libc/string: prevent libc in the kernel/userspace optionally

Add the `LIBC_PREVENT_STRING_KERNEL` and `LIBC_PREVENT_STRING_USER` that are meant to be selected by the chip if no libc implementation is going to be built. If selected, neither NuttX's software version of the libc nor any architecture-specific implementation will be built in the kernel or in the userspace, respectively. In this case, the linker may provide a ROM-defined version of the libc functions instead.
2025-01-13 13:18:50 +08:00 · 2023-04-28 13:55:23 -03:00 · 2023-04-28 13:55:23 -03:00 · 58e97e521c
commit 58e97e521c
parent 6be363ff35
73 changed files with 405 additions and 76 deletions
--- a/libs/libc/Makefile
+++ b/libs/libc/Makefile
@ -82,6 +82,7 @@ else
 endif

 CFLAGS += ${INCDIR_PREFIX}$(TOPDIR)$(DELIM)libs$(DELIM)libc
+AFLAGS += ${INCDIR_PREFIX}$(TOPDIR)$(DELIM)libs$(DELIM)libc

 # Rule for the symbol table generation

--- a/libs/libc/libc.h
+++ b/libs/libc/libc.h
@ -27,15 +27,17 @@

 #include <nuttx/config.h>

-#include <sys/types.h>
-#include <stdbool.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <limits.h>
-#include <semaphore.h>
+#ifndef __ASSEMBLY__
+#  include <sys/types.h>
+#  include <stdbool.h>
+#  include <stdio.h>
+#  include <stdlib.h>
+#  include <limits.h>
+#  include <semaphore.h>

-#include <nuttx/lib/lib.h>
-#include <nuttx/streams.h>
+#  include <nuttx/lib/lib.h>
+#  include <nuttx/streams.h>
+#endif

 /****************************************************************************
 * Pre-processor Definitions
@ -53,6 +55,12 @@

 #define LIB_BUFLEN_UNKNOWN INT_MAX

+#if defined(CONFIG_BUILD_FLAT) || \
+    ((!defined(CONFIG_LIBC_PREVENT_STRING_USER) && !defined(__KERNEL__))  || \
+     (!defined(CONFIG_LIBC_PREVENT_STRING_KERNEL) && defined(__KERNEL__)))
+#  define LIBC_BUILD_STRING
+#endif
+
 /****************************************************************************
 * Public Types
 ****************************************************************************/
@ -61,6 +69,8 @@
 * Public Data
 ****************************************************************************/

+#ifndef __ASSEMBLY__
+
 #undef EXTERN
 #if defined(__cplusplus)
 #define EXTERN extern "C"
@ -157,4 +167,6 @@ void lib_cxx_initialize(void);
 }
 #endif

+#endif /* __ASSEMBLY__ */
+
 #endif /* __LIBS_LIBC_LIBC_H */
--- a/libs/libc/machine/Kconfig
+++ b/libs/libc/machine/Kconfig
@ -137,6 +137,30 @@ config LIBC_ARCH_ELF_64BIT
 	default n
 	depends on LIBC_ARCH_ELF

+config LIBC_PREVENT_STRING_KERNEL
+	bool
+	default n
+	---help---
+		Prevent any implementation of the libc from being built and linked
+		in the kernel, including NuttX's software-defined version of the libc
+		or any other architecture-specific version of it. The ROM-defined
+		version should be linked instead. This option is particularly useful
+		when it's required that the ROM-defined libc to be used by the kernel
+		(for accessing some driver resource, for instance) but the userspace
+		is forbidden to use the same ROM-defined versions. In this case,
+		NuttX's software-defined version of the libc or arch-specific
+		assembly version is built instead.
+
+config LIBC_PREVENT_STRING_USER
+	bool
+	default n
+	---help---
+		Prevent any implementation of the libc from being built and linked
+		in the userspace, including NuttX's software-defined version of the
+		libc or any other architecture-specific version of it. A ROM-defined
+		version of the libc may be linked to the userspace by the linker.
+
+
 # One or more the of above may be selected by architecture specific logic

 if ARCH_ARM
--- a/libs/libc/machine/arm/armv7-a/gnu/arch_memchr.S
+++ b/libs/libc/machine/arm/armv7-a/gnu/arch_memchr.S
@ -66,6 +66,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
@ 2011-02-07 david.gilbert@linaro.org
@    Extracted from local git a5b438d861
@ 2011-07-14 david.gilbert@linaro.org
@ -389,3 +393,5 @@ memchr:
 #else
  /* Defined in memchr-stub.c.  */
 #endif
+
+#endif
--- a/libs/libc/machine/arm/armv7-a/gnu/arch_memcpy.S
+++ b/libs/libc/machine/arm/armv7-a/gnu/arch_memcpy.S
@ -33,6 +33,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /*
 * This memcpy routine is optimised for Cortex-A15 cores and takes advantage
 * of VFP or NEON when built with the appropriate flags.
@ -624,3 +628,5 @@ def_fn memcpy p2align=6
 	bx	lr

