From mboxrd@z Thu Jan 1 00:00:00 1970 From: Simon Glass Date: Thu, 6 May 2021 10:41:40 -0700 Subject: [PATCH v2 01/50] lib: Add memdup() In-Reply-To: <20210506170739.4tz7yumpfp2kfli4@ti.com> References: <20210506142438.1310977-1-sjg@chromium.org> <20210506082420.v2.1.I1d417387eb1e7273b536017f4a8920fc4e2369a9@changeid> <20210506170739.4tz7yumpfp2kfli4@ti.com> Message-ID: List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: u-boot@lists.denx.de Hi Pratyush, On Thu, 6 May 2021 at 10:07, Pratyush Yadav wrote: > > 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 > > --- > > > > 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? I think it is just a 0-length pointer and that the only thing you can do with it is call free(). I am certainly no expert on this sort of thing though. It seems that some implementations return NULL for a zero size, some return a valid pointer which can be passed to free(). Of course, U-Boot lets you pass NULL to free() anyway. Regards, Simon