The ALIGNMENT error was missing a string, leading to <unknown error>
being returned.
Signed-off-by: Georg Kotheimer <georg.kotheimer@kernkonzept.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
With -Wsign-compare, compilers warn about a mismatching signedness in
the different legs of the conditional operator, in fdtget.c.
In the questionable expression, we are constructing a 16-bit value out of
two unsigned 8-bit values, however are relying on the compiler's
automatic expansion of the uint8_t to a larger type, to survive the left
shift. This larger type happens to be an "int", so this part of the
expression becomes signed.
Fix this by explicitly blowing up the uint8_t to a larger *unsigned* type,
before doing the left shift. And while we are at it, convert the hardly
readable conditional operator usage into a sane switch/case expression.
This fixes "make fdtget", when compiled with -Wsign-compare.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Message-Id: <20210618172030.9684-3-andre.przywara@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Coverity gets a bit confused by loading fdt_size_dt_strings() and
using it in a memmove(). In fact this is safe because the callers
have verified this information (via FDT_RW_PROBE() in fdt_pack() or
construction in fdt_open_into()).
Passing in strings_size like we already do struct_size seems to get
Coverity to follow what's going on here.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Only checking the FDT alignment in fdt_ro_probe_() means that
fdt_check_header() can pass, but then subsequent API calls fail on
alignment checks. Let's add an alignment check to fdt_check_header() so
alignment errors are found up front.
Cc: Tom Rini <trini@konsulko.com>
Cc: Frank Rowand <frowand.list@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Message-Id: <20210406190712.2118098-1-robh@kernel.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
The root node is supposed to have an empty name, but at present this is
not checked. The behaviour of such a tree is not well defined. Most
software rightly assumes that the root node is at offset 0 and does not
check the name. This oddity was discovered as part of a security
investigation into U-Boot verified boot.
Add a check for this to fdt_check_full().
Signed-off-by: Simon Glass <sjg@chromium.org>
Reported-by: Arie Haenel <arie.haenel@intel.com>
Reported-by: Julien Lenoir <julien.lenoir@intel.com>
Message-Id: <20210323010410.3222701-2-sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
At present it is possible to have two root nodes and even access nodes
in the 'second' root. Such trees should not be considered valid. This
was discovered as part of a security investigation into U-Boot verified
boot.
Add a check for this to fdt_check_full().
Signed-off-by: Simon Glass <sjg@chromium.org>
Reported-by: Arie Haenel <arie.haenel@intel.com>
Reported-by: Julien Lenoir <julien.lenoir@intel.com>
Message-Id: <20210323000926.3210733-1-sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Apparently the unchecked return value of the first fdt_next_tag() call in
fdt_add_subnode_namelen() is tripping Coverity Scan in some circumstances,
although it appears not to for the scan on our project itself.
This fdt_next_tag() should always return FDT_BEGIN_NODE, since otherwise
the fdt_subnode_offset_namelen() above would have returned BADOFFSET or
BADSTRUCTURE.
Still, add a check to shut Coverity up, gated by a can_assume() to avoid
bloat in small builds.
Reported-by: Ryan Long <ryan.long@oarcorp.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Changes in v3:
- Remove noop version sets
- Set version correctly on loaded fdt in fdt_open_into
Fixes: f1879e1a50 ("Add limited read-only support for older (V2 and V3) device tree to libfdt.")
Signed-off-by: Justin Covell <jujugoboom@gmail.com>
Message-Id: <20201229041749.2187-1-jujugoboom@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
There's a small inaccuracy in the comment describing these new helpers.
This corrects it, and reformats while we're there.
Fixes: f98f28ab ("libfdt: Internally perform potentially unaligned loads")
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Commits 6dcb8ba4 "libfdt: Add helpers for accessing unaligned words"
introduced changes to support unaligned reads for ARM platforms and
11738cf01f "libfdt: Don't use memcpy to handle unaligned reads on ARM"
improved the performance of these helpers.
On further discussion, while there are potential cases where we could be
used on platforms that do not fixup unaligned reads for us, making this
choice the default is very expensive in terms of binary size and access
time. To address this, introduce and use new fdt{32,64}_ld_ functions
that call fdt{32,64}_to_cpu() as was done prior to the above mentioned
commits. Leave the existing load functions as unaligned-safe and
include comments in both cases.
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Tom Rini <trini@konsulko.com>
Message-Id: <20201211022736.31657-1-trini@konsulko.com>
Tested-by: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
The device tree must be loaded in to memory at an 8-byte aligned
address. Add a check for this condition in fdt_ro_probe_() and a new
error code to return if we are not.