 	.size	memcpy, . - memcpy
+
+#endif
--- a/libs/libc/machine/arm/armv7-a/gnu/arch_memmove.S
+++ b/libs/libc/machine/arm/armv7-a/gnu/arch_memmove.S
@ -29,6 +29,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 	.thumb
 	.syntax unified
 	.global memmove
@ -64,3 +68,5 @@ memmove:
 	pop	{r4}
 	bx	lr
 	.size memmove, . - memmove
+
+#endif
--- a/libs/libc/machine/arm/armv7-a/gnu/arch_memset.S
+++ b/libs/libc/machine/arm/armv7-a/gnu/arch_memset.S
@ -29,6 +29,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 	.arm
 	.syntax unified
 	.global memset
@ -144,3 +148,5 @@ memset:
 	strbcs      r1, [r3], #1
 	bx          lr
 	.size memset, . - memset
+
+#endif
--- a/libs/libc/machine/arm/armv7-a/gnu/arch_strcmp.S
+++ b/libs/libc/machine/arm/armv7-a/gnu/arch_strcmp.S
@ -30,6 +30,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 #ifdef __ARMEB__
 #define SHFT2LSB lsl
 #define SHFT2LSBEQ lsleq
@ -301,3 +305,5 @@ strcmp:
 	ldr	r5, [sp], #4
 	bx	lr
 	.size strcmp, . - strcmp
+
+#endif
--- a/libs/libc/machine/arm/armv7-a/gnu/arch_strlen.S
+++ b/libs/libc/machine/arm/armv7-a/gnu/arch_strlen.S
@ -62,6 +62,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 #include "acle-compat.h"

 	.macro def_fn f p2align=0
@ -182,3 +186,5 @@ def_fn	strlen p2align=6
 	mov	const_0, #0
 	b	.Lstart_realigned
 	.size	strlen, . - strlen
+
+#endif
--- a/libs/libc/machine/arm/armv7-m/gnu/arch_memchr.S
+++ b/libs/libc/machine/arm/armv7-m/gnu/arch_memchr.S
@ -66,6 +66,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
@ 2011-02-07 david.gilbert@linaro.org
@    Extracted from local git a5b438d861
@ 2011-07-14 david.gilbert@linaro.org
@ -427,3 +431,5 @@ memchr:
 #else
  /* Defined in memchr-stub.c.  */
 #endif
+
+#endif
--- a/libs/libc/machine/arm/armv7-m/gnu/arch_memcpy.S
+++ b/libs/libc/machine/arm/armv7-m/gnu/arch_memcpy.S
@ -29,6 +29,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /* This memcpy routine is optimised for Cortex-M3/M4 cores with/without
   unaligned access.

@ -345,3 +349,5 @@ memcpy:
 	.cantunwind
 	.fnend
 	.size	memcpy, .-memcpy
+
+#endif
--- a/libs/libc/machine/arm/armv7-m/gnu/arch_memmove.S
+++ b/libs/libc/machine/arm/armv7-m/gnu/arch_memmove.S
@ -29,6 +29,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 #include "arm_asm.h"

 	.thumb
@ -71,3 +75,5 @@ memmove:
 	.cantunwind
 	.fnend
 	.size memmove, . - memmove
+
+#endif
--- a/libs/libc/machine/arm/armv7-m/gnu/arch_memset.S
+++ b/libs/libc/machine/arm/armv7-m/gnu/arch_memset.S
@ -29,6 +29,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 #include "arm_asm.h"

 	.thumb
@ -114,3 +118,5 @@ memset:
 	.cantunwind
 	.fnend
 	.size memset, . - memset
+
+#endif
--- a/libs/libc/machine/arm/armv7-m/gnu/arch_strcmp.S
+++ b/libs/libc/machine/arm/armv7-m/gnu/arch_strcmp.S
@ -29,6 +29,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /* Very similar to the generic code, but uses Thumb2 as implemented
   in ARMv7-M.  */

@ -419,3 +423,5 @@ def_fn strcmp
 	.cantunwind
 	.fnend
 	.size strcmp, . - strcmp
+
+#endif
--- a/libs/libc/machine/arm/armv7-m/gnu/arch_strcpy.S
+++ b/libs/libc/machine/arm/armv7-m/gnu/arch_strcpy.S
@ -18,6 +18,10 @@
 *
 ***************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /* This strcpy borrowed some ideas from arch_strcmp.S(). */

 /* Parameters and result. */
@ -306,3 +310,4 @@ offset_3:
    *dst++ = 0;
 #endif  /* Pseudo code end */

+#endif
--- a/libs/libc/machine/arm/armv7-m/gnu/arch_strlen.S
+++ b/libs/libc/machine/arm/armv7-m/gnu/arch_strlen.S
@ -62,6 +62,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 #include "arm-acle-compat.h"
 #include "arm_asm.h"

