The practice of using __pure getter functions to access global
variables in the EFI stub dates back to the time when we had to
carefully prevent GOT entries from being emitted, because we
could not rely on the toolchain to do this for us.
Today, we use the hidden visibility pragma for all EFI stub source
files, which now all live in the same subdirectory, and we apply a
sanity check on the objects, so we can get rid of these getter
functions and simply refer to global data objects directly.
Start with efi_system_table(), and convert it into a global variable.
While at it, make it a pointer-to-const, because we can.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Instead of using __efistub_global to force variables into the .data
section, leave them in the .bss but pull the EFI stub's .bss section
into .data in the linker script for the compressed kernel.
Add relocation checking for x86 as well to catch non-PC-relative
relocations that require runtime processing, since the EFI stub does not
do any runtime relocation processing.
This will catch, for example, data relocations created by static
initializers of pointers.
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200416151227.3360778-3-nivedita@alum.mit.edu
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Move efi_relocate_kernel() into a separate source file, so that it
only gets pulled into builds for architectures that use it. Since
efi_relocate_kernel() is the only user of efi_low_alloc(), let's
move that over as well.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
It is no longer necessary to locate the kernel as low as possible in
physical memory, and so we can switch from efi_low_alloc() [which is
a rather nasty concoction on top of GetMemoryMap()] to a new helper
called efi_allocate_pages_aligned(), which simply rounds up the size
to account for the alignment, and frees the misaligned pages again.
So considering that the kernel can live anywhere in the physical
address space, as long as its alignment requirements are met, let's
switch to efi_allocate_pages_aligned() to allocate the pages.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Break out the code to create an aligned page allocation from mem.c
and move it into a function efi_allocate_pages_aligned() in alignedmem.c.
Update efi_allocate_pages() to invoke it unless the minimum alignment
equals the EFI page size (4 KB), in which case the ordinary page
allocator is sufficient. This way, efi_allocate_pages_aligned() will
only be pulled into the build if it is actually being used (which will
be on arm64 only in the immediate future)
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
The KASLR code path in the arm64 version of the EFI stub incorporates
some overly complicated logic to randomly allocate a region of the right
alignment: there is no need to randomize the placement of the kernel
modulo 2 MiB separately from the placement of the 2 MiB aligned allocation
itself - we can simply follow the same logic used by the non-randomized
placement, which is to allocate at the correct alignment, and only take
TEXT_OFFSET into account if it is not a round multiple of the alignment.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
The notion of a 'preferred' load offset for the kernel dates back to the
times when the kernel's primary mapping overlapped with the linear region,
and memory below it could not be used at all.
Today, the arm64 kernel does not really care where it is loaded in physical
memory, as long as the alignment requirements are met, and so there is no
point in unconditionally moving the kernel to a new location in memory at
boot. Instead, we can
- check for a KASLR seed, and randomly reallocate the kernel if one is
provided
- otherwise, check whether the alignment requirements are met for the
current placement of the kernel, and just run it in place if they are
- finally, do an ordinary page allocation and reallocate the kernel to a
suitably aligned buffer anywhere in memory.
By the same reasoning, there is no need to take TEXT_OFFSET into account
if it is a round multiple of the minimum alignment, which is the usual
case for relocatable kernels with TEXT_OFFSET randomization disabled.
Otherwise, it suffices to use the relative misaligment of TEXT_OFFSET
when reallocating the kernel.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
The implementation of efi_random_alloc() arbitrarily truncates the
provided random seed to 16 bits, which limits the granularity of the
randomly chosen allocation offset in memory. This is currently only
an issue if the size of physical memory exceeds 128 GB, but going
forward, we will reduce the allocation alignment to 64 KB, and this
means we need to increase the granularity to ensure that the random
memory allocations are distributed evenly.
We will need to switch to 64-bit arithmetic for the multiplication,
but this does not result in 64-bit integer intrinsic calls on ARM or
on i386.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
The EFI stub uses a per-architecture #define for the minimum base
and size alignment of page allocations, which is set to 4 KB for
all architecures except arm64, which uses 64 KB, to ensure that
allocations can always be (un)mapped efficiently, regardless of
the page size used by the kernel proper, which could be a kexec'ee
The API wrappers around page based allocations assume that this
alignment is always taken into account, and so efi_free() will
also round up its size argument to EFI_ALLOC_ALIGN.
