RE: [PATCH v2] eal: add nonnull and access function attributes

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Morten Brørup [mailto:mb@smartsharesystems.com]
> Sent: Saturday, 3 December 2022 15.23
> 
> Add "nonnull" function attribute to help the compiler detect a NULL
> pointer being passed to a function not accepting NULL pointers as an
> argument at build time.
> 
> Add "access" function attribute to tell the compiler how a function
> accesses its pointer arguments.
> 
> Add these attributes to the rte_memcpy() function, as the first in
> hopefully many to come.

Notes about Warnings/Errors reported in Patchwork [1]:

* The checkpatch warning is about the attributes being defined. This is the purpose of the patch, and I don't know how to do it without getting a checkpatch warning.

* The errors are previously uncaught bugs elsewhere, now being caught by GCC versions >= 10.4.0 due to these new attributes. I have reported these as [Bug 1146]. It shows some actual usefulness of the attributes in this patch, and provides a good example of why we should decorate many more functions with them.

[1]: https://patchwork.dpdk.org/project/dpdk/patch/20221203142244.17135-1-mb@smartsharesystems.com/
[Bug 1146]: https://bugs.dpdk.org/show_bug.cgi?id=1146


Example of previously uncaught bug:

../drivers/net/bnx2x/bnx2x_vfpf.c: In function ‘bnx2x_check_bull’:
../drivers/net/bnx2x/bnx2x_vfpf.c:57:17: error: ‘rte_memcpy’ writing 4 bytes into a region of size 2 overflows the destination [-Werror=stringop-overflow=]
   57 |                 rte_memcpy(&bull->vlan, &sc->old_bulletin.vlan, RTE_VLAN_HLEN);
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from ../drivers/net/bnx2x/bnx2x.h:29,
                 from ../drivers/net/bnx2x/bnx2x_vfpf.c:8:
../drivers/net/bnx2x/bnx2x_vfpf.h:297:18: note: destination object ‘vlan’ of size 2
  297 |         uint16_t vlan;
      |                  ^~~~
../drivers/net/bnx2x/bnx2x_vfpf.c:57:17: error: ‘rte_memcpy’ reading 4 bytes from a region of size 2 [-Werror=stringop-overread]
   57 |                 rte_memcpy(&bull->vlan, &sc->old_bulletin.vlan, RTE_VLAN_HLEN);
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../drivers/net/bnx2x/bnx2x_vfpf.h:297:18: note: source object ‘vlan’ of size 2
  297 |         uint16_t vlan;
      |                  ^~~~
In file included from ../lib/mempool/rte_mempool.h:48,
                 from ../lib/mbuf/rte_mbuf.h:38,
                 from ../lib/net/rte_ether.h:22,
                 from ../lib/ethdev/rte_eth_ctrl.h:10,
                 from ../lib/ethdev/rte_ethdev.h:1419,
                 from ../lib/ethdev/ethdev_driver.h:24,
                 from ../drivers/net/bnx2x/bnx2x_ethdev.h:34,
                 from ../drivers/net/bnx2x/bnx2x.h:23:
../lib/eal/x86/include/rte_memcpy.h:869:1: note: in a call to function ‘rte_memcpy’ declared with attribute ‘access (read_only, 2, 3)’
  869 | rte_memcpy(void *dst, const void *src, size_t n)
      | ^~~~~~~~~~