@ -193,3 +197,5 @@ def_fn	strlen p2align=6
 	.cantunwind
 	.fnend
 	.size	strlen, . - strlen
+
+#endif
--- a/libs/libc/machine/arm/armv7-r/gnu/arch_memchr.S
+++ b/libs/libc/machine/arm/armv7-r/gnu/arch_memchr.S
@ -66,6 +66,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
@ 2011-02-07 david.gilbert@linaro.org
@    Extracted from local git a5b438d861
@ 2011-07-14 david.gilbert@linaro.org
@ -389,3 +393,5 @@ memchr:
 #else
  /* Defined in memchr-stub.c.  */
 #endif
+
+#endif
--- a/libs/libc/machine/arm/armv7-r/gnu/arch_memcpy.S
+++ b/libs/libc/machine/arm/armv7-r/gnu/arch_memcpy.S
@ -33,6 +33,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /*
 * This memcpy routine is optimised for Cortex-A15 cores and takes advantage
 * of VFP or NEON when built with the appropriate flags.
@ -624,3 +628,5 @@ def_fn memcpy p2align=6
 	bx	lr

 	.size	memcpy, . - memcpy
+
+#endif
--- a/libs/libc/machine/arm/armv7-r/gnu/arch_memmove.S
+++ b/libs/libc/machine/arm/armv7-r/gnu/arch_memmove.S
@ -29,6 +29,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 	.thumb
 	.syntax unified
 	.global memmove
@ -64,3 +68,5 @@ memmove:
 	pop	{r4}
 	bx	lr
 	.size memmove, . - memmove
+
+#endif
--- a/libs/libc/machine/arm/armv7-r/gnu/arch_memset.S
+++ b/libs/libc/machine/arm/armv7-r/gnu/arch_memset.S
@ -29,6 +29,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 	.arm
 	.syntax unified
 	.global memset
@ -144,3 +148,5 @@ memset:
 	strbcs      r1, [r3], #1
 	bx          lr
 	.size memset, . - memset
+
+#endif
--- a/libs/libc/machine/arm/armv7-r/gnu/arch_strcmp.S
+++ b/libs/libc/machine/arm/armv7-r/gnu/arch_strcmp.S
@ -30,6 +30,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 #ifdef __ARMEB__
 #define SHFT2LSB lsl
 #define SHFT2LSBEQ lsleq
@ -301,3 +305,5 @@ strcmp:
 	ldr	r5, [sp], #4
 	bx	lr
 	.size strcmp, . - strcmp
+
+#endif
--- a/libs/libc/machine/arm/armv7-r/gnu/arch_strlen.S
+++ b/libs/libc/machine/arm/armv7-r/gnu/arch_strlen.S
@ -62,6 +62,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 #include "acle-compat.h"

 	.macro def_fn f p2align=0
@ -182,3 +186,5 @@ def_fn	strlen p2align=6
 	mov	const_0, #0
 	b	.Lstart_realigned
 	.size	strlen, . - strlen
+
+#endif
--- a/libs/libc/machine/arm/armv8-m/gnu/arch_memchr.S
+++ b/libs/libc/machine/arm/armv8-m/gnu/arch_memchr.S
@ -66,6 +66,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
@ 2011-02-07 david.gilbert@linaro.org
@    Extracted from local git a5b438d861
@ 2011-07-14 david.gilbert@linaro.org
@ -427,3 +431,5 @@ memchr:
 #else
  /* Defined in memchr-stub.c.  */
 #endif
+
+#endif
--- a/libs/libc/machine/arm/armv8-m/gnu/arch_memcpy.S
+++ b/libs/libc/machine/arm/armv8-m/gnu/arch_memcpy.S
@ -29,6 +29,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /* This memcpy routine is optimised for Cortex-M3/M4 cores with/without
   unaligned access.

@ -367,3 +371,5 @@ memcpy:
 	.cantunwind
 	.fnend
 	.size	memcpy, .-memcpy
+
+#endif
--- a/libs/libc/machine/arm/armv8-m/gnu/arch_memmove.S
+++ b/libs/libc/machine/arm/armv8-m/gnu/arch_memmove.S
@ -29,6 +29,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 #include "arm_asm.h"

 	.thumb
@ -71,3 +75,5 @@ memmove:
 	.cantunwind
 	.fnend
 	.size memmove, . - memmove
+
+#endif
--- a/libs/libc/machine/arm/armv8-m/gnu/arch_memset.S
+++ b/libs/libc/machine/arm/armv8-m/gnu/arch_memset.S
@ -29,6 +29,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 #include "arm_asm.h"

 	.thumb
@ -129,3 +133,5 @@ memset:
 	.cantunwind
 	.fnend
 	.size memset, . - memset
+
+#endif
--- a/libs/libc/machine/arm/armv8-m/gnu/arch_strcmp.S
+++ b/libs/libc/machine/arm/armv8-m/gnu/arch_strcmp.S
@ -29,6 +29,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /* Very similar to the generic code, but uses Thumb2 as implemented
   in ARMv7-M.  */

@ -419,3 +423,5 @@ def_fn strcmp
 	.cantunwind
 	.fnend
 	.size strcmp, . - strcmp
+
+#endif
--- a/libs/libc/machine/arm/armv8-m/gnu/arch_strlen.S
+++ b/libs/libc/machine/arm/armv8-m/gnu/arch_strlen.S
@ -62,6 +62,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 #include "arm-acle-compat.h"
 #include "arm_asm.h"

