linux/arch
Linus Torvalds ffbc93768e flexible-array member conversion patches for 5.8-rc2
Hi Linus,
 
 Please, pull the following patches that replace zero-length arrays with
 flexible-array members.
 
 Notice that all of these patches have been baking in linux-next for
 two development cycles now.
 
 There is a regular need in the kernel to provide a way to declare having a
 dynamically sized set of trailing elements in a structure. Kernel code should
 always use “flexible array members”[1] for these cases. The older style of
 one-element or zero-length arrays should no longer be used[2].
 
 C99 introduced “flexible array members”, which lacks a numeric size for the
 array declaration entirely:
 
 struct something {
         size_t count;
         struct foo items[];
 };
 
 This is the way the kernel expects dynamically sized trailing elements to be
 declared. It allows the compiler to generate errors when the flexible array
 does not occur last in the structure, which helps to prevent some kind of
 undefined behavior[3] bugs from being inadvertently introduced to the codebase.
 It also allows the compiler to correctly analyze array sizes (via sizeof(),
 CONFIG_FORTIFY_SOURCE, and CONFIG_UBSAN_BOUNDS). For instance, there is no
 mechanism that warns us that the following application of the sizeof() operator
 to a zero-length array always results in zero:
 
 struct something {
         size_t count;
         struct foo items[0];
 };
 
 struct something *instance;
 
 instance = kmalloc(struct_size(instance, items, count), GFP_KERNEL);
 instance->count = count;
 
 size = sizeof(instance->items) * instance->count;
 memcpy(instance->items, source, size);
 
 At the last line of code above, size turns out to be zero, when one might have
 thought it represents the total size in bytes of the dynamic memory recently
 allocated for the trailing array items. Here are a couple examples of this
 issue[4][5]. Instead, flexible array members have incomplete type, and so the
 sizeof() operator may not be applied[6], so any misuse of such operators will
 be immediately noticed at build time.
 
 The cleanest and least error-prone way to implement this is through the use of
 a flexible array member:
 
 struct something {
         size_t count;
         struct foo items[];
 };
 
 struct something *instance;
 
 instance = kmalloc(struct_size(instance, items, count), GFP_KERNEL);
 instance->count = count;
 
 size = sizeof(instance->items[0]) * instance->count;
 memcpy(instance->items, source, size);
 
 Thanks
 --
 Gustavo
 
 [1] https://en.wikipedia.org/wiki/Flexible_array_member
 [2] https://github.com/KSPP/linux/issues/21
 [3] https://git.kernel.org/linus/76497732932f15e7323dc805e8ea8dc11bb587cf
 [4] https://git.kernel.org/linus/f2cd32a443da694ac4e28fbf4ac6f9d5cc63a539
 [5] https://git.kernel.org/linus/ab91c2a89f86be2898cee208d492816ec238b2cf
 [6] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
 -----BEGIN PGP SIGNATURE-----
 
 iQIzBAABCAAdFiEEkmRahXBSurMIg1YvRwW0y0cG2zEFAl7oSmYACgkQRwW0y0cG
 2zGEiw/9FiH3MBwMlPVJPcneY1wCH/N6ZSf+kr7SJiVwV/YbBe9EWuaKZ0D4vAWm
 kTACkOfsZ1me1OKz9wNrOxn0zezTMFQK2PLPgzKIPuK0Hg8MW1EU63RIRsnr0bPc
 b90wZwyBQtLbGRC3/9yAACKwFZe/SeYoV5rr8uylffA35HZW3SZbTex6XnGCF9Q5
 UYwnz7vNg+9VH1GRQeB5jlqL7mAoRzJ49I/TL3zJr04Mn+xC+vVBS7XwipDd03p+
 foC6/KmGhlCO9HMPASReGrOYNPydDAMKLNPdIfUlcTKHWsoTjGOcW/dzfT4rUu6n
 nKr5rIqJ4FdlIvXZL5P5w7Uhkwbd3mus5G0HBk+V/cUScckCpBou+yuGzjxXSitQ
 o0qPsGjWr3v+gxRWHj8YO/9MhKKKW0Iy+QmAC9+uLnbfJdbUwYbLIXbsOKnokCA8
 jkDEr64F5hFTKtajIK4VToJK1CsM3D9dwTub27lwZysHn3RYSQdcyN+9OiZgdzpc
 GlI6QoaqKR9AT4b/eBmqlQAKgA07zSQ5RsIjRm6hN3d7u/77x2kyrreo+trJyVY2
 F17uEOzfTqZyxtkPayE8DVjTtbByoCuBR0Vm1oMAFxjyqZQY5daalB0DKd1mdYqi
 khIXqNAuYqHOb898fEuzidjV38hxZ9y8SAym3P7WnYl+Hxz+8Jo=
 =8HUQ
 -----END PGP SIGNATURE-----

Merge tag 'flex-array-conversions-5.8-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux

Pull flexible-array member conversions from Gustavo A. R. Silva:
 "Replace zero-length arrays with flexible-array members.

  Notice that all of these patches have been baking in linux-next for
  two development cycles now.

  There is a regular need in the kernel to provide a way to declare
  having a dynamically sized set of trailing elements in a structure.
  Kernel code should always use “flexible array members”[1] for these
  cases. The older style of one-element or zero-length arrays should no
  longer be used[2].

