted_mode;
+	getcontextx;
 };
 
 FBSDprivate_1.0 {
@@ -507,4 +508,6 @@ FBSDprivate_1.0 {
 
 	__elf_aux_vector;
 	__pthread_map_stacks_exec;
+	__fillcontextx;
+	__getcontextx_size;
 };
diff --git a/lib/libc/gen/getcontext.3 b/lib/libc/gen/getcontext.3
index 2fda6b8..5b801fd 100644
--- a/lib/libc/gen/getcontext.3
+++ b/lib/libc/gen/getcontext.3
@@ -35,11 +35,11 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd September 10, 2002
+.Dd December 26, 2011
 .Dt GETCONTEXT 3
 .Os
 .Sh NAME
-.Nm getcontext , setcontext
+.Nm getcontext , getcontextx , setcontext
 .Nd get and set user thread context
 .Sh LIBRARY
 .Lb libc
@@ -59,6 +59,20 @@ This saved context may then later be restored by calling
 .Fn setcontext .
 .Pp
 The
+.Fn getcontextx
+function saves the current execution context in the newly allocated structure
+.Vt ucontext_t ,
+which is returned on success.
+If architecture defines additional CPU states that can be stored in extended
+blocks referenced from the
+.Vt ucontext_t ,
+the memory for them may be allocated and their context also stored.
+Memory returned by
+.Fn getcontextx
+function shall be freed using
+.Fn free 3 .
+.Pp
+The
 .Fn setcontext
 function
 makes a previously saved thread context the current thread context, i.e.,
@@ -109,11 +123,24 @@ If successful,
 returns zero and
 .Fn setcontext
 does not return; otherwise \-1 is returned.
+The
+.Fn getcontextx
+returns pointer to the allocated and initialized context on success, and
+.Va NULL
+on failure.
 .Sh ERRORS
 No errors are defined for
 .Fn getcontext
 or
 .Fn setcontext .
+The
+.Fn getcontextx
+may return the following errors in
+.Va errno :
+.Bl -tag -width Er
+.It Bq Er ENOMEM
+No memory was available to allocate for the context or some extended state.
+.El
 .Sh SEE ALSO
 .Xr sigaction 2 ,
 .Xr sigaltstack 2 ,
diff --git a/lib/libc/gen/ucontext.3 b/lib/libc/gen/ucontext.3
index 0574322..69ecbc1 100644
--- a/lib/libc/gen/ucontext.3
+++ b/lib/libc/gen/ucontext.3
@@ -92,6 +92,9 @@ structures:
 .Ft int
 .Fn getcontext "ucontext_t *" ;
 .It
+.Ft "ucontext_t *"
+.Fn getcontextx "void" ;
+.It
 .Ft int
 .Fn setcontext "const ucontext_t *" ;
 .It
@@ -104,4 +107,5 @@ structures:
 .Sh SEE ALSO
 .Xr sigaltstack 2 ,
 .Xr getcontext 3 ,
+.Xr getcontextx 3 ,
 .Xr makecontext 3