@ -193,3 +197,5 @@ def_fn	strlen p2align=6
 	.cantunwind
 	.fnend
 	.size	strlen, . - strlen
+
+#endif
--- a/libs/libc/machine/arm64/gnu/arch_memchr.S
+++ b/libs/libc/machine/arm64/gnu/arch_memchr.S
@ -29,6 +29,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /* Assumptions:
 *
 * ARMv8-a, AArch64
@ -171,3 +175,5 @@ def_fn memchr
 	ret

 	.size	memchr, . - memchr
+
+#endif
--- a/libs/libc/machine/arm64/gnu/arch_memcmp.S
+++ b/libs/libc/machine/arm64/gnu/arch_memcmp.S
@ -59,6 +59,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /* Assumptions:
 *
 * ARMv8-a, AArch64, unaligned accesses.
@ -194,3 +198,5 @@ L(byte_loop):
 	ret

 	.size	memcmp, . - memcmp
+
+#endif
--- a/libs/libc/machine/arm64/gnu/arch_memcpy.S
+++ b/libs/libc/machine/arm64/gnu/arch_memcpy.S
@ -59,6 +59,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /* Assumptions:
 *
 * ARMv8-a, AArch64, unaligned accesses.
@ -230,3 +234,5 @@ L(copy_long):
 	ret

 	.size	memcpy, . - memcpy
+
+#endif
--- a/libs/libc/machine/arm64/gnu/arch_memmove.S
+++ b/libs/libc/machine/arm64/gnu/arch_memmove.S
@ -59,6 +59,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /* Assumptions:
 *
 * ARMv8-a, AArch64, unaligned accesses
@ -155,3 +159,5 @@ def_fn memmove, 6
 3:	ret

 	.size	memmove, . - memmove
+
+#endif
--- a/libs/libc/machine/arm64/gnu/arch_memset.S
+++ b/libs/libc/machine/arm64/gnu/arch_memset.S
@ -59,6 +59,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /* Assumptions:
 *
 * ARMv8-a, AArch64, unaligned accesses
@ -240,3 +244,5 @@ L(zva_other):
 	b	L(tail64)

 	.size	memset, . - memset
+
+#endif
--- a/libs/libc/machine/arm64/gnu/arch_strchr.S
+++ b/libs/libc/machine/arm64/gnu/arch_strchr.S
@ -29,6 +29,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /* Assumptions:
 *
 * ARMv8-a, AArch64
@ -159,3 +163,5 @@ def_fn strchr
 	ret

 	.size	strchr, . - strchr
+
+#endif
--- a/libs/libc/machine/arm64/gnu/arch_strchrnul.S
+++ b/libs/libc/machine/arm64/gnu/arch_strchrnul.S
@ -29,6 +29,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /* Assumptions:
 *
 * ARMv8-a, AArch64
@ -144,3 +148,5 @@ def_fn strchrnul
 	ret

 	.size	strchrnul, . - strchrnul
+
+#endif
--- a/libs/libc/machine/arm64/gnu/arch_strcmp.S
+++ b/libs/libc/machine/arm64/gnu/arch_strcmp.S
@ -33,6 +33,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /* Assumptions:
 *
 * ARMv8-a, AArch64
@ -203,3 +207,5 @@ L(done):
 	sub	result, data1, data2
 	ret
 	.size	strcmp, .-strcmp
+
+#endif
--- a/libs/libc/machine/arm64/gnu/arch_strcpy.S
+++ b/libs/libc/machine/arm64/gnu/arch_strcpy.S
@ -29,6 +29,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /* Assumptions:
 *
 * ARMv8-a, AArch64, unaligned accesses, min page size 4k.
@ -336,3 +340,5 @@ def_fn STRCPY p2align=6
 	b	.Lfp_gt8

 	.size	STRCPY, . - STRCPY
+
+#endif
--- a/libs/libc/machine/arm64/gnu/arch_strlen.S
+++ b/libs/libc/machine/arm64/gnu/arch_strlen.S
@ -33,6 +33,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /* Assumptions:
 *
 * ARMv8-a, AArch64, unaligned accesses, min page size 4k.
@ -240,3 +244,5 @@ L(page_cross):
 	b	L(page_cross_entry)

 	.size	strlen, . - strlen
+
+#endif
--- a/libs/libc/machine/arm64/gnu/arch_strncmp.S
+++ b/libs/libc/machine/arm64/gnu/arch_strncmp.S
@ -33,6 +33,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /* Assumptions:
 *
 * ARMv8-a, AArch64
@ -292,3 +296,5 @@ def_fn strncmp
 	mov	result, #0
 	ret
 	.size strncmp, . - strncmp
+
+#endif
--- a/libs/libc/machine/arm64/gnu/arch_strnlen.S
+++ b/libs/libc/machine/arm64/gnu/arch_strnlen.S
@ -33,6 +33,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /* Assumptions:
 *
 * ARMv8-a, AArch64
@ -186,3 +190,5 @@ def_fn strnlen
 	csel	data2, data2, data2a, le
 	b	.Lrealigned
 	.size	strnlen, . - .Lstart	/* Include pre-padding in size.  */
+
+#endif
--- a/libs/libc/machine/arm64/gnu/arch_strrchr.S
+++ b/libs/libc/machine/arm64/gnu/arch_strrchr.S
@ -29,6 +29,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /* Assumptions:
 *
 * ARMv8-a, AArch64
@ -177,3 +181,5 @@ def_fn strrchr
 	ret