Currently, efi_random_alloc() does not honour this alignment for
the allocated size, and so freeing such an allocation may result
in unrelated memory to be freed, potentially leading to issues
after boot. So let's round up size in efi_random_alloc() as well.
Fixes: 2ddbfc81ea ("efi: stub: add implementation of efi_random_alloc()")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Add the ability to automatically pick the highest resolution video mode
(defined as the product of vertical and horizontal resolution) by using
a command-line argument of the form
video=efifb:auto
If there are multiple modes with the highest resolution, pick one with
the highest color depth.
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200328160601.378299-2-nivedita@alum.mit.edu
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
pixel_format must be one of
PIXEL_RGB_RESERVED_8BIT_PER_COLOR
PIXEL_BGR_RESERVED_8BIT_PER_COLOR
PIXEL_BIT_MASK
since we skip PIXEL_BLT_ONLY when finding a gop.
Remove the redundant code and add another check in find_gop to skip any
pixel formats that we don't know about, in case a later version of the
UEFI spec adds one.
Reformat the code a little.
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200320020028.1936003-10-nivedita@alum.mit.edu
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
We have wrappers around EFI calls so that x86 can define special
versions for mixed mode, while all other architectures can use the
same simple definition that just issues the call directly.
In preparation for the arrival of yet another architecture that doesn't
need anything special here (RISC-V), let's move the default definition
into a shared header.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Loading an initrd passed via the kernel command line is deprecated: it
is limited to files that reside in the same volume as the one the kernel
itself was loaded from, and we have more flexible ways to achieve the
same. So make it configurable so new architectures can decide not to
enable it.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
When remapping a mapping where a portion of a VMA is remapped
into another portion of the VMA it can cause the VMA to become
split. During the copy_vma operation the VMA can actually
be remerged if it's an anonymous VMA whose pages have not yet
been faulted. This isn't normally a problem because at the end
of the remap the original portion is unmapped causing it to
become split again.
However, MREMAP_DONTUNMAP leaves that original portion in place which
means that the VMA which was split and then remerged is not actually
split at the end of the mremap. This patch fixes a bug where
we don't detect that the VMAs got remerged and we end up
putting back VM_ACCOUNT on the next mapping which is completely
unreleated. When that next mapping is unmapped it results in
incorrectly unaccounting for the memory which was never accounted,
and eventually we will underflow on the memory comittment.
There is also another issue which is similar, we're currently
accouting for the number of pages in the new_vma but that's wrong.
We need to account for the length of the remap operation as that's
all that is being added. If there was a mapping already at that
location its comittment would have been adjusted as part of
the munmap at the start of the mremap.
A really simple repro can be seen in:
https://gist.github.com/bgaff/e101ce99da7d9a8c60acc641d07f312c
Fixes: e346b38130 ("mm/mremap: add MREMAP_DONTUNMAP to mremap()")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Brian Geffon <bgeffon@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Pull clk fixes from Stephen Boyd:
"Two build fixes for a couple clk drivers and a fix for the Unisoc
serial clk where we want to keep it on for earlycon"
* tag 'clk-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/clk/linux:
clk: sprd: don't gate uart console clock
clk: mmp2: fix link error without mmp2
clk: asm9260: fix __clk_hw_register_fixed_rate_with_accuracy typo
Pull x86 and objtool fixes from Thomas Gleixner:
"A set of fixes for x86 and objtool:
objtool:
- Ignore the double UD2 which is emitted in BUG() when
CONFIG_UBSAN_TRAP is enabled.
- Support clang non-section symbols in objtool ORC dump
- Fix switch table detection in .text.unlikely
- Make the BP scratch register warning more robust.
x86:
- Increase microcode maximum patch size for AMD to cope with new CPUs
which have a larger patch size.
- Fix a crash in the resource control filesystem when the removal of
the default resource group is attempted.
- Preserve Code and Data Prioritization enabled state accross CPU
hotplug.
- Update split lock cpu matching to use the new X86_MATCH macros.
- Change the split lock enumeration as Intel finaly decided that the
IA32_CORE_CAPABILITIES bits are not architectural contrary to what
the SDM claims. !@#%$^!
- Add Tremont CPU models to the split lock detection cpu match.
