kernel: add per-thread errno support

Saves an errno per-thread, retrieved via _get_errno(), instead of
changing the value of a global variable during context switches to avoid
a hit to the context switch performance.

Per-arch asm implementations are provided for maximum performance.

Enabled by default, but can be disabled via the CONFIG_ERRNO option.

Change-Id: I81d57a2e318c94c68eee913ae0d4ca3a3609c7a4
Signed-off-by: Benjamin Walsh <benjamin.walsh@windriver.com>

arch/arc/core/Makefile

@@ -13,3 +13,4 @@ obj-y += prep_c.o \
          vector_table.o
 
 obj-$(CONFIG_IRQ_OFFLOAD) += irq_offload.o
+obj-$(CONFIG_ERRNO) += errno.o

arch/arc/core/errno.S

@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 2015 Wind River Systems, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/** @file
+ *
+ * @brief Per-thread errno accessor function
+ *
+ * Allow accessing the errno for the current thread without involving the
+ * context switching.
+ */
+
+#define _ASMLANGUAGE
+
+#include <nano_private.h>
+#include <offsets.h>
+
+GTEXT(_nanokernel)
+GTEXT(_get_errno)
+
+SECTION_FUNC(TEXT, _get_errno)
+
+	mov_s r0, _nanokernel
+	ld_s r0, [r0, __tNANO_current_OFFSET]
+	add_s r0, r0, __tTCS_errno_var_OFFSET
+	j_s.nd [blink]
+	nop_s

arch/arc/include/nano_private.h

@@ -180,6 +180,9 @@ struct tcs {
 #ifdef CONFIG_NANO_TIMEOUTS
 	struct _nano_timeout nano_timeout;
 #endif
+#ifdef CONFIG_ERRNO
+	int errno_var;
+#endif
 };
 
 struct s_NANO {

arch/arm/core/cortex_m/Makefile

@@ -6,3 +6,5 @@ asflags-y = $(ccflags-y)
 obj-y = vector_table.o reset.o \
 	prep_c.o scs.o scb.o nmi.o \
 	sw_isr_table.o
+
+obj-$(CONFIG_ERRNO) += errno.o

arch/arm/core/cortex_m/errno.S

@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2015 Wind River Systems, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/** @file
+ *
+ * @brief Per-thread errno accessor function
+ *
+ * Allow accessing the errno for the current thread without involving the
+ * context switching.
+ */
+
+#define _ASMLANGUAGE
+
+#include <nano_private.h>
+#include <offsets.h>	/* nanokernel structure offset definitions */
+
+_ASM_FILE_PROLOGUE
+
+GTEXT(_nanokernel)
+GTEXT(_get_errno)
+
+SECTION_FUNC(TEXT, _get_errno)
+
+	ldr r0, =_nanokernel
+	ldr r0, [r0, #__tNANO_current_OFFSET]
+	adds.n r0, #__tTCS_errno_var_OFFSET
+	bx lr

arch/arm/include/nano_private.h

@@ -125,6 +125,9 @@ struct tcs {
 #ifdef CONFIG_NANO_TIMEOUTS
 	struct _nano_timeout nano_timeout;
 #endif
+#ifdef CONFIG_ERRNO
+	int errno_var;
+#endif
 };
 
 struct s_NANO {

arch/x86/core/Makefile

@@ -22,4 +22,4 @@ obj-y += gdt.o fatal.o cpuhalt.o \
 obj-$(CONFIG_IRQ_OFFLOAD) += irq_offload.o
 obj-$(CONFIG_FP_SHARING) += float.o
 obj-$(CONFIG_MICROKERNEL) += strtask.o
-
+obj-$(CONFIG_ERRNO) += errno.o

arch/x86/core/errno.S

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2015 Wind River Systems, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/** @file
+ *
+ * @brief Per-thread errno accessor function
+ *
+ * Allow accessing the errno for the current thread without involving the
+ * context switching.
+ */
+
+#define _ASMLANGUAGE
+
+#include <nano_private.h>
+#include <arch/x86/asm.h>
+#include <offsets.h>
+
+GTEXT(_nanokernel)
+GTEXT(_get_errno)
+
+SECTION_FUNC(TEXT, _get_errno)
+
+	movl _nanokernel + __tNANO_current_OFFSET, %eax
+	addl $__tTCS_errno_var_OFFSET, %eax
+	ret

arch/x86/include/nano_private.h

@@ -663,6 +663,10 @@ struct tcs {
 	struct _nano_timeout nano_timeout;
 #endif
 
+#ifdef CONFIG_ERRNO
+	int errno_var;
+#endif
+
 	/*
 	 * The location of all floating point related structures/fields MUST be
 	 * located at the end of struct tcs.  This way only the

kernel/nanokernel/Kconfig

@@ -82,4 +82,13 @@ config  NANO_TIMERS
 	help
 	Allow fibers and tasks to wait on nanokernel timers, which can be
 	accessed using the nano_timer_xxx() APIs.
+
+config ERRNO
+	bool
+	prompt "Enable errno support"
+	default y
+	help
+	Enable per-thread errno in the kernel. Application and library code must
+	include errno.h provided by the C library (libc) to use the errno symbol.
+	The C library must access the per-thread errno via the _get_errno() symbol.
 endmenu

kernel/nanokernel/include/nano_offsets.h

@@ -56,6 +56,9 @@ GEN_OFFSET_SYM(tTCS, preempReg); /* start of prempt register set */
 GEN_OFFSET_SYM(tTCS, next_thread);
 #endif
 
+#ifdef CONFIG_ERRNO
+GEN_OFFSET_SYM(tTCS, errno_var);
+#endif
 
 /* size of the entire struct tcs structure */