 	.size	strrchr, . - strrchr
+
+#endif
--- a/libs/libc/machine/risc-v/gnu/arch_memcpy.S
+++ b/libs/libc/machine/risc-v/gnu/arch_memcpy.S
@ -18,6 +18,14 @@
 *
 ****************************************************************************/

+/************************************************************************************
+ * Included Files
+ ************************************************************************************/
+
+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /************************************************************************************
 * Public Symbols
 ************************************************************************************/
@ -128,3 +136,5 @@ memcpy:
 	bltu		a1, a3, 5b
 6:
 	ret
+
+#endif
--- a/libs/libc/machine/risc-v/gnu/arch_memset.S
+++ b/libs/libc/machine/risc-v/gnu/arch_memset.S
@ -13,6 +13,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 .text
 .global memset
 .type	memset, @function
@ -104,3 +108,5 @@ memset:
 	bleu a2, t1, .Ltiny
 	j .Laligned
 	.size	memset, .-memset
+
+#endif
--- a/libs/libc/machine/risc-v/gnu/arch_strcmp.S
+++ b/libs/libc/machine/risc-v/gnu/arch_strcmp.S
@ -13,6 +13,10 @@
 *
 ****************************************************************************/

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 #include "asm.h"

 .text
@ -185,3 +189,5 @@ strcmp:
 mask:
 .dword 0x7f7f7f7f7f7f7f7f
 #endif
+
+#endif
--- a/libs/libc/machine/xtensa/arch_memcpy.S
+++ b/libs/libc/machine/xtensa/arch_memcpy.S
@ -27,6 +27,10 @@
 #include <arch/chip/core-isa.h>
 #include <arch/xtensa/xtensa_abi.h>

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /****************************************************************************
 * Pre-processor Macros
 ****************************************************************************/
@ -276,3 +280,5 @@ __memcpy_aux:
  .end schedule

  .size memcpy, . - memcpy
+
+#endif
--- a/libs/libc/machine/xtensa/arch_memmove.S
+++ b/libs/libc/machine/xtensa/arch_memmove.S
@ -27,6 +27,10 @@
 #include <arch/chip/core-isa.h>
 #include <arch/xtensa/xtensa_abi.h>

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /****************************************************************************
 * Pre-processor Macros
 ****************************************************************************/
@ -479,3 +483,5 @@ memmove:

  .end schedule
  .size memmove, . - memmove
+
+#endif
--- a/libs/libc/machine/xtensa/arch_memset.S
+++ b/libs/libc/machine/xtensa/arch_memset.S
@ -27,6 +27,10 @@
 #include <arch/chip/core-isa.h>
 #include <arch/xtensa/xtensa_abi.h>

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/
@ -175,3 +179,5 @@ __memset_aux:
 	.end schedule

 	.size	memset, . - memset
+
+#endif
--- a/libs/libc/machine/xtensa/arch_strcmp.S
+++ b/libs/libc/machine/xtensa/arch_strcmp.S
@ -27,6 +27,10 @@
 #include <arch/chip/core-isa.h>
 #include <arch/xtensa/xtensa_abi.h>

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /****************************************************************************
 * Pre-processor Macros
 ****************************************************************************/
@ -760,3 +764,4 @@ strcmp:
  .end  schedule
  .size strcmp, . - strcmp

+#endif
--- a/libs/libc/machine/xtensa/arch_strcpy.S
+++ b/libs/libc/machine/xtensa/arch_strcpy.S
@ -27,6 +27,10 @@
 #include <arch/chip/core-isa.h>
 #include <arch/xtensa/xtensa_abi.h>

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/
@ -240,3 +244,5 @@ strcpy:
  .end schedule

  .size strcpy, . - strcpy
+
+#endif
--- a/libs/libc/machine/xtensa/arch_strlen.S
+++ b/libs/libc/machine/xtensa/arch_strlen.S
@ -27,6 +27,10 @@
 #include <arch/chip/core-isa.h>
 #include <arch/xtensa/xtensa_abi.h>

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/
@ -120,3 +124,5 @@ strlen:
  .end schedule

  .size strlen, . - strlen
+
+#endif
--- a/libs/libc/machine/xtensa/arch_strncpy.S
+++ b/libs/libc/machine/xtensa/arch_strncpy.S
@ -27,6 +27,10 @@
 #include <arch/chip/core-isa.h>
 #include <arch/xtensa/xtensa_abi.h>

+#include "libc.h"
+
+#ifdef LIBC_BUILD_STRING
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/
@ -261,3 +265,5 @@ strncpy:
 .end schedule

