[PATCH v2 01/50] lib: Add memdup()

[Pratyush Yadav]

On 06/05/21 08:23AM, Simon Glass wrote:
> Add a function to duplicate a memory region, a little like strdup().
> 
> Signed-off-by: Simon Glass <sjg at chromium.org>
> ---
> 
> Changes in v2:
> - Add a patch to introduce a memdup() function
> 
>  include/linux/string.h | 13 +++++++++++++
>  lib/string.c           | 13 +++++++++++++
>  test/lib/string.c      | 32 ++++++++++++++++++++++++++++++++
>  3 files changed, 58 insertions(+)
> 
> diff --git a/include/linux/string.h b/include/linux/string.h
> index dd255f21633..3169c93796e 100644
> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> @@ -129,6 +129,19 @@ extern void * memchr(const void *,int,__kernel_size_t);
>  void *memchr_inv(const void *, int, size_t);
>  #endif
>  
> +/**
> + * memdup() - allocate a buffer and copy in the contents
> + *
> + * Note that this returns a valid pointer even if @len is 0

I'm uneducated about U-Boot's memory allocator. But I wonder how it 
returns a valid pointer even on 0 length allocations. What location does 
it point to? What are users expected to do with that pointer? They 
obviously can't read/write to it since it is supposed to be a 0 byte 
long allocation. If another positive length allocation happens before 
the said pointer is freed, will it point to the same memory location? If 
not, isn't the 0-length pointer actually at least a 1-length pointer?

> + *
> + * @src: data to copy in
> + * @len: number of bytes to copy
> + * @return allocated buffer with the copied contents, or NULL if not enough
> + *	memory is available
> + *
> + */
> +char *memdup(const void *src, size_t len);
> +
>  unsigned long ustrtoul(const char *cp, char **endp, unsigned int base);
>  unsigned long long ustrtoull(const char *cp, char **endp, unsigned int base);
>  
> diff --git a/lib/string.c b/lib/string.c
> index a0cff8fe88e..1be61ee0499 100644
> --- a/lib/string.c
> +++ b/lib/string.c
> @@ -658,6 +658,19 @@ void * memscan(void * addr, int c, size_t size)
>  }
>  #endif
>  
> +char *memdup(const void *src, size_t len)
> +{
> +	char *p;
> +
> +	p = malloc(len);
> +	if (!p)
> +		return NULL;
> +
> +	memcpy(p, src, len);
> +
> +	return p;
> +}
> +
>  #ifndef __HAVE_ARCH_STRSTR
>  /**
>   * strstr - Find the first substring in a %NUL terminated string
[...]

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.