- Add a missing static attribute to make sparse happy"
* tag 'x86-urgent-2020-04-19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/split_lock: Add Tremont family CPU models
x86/split_lock: Bits in IA32_CORE_CAPABILITIES are not architectural
x86/resctrl: Preserve CDP enable over CPU hotplug
x86/resctrl: Fix invalid attempt at removing the default resource group
x86/split_lock: Update to use X86_MATCH_INTEL_FAM6_MODEL()
x86/umip: Make umip_insns static
x86/microcode/AMD: Increase microcode PATCH_MAX_SIZE
objtool: Make BP scratch register warning more robust
objtool: Fix switch table detection in .text.unlikely
objtool: Support Clang non-section symbols in ORC generation
objtool: Support Clang non-section symbols in ORC dump
objtool: Fix CONFIG_UBSAN_TRAP unreachable warnings
Pull time namespace fix from Thomas Gleixner:
"An update for the proc interface of time namespaces: Use symbolic
names instead of clockid numbers. The usability nuisance of numbers
was noticed by Michael when polishing the man page"
* tag 'timers-urgent-2020-04-19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
proc, time/namespace: Show clock symbolic names in /proc/pid/timens_offsets
Pull perf tooling fixes and updates from Thomas Gleixner:
- Fix the header line of perf stat output for '--metric-only --per-socket'
- Fix the python build with clang
- The usual tools UAPI header synchronization
* tag 'perf-urgent-2020-04-19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
tools headers: Synchronize linux/bits.h with the kernel sources
tools headers: Adopt verbatim copy of compiletime_assert() from kernel sources
tools headers: Update x86's syscall_64.tbl with the kernel sources
tools headers UAPI: Sync drm/i915_drm.h with the kernel sources
tools headers UAPI: Update tools's copy of drm.h headers
tools headers kvm: Sync linux/kvm.h with the kernel sources
tools headers UAPI: Sync linux/fscrypt.h with the kernel sources
tools include UAPI: Sync linux/vhost.h with the kernel sources
tools arch x86: Sync asm/cpufeatures.h with the kernel sources
tools headers UAPI: Sync linux/mman.h with the kernel
tools headers UAPI: Sync sched.h with the kernel
tools headers: Update linux/vdso.h and grab a copy of vdso/const.h
perf stat: Fix no metric header if --per-socket and --metric-only set
perf python: Check if clang supports -fno-semantic-interposition
tools arch x86: Sync the msr-index.h copy with the kernel sources
Pull irq fixes from Thomas Gleixner:
"A set of fixes/updates for the interrupt subsystem:
- Remove setup_irq() and remove_irq(). All users have been converted
so remove them before new users surface.
- A set of bugfixes for various interrupt chip drivers
- Add a few missing static attributes to address sparse warnings"
* tag 'irq-urgent-2020-04-19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
irqchip/irq-bcm7038-l1: Make bcm7038_l1_of_init() static
irqchip/irq-mvebu-icu: Make legacy_bindings static
irqchip/meson-gpio: Fix HARDIRQ-safe -> HARDIRQ-unsafe lock order
irqchip/sifive-plic: Fix maximum priority threshold value
irqchip/ti-sci-inta: Fix processing of masked irqs
irqchip/mbigen: Free msi_desc on device teardown
irqchip/gic-v4.1: Update effective affinity of virtual SGIs
irqchip/gic-v4.1: Add support for VPENDBASER's Dirty+Valid signaling
genirq: Remove setup_irq() and remove_irq()
Pull scheduler fixes from Thomas Gleixner:
"Two fixes for the scheduler:
- Work around an uninitialized variable warning where GCC can't
figure it out.