  .size strncpy, . - strncpy
+
+#endif
--- a/libs/libc/string/Make.defs
+++ b/libs/libc/string/Make.defs
@ -32,61 +32,15 @@ CSRCS += lib_strsep.c lib_strerrorr.c lib_explicit_bzero.c lib_strsignal.c
 CSRCS += lib_index.c lib_rindex.c lib_timingsafe_bcmp.c lib_strverscmp.c
 CSRCS += lib_mempcpy.c lib_rawmemchr.c lib_bzero.c

-ifneq ($(CONFIG_LIBC_ARCH_MEMCHR),y)
-CSRCS += lib_memchr.c
-endif
+CSRCS += lib_memchr.c lib_memcmp.c lib_memmove.c lib_memset.c
+CSRCS += lib_strchr.c lib_strcmp.c lib_strcpy.c lib_strlcat.c
+CSRCS += lib_strlcpy.c lib_strlen.c lib_strncpy.c lib_strnlen.c

-ifneq ($(CONFIG_LIBC_ARCH_MEMCMP),y)
-CSRCS += lib_memcmp.c
-endif
-
-ifneq ($(CONFIG_LIBC_ARCH_MEMCPY),y)
 ifeq ($(CONFIG_MEMCPY_VIK),y)
 CSRCS += lib_vikmemcpy.c
 else
 CSRCS += lib_memcpy.c
 endif
-endif
-
-ifneq ($(CONFIG_LIBC_ARCH_MEMMOVE),y)
-CSRCS += lib_memmove.c
-endif
-
-ifneq ($(CONFIG_LIBC_ARCH_MEMSET),y)
-CSRCS += lib_memset.c
-endif
-
-ifneq ($(CONFIG_LIBC_ARCH_STRCHR),y)
-CSRCS += lib_strchr.c
-endif
-
-ifneq ($(CONFIG_LIBC_ARCH_STRCMP),y)
-CSRCS += lib_strcmp.c
-endif
-
-ifneq ($(CONFIG_LIBC_ARCH_STRCPY),y)
-CSRCS += lib_strcpy.c
-endif
-
-ifneq ($(CONFIG_LIBC_ARCH_STRLCAT),y)
-CSRCS += lib_strlcat.c
-endif
-
-ifneq ($(CONFIG_LIBC_ARCH_STRLCPY),y)
-CSRCS += lib_strlcpy.c
-endif
-
-ifneq ($(CONFIG_LIBC_ARCH_STRLEN),y)
-CSRCS += lib_strlen.c
-endif
-
-ifneq ($(CONFIG_LIBC_ARCH_STRNCPY),y)
-CSRCS += lib_strncpy.c
-endif
-
-ifneq ($(CONFIG_LIBC_ARCH_STRNLEN),y)
-CSRCS += lib_strnlen.c
-endif

 ifeq ($(CONFIG_LIBC_LOCALE),y)
 CSRCS += lib_strcoll.c lib_strxfrm.c
--- a/libs/libc/string/lib_memchr.c
+++ b/libs/libc/string/lib_memchr.c
@ -26,6 +26,8 @@

 #include <string.h>

+#include "libc.h"
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/
@ -44,6 +46,7 @@
 *
 ****************************************************************************/

+#if !defined(CONFIG_LIBC_ARCH_MEMCHR) && defined(LIBC_BUILD_STRING)
 #undef memchr /* See mm/README.txt */
 FAR void *memchr(FAR const void *s, int c, size_t n)
 {
@ -61,3 +64,4 @@ FAR void *memchr(FAR const void *s, int c, size_t n)

  return NULL;
 }
+#endif
--- a/libs/libc/string/lib_memcmp.c
+++ b/libs/libc/string/lib_memcmp.c
@ -26,11 +26,13 @@
 #include <sys/types.h>
 #include <string.h>

+#include "libc.h"
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/

-#ifndef CONFIG_LIBC_ARCH_MEMCMP
+#if !defined(CONFIG_LIBC_ARCH_MEMCMP) && defined(LIBC_BUILD_STRING)
 #undef memcmp /* See mm/README.txt */
 no_builtin("memcmp")
 int memcmp(FAR const void *s1, FAR const void *s2, size_t n)
--- a/libs/libc/string/lib_memcpy.c
+++ b/libs/libc/string/lib_memcpy.c
@ -26,6 +26,8 @@
 #include <sys/types.h>
 #include <string.h>

+#include "libc.h"
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/
@ -34,7 +36,7 @@
 * Name: memcpy
 ****************************************************************************/

-#ifndef CONFIG_LIBC_ARCH_MEMCPY
+#if !defined(CONFIG_LIBC_ARCH_MEMCPY) && defined(LIBC_BUILD_STRING)
 #undef memcpy /* See mm/README.txt */
 no_builtin("memcpy")
 FAR void *memcpy(FAR void *dest, FAR const void *src, size_t n)
--- a/libs/libc/string/lib_memmove.c
+++ b/libs/libc/string/lib_memmove.c
@ -26,11 +26,13 @@
 #include <sys/types.h>
 #include <string.h>

