string: add strdup_const and kstrdup_const

Extend Linux compat by adding kstrdup_const(), backed by lib/string.c.
This leverages U-Boots .rodata section on ARM64 to avoid pointlessly
duplicating const strings.

This is used by the Linux CCF_FULL port and may be useful elsewhere
in U-Boot.

Signed-off-by: Casey Connolly <[email protected]>

2 files changed, 15 insertions, 0 deletions

diff --git a/include/linux/compat.h b/include/linux/compat.h
index 62381451617..d4ba4d0088a 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -67,6 +67,19 @@ static inline void vfree(const void *addr)
 	free((void *)addr);
 }
 
+/**
+ * kstrdup_const - conditionally duplicate an existing const string
+ * @s: the string to duplicate
+ * @gfp: the GFP mask used in the kmalloc() call when allocating memory
+ *
+ * Note: Strings allocated by kstrdup_const should be freed by kfree_const and
+ * must not be passed to krealloc().
+ *
+ * Return: source string if it is in .rodata section otherwise
+ * fallback to kstrdup.
+ */
+#define kstrdup_const(s, gfp) strdup_const(s)
+
 struct kmem_cache { int sz; };
 
 struct kmem_cache *get_mem(int element_sz);
diff --git a/include/linux/string.h b/include/linux/string.h
index d943fcce690..a8a6cf4af50 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -104,6 +104,8 @@ size_t strcspn(const char *s, const char *reject);
 #ifndef __HAVE_ARCH_STRDUP
 extern char * strdup(const char *);
 extern char * strndup(const char *, size_t);
+extern const char *strdup_const(const char *s);
+extern void kfree_const(const void *x);
 #endif
 #ifndef __HAVE_ARCH_STRSWAB
 extern char * strswab(const char *);