- Allow 'isolcpus=' to skip unknown subparameters so that older
kernels work with the commandline of a newer kernel. Improve the
error output while at it"
* tag 'sched-urgent-2020-04-19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
sched/vtime: Work around an unitialized variable warning
sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters
Pull RCU fix from Thomas Gleixner:
"A single bugfix for RCU to prevent taking a lock in NMI context"
* tag 'core-urgent-2020-04-19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
rcu: Don't acquire lock in NMI handler in rcu_nmi_enter_common()
Pull ext4 fixes from Ted Ts'o:
"Miscellaneous bug fixes and cleanups for ext4, including a fix for
generic/388 in data=journal mode, removing some BUG_ON's, and cleaning
up some compiler warnings"
* tag 'ext4_for_linus_stable' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4:
ext4: convert BUG_ON's to WARN_ON's in mballoc.c
ext4: increase wait time needed before reuse of deleted inode numbers
ext4: remove set but not used variable 'es' in ext4_jbd2.c
ext4: remove set but not used variable 'es'
ext4: do not zeroout extents beyond i_disksize
ext4: fix return-value types in several function comments
ext4: use non-movable memory for superblock readahead
ext4: use matching invalidatepage in ext4_writepage
Pull cifs fixes from Steve French:
"Three small smb3 fixes: two debug related (helping network tracing for
SMB2 mounts, and the other removing an unintended debug line on
signing failures), and one fixing a performance problem with 64K
pages"
* tag '5.7-rc-smb3-fixes' of git://git.samba.org/sfrench/cifs-2.6:
smb3: remove overly noisy debug line in signing errors
cifs: improve read performance for page size 64KB & cache=strict & vers=2.1+
cifs: dump the session id and keys also for SMB2 sessions
Pull flexible-array member conversion from Gustavo Silva:
"The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array
member[1][2], introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof
operator may not be applied. As a quirk of the original
implementation of zero-length arrays, sizeof evaluates to zero."[1]
sizeof(flexible-array-member) triggers a warning because flexible
array members have incomplete type[1]. There are some instances of
code in which the sizeof operator is being incorrectly/erroneously
applied to zero-length arrays and the result is zero. Such instances
may be hiding some bugs. So, this work (flexible-array member
convertions) will also help to get completely rid of those sorts of
issues.
Notice that all of these patches have been baking in linux-next for
quite a while now and, 238 more of these patches have already been
merged into 5.7-rc1.
There are a couple hundred more of these issues waiting to be
addressed in the whole codebase"
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")
* tag 'flexible-array-member-5.7-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux: (28 commits)
xattr.h: Replace zero-length array with flexible-array member
uapi: linux: fiemap.h: Replace zero-length array with flexible-array member
uapi: linux: dlm_device.h: Replace zero-length array with flexible-array member
tpm_eventlog.h: Replace zero-length array with flexible-array member
ti_wilink_st.h: Replace zero-length array with flexible-array member
swap.h: Replace zero-length array with flexible-array member
skbuff.h: Replace zero-length array with flexible-array member
sched: topology.h: Replace zero-length array with flexible-array member
rslib.h: Replace zero-length array with flexible-array member
rio.h: Replace zero-length array with flexible-array member
posix_acl.h: Replace zero-length array with flexible-array member
platform_data: wilco-ec.h: Replace zero-length array with flexible-array member
memcontrol.h: Replace zero-length array with flexible-array member
list_lru.h: Replace zero-length array with flexible-array member
lib: cpu_rmap: Replace zero-length array with flexible-array member
irq.h: Replace zero-length array with flexible-array member
ihex.h: Replace zero-length array with flexible-array member
igmp.h: Replace zero-length array with flexible-array member
genalloc.h: Replace zero-length array with flexible-array member
ethtool.h: Replace zero-length array with flexible-array member
...
Pull SCSI fixes from James Bottomley:
"Seven fixes: three in target, one on a sg error leg, two in qla2xxx
fixing warnings introduced in the last merge window and updating
MAINTAINERS and one in hisi_sas fixing a problem introduced by libata"
* tag 'scsi-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi:
scsi: sg: add sg_remove_request in sg_common_write
scsi: target: tcmu: reset_ring should reset TCMU_DEV_BIT_BROKEN
scsi: target: fix PR IN / READ FULL STATUS for FC
scsi: target: Write NULL to *port_nexus_ptr if no ISID
scsi: MAINTAINERS: Update qla2xxx FC-SCSI driver maintainer
scsi: qla2xxx: Fix regression warnings
scsi: hisi_sas: Fix build error without SATA_HOST
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
This issue was found with the help of Coccinelle.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
This issue was found with the help of Coccinelle.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
This issue was found with the help of Coccinelle.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
This issue was found with the help of Coccinelle.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
This issue was found with the help of Coccinelle.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
This issue was found with the help of Coccinelle.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
This issue was found with the help of Coccinelle.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
This issue was found with the help of Coccinelle.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