+#include "libc.h"
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/

-#ifndef CONFIG_LIBC_ARCH_MEMMOVE
+#if !defined(CONFIG_LIBC_ARCH_MEMMOVE) && defined(LIBC_BUILD_STRING)
 #undef memmove /* See mm/README.txt */
 no_builtin("memmove")
 FAR void *memmove(FAR void *dest, FAR const void *src, size_t count)
--- a/libs/libc/string/lib_memset.c
+++ b/libs/libc/string/lib_memset.c
@ -30,6 +30,8 @@
 #include <string.h>
 #include <assert.h>

+#include "libc.h"
+
 /****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/
@ -46,7 +48,7 @@
 * Public Functions
 ****************************************************************************/

-#ifndef CONFIG_LIBC_ARCH_MEMSET
+#if !defined(CONFIG_LIBC_ARCH_MEMSET) && defined(LIBC_BUILD_STRING)
 #undef memset /* See mm/README.txt */
 no_builtin("memset")
 FAR void *memset(FAR void *s, int c, size_t n)
--- a/libs/libc/string/lib_strcasecmp.c
+++ b/libs/libc/string/lib_strcasecmp.c
@ -27,11 +27,13 @@
 #include <strings.h>
 #include <ctype.h>

+#include "libc.h"
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/

-#ifndef CONFIG_LIBC_ARCH_STRCASECMP
+#if !defined(CONFIG_LIBC_ARCH_STRCASECMP) && defined(LIBC_BUILD_STRING)
 #undef strcasecmp /* See mm/README.txt */
 int strcasecmp(FAR const char *cs, FAR const char *ct)
 {
--- a/libs/libc/string/lib_strcat.c
+++ b/libs/libc/string/lib_strcat.c
@ -26,11 +26,13 @@

 #include <string.h>

+#include "libc.h"
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/

-#ifndef CONFIG_LIBC_ARCH_STRCAT
+#if !defined(CONFIG_LIBC_ARCH_STRCAT) && defined(LIBC_BUILD_STRING)
 #undef strcat /* See mm/README.txt */
 FAR char *strcat(FAR char *dest, FAR const char *src)
 {
--- a/libs/libc/string/lib_strchr.c
+++ b/libs/libc/string/lib_strchr.c
@ -26,6 +26,8 @@

 #include <string.h>

+#include "libc.h"
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/
@ -44,7 +46,7 @@
 *
 ****************************************************************************/

-#ifndef CONFIG_LIBC_ARCH_STRCHR
+#if !defined(CONFIG_LIBC_ARCH_STRCHR) && defined(LIBC_BUILD_STRING)
 #undef strchr /* See mm/README.txt */
 FAR char *strchr(FAR const char *s, int c)
 {
--- a/libs/libc/string/lib_strchrnul.c
+++ b/libs/libc/string/lib_strchrnul.c
@ -26,6 +26,8 @@

 #include <string.h>

+#include "libc.h"
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/
@ -44,7 +46,7 @@
 *
 ****************************************************************************/

-#ifndef CONFIG_LIBC_ARCH_STRCHRNUL
+#if !defined(CONFIG_LIBC_ARCH_STRCHRNUL) && defined(LIBC_BUILD_STRING)
 FAR char *strchrnul(FAR const char *s, int c)
 {
  if (s)
--- a/libs/libc/string/lib_strcmp.c
+++ b/libs/libc/string/lib_strcmp.c
@ -26,11 +26,13 @@

 #include <string.h>

+#include "libc.h"
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/

-#ifndef CONFIG_LIBC_ARCH_STRCMP
+#if !defined(CONFIG_LIBC_ARCH_STRCMP) && defined(LIBC_BUILD_STRING)
 #undef strcmp /* See mm/README.txt */
 int strcmp(FAR const char *cs, FAR const char *ct)
 {
--- a/libs/libc/string/lib_strcpy.c
+++ b/libs/libc/string/lib_strcpy.c
@ -26,6 +26,8 @@

 #include <string.h>

+#include "libc.h"
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/
@ -42,7 +44,7 @@
 *
 ****************************************************************************/

-#ifndef CONFIG_LIBC_ARCH_STRCPY
+#if !defined(CONFIG_LIBC_ARCH_STRCPY) && defined(LIBC_BUILD_STRING)
 #undef strcpy /* See mm/README.txt */
 FAR char *strcpy(FAR char *dest, FAR const char *src)
 {
--- a/libs/libc/string/lib_strlcat.c
+++ b/libs/libc/string/lib_strlcat.c
@ -27,6 +27,8 @@
 #include <sys/types.h>
 #include <string.h>

+#include "libc.h"
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/
@ -44,7 +46,7 @@
 *
 ****************************************************************************/

-#ifndef CONFIG_LIBC_ARCH_STRLCAT
+#if !defined(CONFIG_LIBC_ARCH_STRLCAT) && defined(LIBC_BUILD_STRING)
 size_t strlcat(FAR char *dst, FAR const char *src, size_t dsize)
 {
  FAR const char *odst = dst;
--- a/libs/libc/string/lib_strlcpy.c
+++ b/libs/libc/string/lib_strlcpy.c
@ -27,6 +27,8 @@
 #include <sys/types.h>
 #include <string.h>