  C99 introduced “flexible array members”, which lacks a numeric size
  for the array declaration entirely:

        struct something {
                size_t count;
                struct foo items[];
        };

  This is the way the kernel expects dynamically sized trailing elements
  to be declared. It allows the compiler to generate errors when the
  flexible array does not occur last in the structure, which helps to
  prevent some kind of undefined behavior[3] bugs from being
  inadvertently introduced to the codebase.

  It also allows the compiler to correctly analyze array sizes (via
  sizeof(), CONFIG_FORTIFY_SOURCE, and CONFIG_UBSAN_BOUNDS). For
  instance, there is no mechanism that warns us that the following
  application of the sizeof() operator to a zero-length array always
  results in zero:

        struct something {
                size_t count;
                struct foo items[0];
        };

        struct something *instance;

        instance = kmalloc(struct_size(instance, items, count), GFP_KERNEL);
        instance->count = count;

        size = sizeof(instance->items) * instance->count;
        memcpy(instance->items, source, size);

  At the last line of code above, size turns out to be zero, when one
  might have thought it represents the total size in bytes of the
  dynamic memory recently allocated for the trailing array items. Here
  are a couple examples of this issue[4][5].

  Instead, flexible array members have incomplete type, and so the
  sizeof() operator may not be applied[6], so any misuse of such
  operators will be immediately noticed at build time.

  The cleanest and least error-prone way to implement this is through
  the use of a flexible array member:

        struct something {
                size_t count;
                struct foo items[];
        };

        struct something *instance;

        instance = kmalloc(struct_size(instance, items, count), GFP_KERNEL);
        instance->count = count;

        size = sizeof(instance->items[0]) * instance->count;
        memcpy(instance->items, source, size);

  instead"

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")
[4] commit f2cd32a443 ("rndis_wlan: Remove logically dead code")
[5] commit ab91c2a89f ("tpm: eventlog: Replace zero-length array with flexible-array member")
[6] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html

* tag 'flex-array-conversions-5.8-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux: (41 commits)
  w1: Replace zero-length array with flexible-array
  tracing/probe: Replace zero-length array with flexible-array
  soc: ti: Replace zero-length array with flexible-array
  tifm: Replace zero-length array with flexible-array
  dmaengine: tegra-apb: Replace zero-length array with flexible-array
  stm class: Replace zero-length array with flexible-array
  Squashfs: Replace zero-length array with flexible-array
  ASoC: SOF: Replace zero-length array with flexible-array
  ima: Replace zero-length array with flexible-array
  sctp: Replace zero-length array with flexible-array
  phy: samsung: Replace zero-length array with flexible-array
  RxRPC: Replace zero-length array with flexible-array
  rapidio: Replace zero-length array with flexible-array
  media: pwc: Replace zero-length array with flexible-array
  firmware: pcdp: Replace zero-length array with flexible-array
  oprofile: Replace zero-length array with flexible-array
  block: Replace zero-length array with flexible-array
  tools/testing/nvdimm: Replace zero-length array with flexible-array
  libata: Replace zero-length array with flexible-array
  kprobes: Replace zero-length array with flexible-array
  ...
2020-06-16 17:23:57 -07:00
..
alpha Kbuild updates for v5.8 (2nd) 2020-06-13 13:29:16 -07:00
arc treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
arm Kbuild updates for v5.8 (2nd) 2020-06-13 13:29:16 -07:00
arm64 Kbuild updates for v5.8 (2nd) 2020-06-13 13:29:16 -07:00
c6x This time around we have 4 lines of diff in the core framework, removing a 2020-06-10 11:42:19 -07:00
csky mmap locking API: use coccinelle to convert mmap_sem rwsem call sites 2020-06-09 09:39:14 -07:00
h8300 This time around we have 4 lines of diff in the core framework, removing a 2020-06-10 11:42:19 -07:00
hexagon treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
ia64 ia64: kernel: unwind_i.h: Replace zero-length array with flexible-array 2020-06-15 23:08:31 -05:00
m68k Kbuild updates for v5.8 (2nd) 2020-06-13 13:29:16 -07:00
microblaze mmap locking API: convert mmap_sem comments 2020-06-09 09:39:14 -07:00
mips Kbuild updates for v5.8 (2nd) 2020-06-13 13:29:16 -07:00
nds32 mmap locking API: convert mmap_sem comments 2020-06-09 09:39:14 -07:00
nios2 nios2 update for v5.8-rc1 2020-06-12 11:55:11 -07:00
openrisc OpenRISC updates for 5.8 2020-06-13 10:54:09 -07:00
parisc treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
powerpc Kbuild updates for v5.8 (2nd) 2020-06-13 13:29:16 -07:00
riscv RISC-V Patches for the 5.8 Merge Window, Part 2 2020-06-11 12:55:20 -07:00
s390 Kbuild updates for v5.8 (2nd) 2020-06-13 13:29:16 -07:00
sh treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
sparc treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
um treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00
unicore32 This time around we have 4 lines of diff in the core framework, removing a 2020-06-10 11:42:19 -07:00
x86 x86/purgatory: Add -fno-stack-protector 2020-06-16 17:05:07 -07:00
xtensa mmap locking API: convert mmap_sem API comments 2020-06-09 09:39:14 -07:00
.gitignore
Kconfig treewide: replace '---help---' in Kconfig files with 'help' 2020-06-14 01:57:21 +09:00