+#include "libc.h"
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/
@ -43,7 +45,7 @@
 *
 ****************************************************************************/

-#ifndef CONFIG_LIBC_ARCH_STRLCPY
+#if !defined(CONFIG_LIBC_ARCH_STRLCPY) && defined(LIBC_BUILD_STRING)
 size_t strlcpy(FAR char *dst, FAR const char *src, size_t dsize)
 {
  FAR const char *osrc = src;
--- a/libs/libc/string/lib_strlen.c
+++ b/libs/libc/string/lib_strlen.c
@ -26,11 +26,13 @@
 #include <sys/types.h>
 #include <string.h>

+#include "libc.h"
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/

-#ifndef CONFIG_LIBC_ARCH_STRLEN
+#if !defined(CONFIG_LIBC_ARCH_STRLEN) && defined(LIBC_BUILD_STRING)
 #undef strlen /* See mm/README.txt */
 size_t strlen(const char *s)
 {
--- a/libs/libc/string/lib_strncasecmp.c
+++ b/libs/libc/string/lib_strncasecmp.c
@ -28,11 +28,13 @@
 #include <strings.h>
 #include <ctype.h>

+#include "libc.h"
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/

-#ifndef CONFIG_LIBC_ARCH_STRNCASECMP
+#if !defined(CONFIG_LIBC_ARCH_STRNCASECMP) && defined(LIBC_BUILD_STRING)
 #undef strncasecmp /* See mm/README.txt */
 int strncasecmp(FAR const char *cs, FAR const char *ct, size_t nb)
 {
--- a/libs/libc/string/lib_strncat.c
+++ b/libs/libc/string/lib_strncat.c
@ -26,11 +26,13 @@
 #include <sys/types.h>
 #include <string.h>

+#include "libc.h"
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/

-#ifndef CONFIG_LIBC_ARCH_STRNCAT
+#if !defined(CONFIG_LIBC_ARCH_STRNCAT) && defined(LIBC_BUILD_STRING)
 #undef strncat /* See mm/README.txt */
 FAR char *strncat(FAR char *dest, FAR const char *src, size_t n)
 {
--- a/libs/libc/string/lib_strncmp.c
+++ b/libs/libc/string/lib_strncmp.c
@ -26,11 +26,13 @@
 #include <sys/types.h>
 #include <string.h>

+#include "libc.h"
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/

-#ifndef CONFIG_LIBC_ARCH_STRNCMP
+#if !defined(CONFIG_LIBC_ARCH_STRNCMP) && defined(LIBC_BUILD_STRING)
 #undef strncmp /* See mm/README.txt */
 int strncmp(FAR const char *cs, FAR const char *ct, size_t nb)
 {
--- a/libs/libc/string/lib_strncpy.c
+++ b/libs/libc/string/lib_strncpy.c
@ -26,6 +26,8 @@
 #include <sys/types.h>
 #include <string.h>

+#include "libc.h"
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/
@ -51,7 +53,7 @@
 *
 ****************************************************************************/

-#ifndef CONFIG_LIBC_ARCH_STRNCPY
+#if !defined(CONFIG_LIBC_ARCH_STRNCPY) && defined(LIBC_BUILD_STRING)
 #undef strncpy /* See mm/README.txt */
 FAR char *strncpy(FAR char *dest, FAR const char *src, size_t n)
 {
--- a/libs/libc/string/lib_strnlen.c
+++ b/libs/libc/string/lib_strnlen.c
@ -26,11 +26,13 @@
 #include <sys/types.h>
 #include <string.h>

+#include "libc.h"
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/

-#ifndef CONFIG_LIBC_ARCH_STRNLEN
+#if !defined(CONFIG_LIBC_ARCH_STRNLEN) && defined(LIBC_BUILD_STRING)
 size_t strnlen(const char *s, size_t maxlen)
 {
  const char *sc;
--- a/libs/libc/string/lib_strrchr.c
+++ b/libs/libc/string/lib_strrchr.c
@ -26,6 +26,8 @@

 #include <string.h>

+#include "libc.h"
+
 /****************************************************************************
 * Public Functions
 ****************************************************************************/
@ -34,7 +36,7 @@
 * occurrence of the character c in the string s.
 */

-#ifndef CONFIG_LIBC_ARCH_STRRCHR
+#if !defined(CONFIG_LIBC_ARCH_STRRCHR) && defined(LIBC_BUILD_STRING)
 #undef strrchr /* See mm/README.txt */
 FAR char *strrchr(FAR const char *s, int c)
 {
--- a/libs/libc/string/lib_vikmemcpy.c
+++ b/libs/libc/string/lib_vikmemcpy.c
@ -62,6 +62,10 @@
 #include <stdint.h>
 #include <string.h>

+#include "libc.h"
+
+#if !defined(CONFIG_LIBC_ARCH_MEMCPY) && defined(LIBC_BUILD_STRING)
+
 /****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/
@ -342,3 +346,5 @@ FAR void *memcpy(FAR void *dest, FAR const void *src, size_t count)

  return dest;
 }
+
+#endif