Signed-off-by: Tom Rini <trini@konsulko.com>
Message-Id: <20201104130605.28874-1-trini@konsulko.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
The meson build system allows projects to "vendor" dtc easily, thanks to
subproject(). QEMU has recently switched to meson, and adding meson
support to dtc will help to handle the QEMU submodule.
meson rules are arguably simpler to write and maintain than
the hand-crafted/custom Makefile. meson support various backends, and
default build options (including coverage, sanitizer, debug/release
etc, see: https://mesonbuild.com/Builtin-options.html)
Compare to the Makefiles, the same build targets should be built and
installed and the same tests should be run ("meson test" can be provided
extra test arguments for running the equivalent of checkm/checkv).
There is no support EXTRAVERSION/LOCAL_VERSION/CONFIG_LOCALVERSION,
instead the version is simply set with project(), and vcs_tag() is
used for git/dirty version reporting (This is most common and is
hopefully enough. If necessary, configure-time options could be added
for extra versioning.).
libfdt shared library is build following regular naming conventions:
instead of libfdt.so.1 -> libfdt-1.6.0.so (with current build-sys),
libfdt.so.1 -> libfdt.so.1.6.0. I am not sure why the current build
system use an uncommon naming pattern. I also included a libfdt.pc
pkg-config file, as convenience.
Both Linux native build and mingw cross-build pass. CI pass. Tests are
only run on native build.
The current Makefiles are left in-tree, and make/check still work.
Eventually, the Makefiles could be marked as deprecated, to start a
transition period and avoid having to maintain 2 build systems in the
near future.
(run_tests.sh could eventually be replaced by the meson test runner,
which would have several advantages in term of flexibility/features,
but this is left for another day)
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20201012073405.1682782-3-marcandre.lureau@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
The API documentation in libfdt.h seems to follow the Linux kernel's
kernel-doc format[1].
Running "scripts/kernel-doc -v -none" on the file reports some problems,
mostly missing return values and missing parameter descriptions.
Fix those up by providing the missing bits, and fixing the other small
issues reported by the script.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/doc-guide/kernel-doc.rst
Message-Id: <20201012165331.25016-1-andre.przywara@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
With -Wsign-compare, compilers warn about a mismatching signedness
in a comparison in fdt_strerror().
Force FDT_ERRTABSIZE to be signed (it's surely small enough to fit), so
that the types match. Also move the minus sign to errval, as this is
actually what we use in the next line.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Message-Id: <20201001164630.4980-7-andre.przywara@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
With -Wsign-compare, compilers warn about a mismatching signedness in
comparisons in fdt_get_string().
Introduce a new usigned variable, which holds the actual (negated)
stroffset value, so we avoid negating all the other variables and have
proper types everywhere.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Message-Id: <20201001164630.4980-6-andre.przywara@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
With -Wsign-compare, compilers warn about a mismatching signedness
in a comparison in fdt_setprop_inplace_namelen_partial().
fdt_getprop_namelen() will only return negative error values in "proplen"
if the return value is NULL. So we can rely on "proplen" being positive
in our case and can safely cast it to an unsigned type.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Message-Id: <20201001164630.4980-5-andre.przywara@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
With -Wsign-compare, compilers warn about a mismatching signedness
in a comparison in fdt_create_with_flags().
By making hdrsize a signed integer (we are sure it's a very small
number), we avoid all the casts and have matching types.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Message-Id: <20201001164630.4980-4-andre.przywara@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
With -Wsign-compare, compilers warn about a mismatching signedness
in comparisons in fdt_move().
This stems from "bufsize" being passed in as a signed integer, even
though we would expect a buffer size to be positive.
Short of changing the prototype, check that bufsize is not negative, and
cast it to an unsigned type in the comparison.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Message-Id: <20201001164630.4980-3-andre.przywara@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
With -Wsign-compare, compilers warn about a mismatching signedness
in a comparison in fdt_add_string_().
Make all variables unsigned, and express the negative offset trick via
subtractions in the code.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Message-Id: <20201001164630.4980-2-andre.przywara@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
With -Wsign-compare, compilers warn about a mismatching signedness
in a comparison in fdt_node_offset_by_phandle().
Uses a better suited bitwise NOT operator to denote the special value of
-1, which automatically results in an unsigned type.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Message-Id: <20200921165303.9115-14-andre.przywara@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
With -Wsign-compare, compilers warn about a mismatching signedness in
a comparison in overlay_update_local_node_references().
This happens because the division of a signed int by an unsigned int
promotes the dividend to unsigned first (ANSI C standard 6.1.3.8).
As in this case we basically just divide by 4, we can do the division
separately earlier, which preserves the original type.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Message-Id: <20200921165303.9115-12-andre.przywara@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
With -Wsign-compare, compilers warn about a mismatching signedness
in a comparison in fdt_resize().
A negative buffer size will surely do us no good, so let's rule this
case out first.
In the actual comparison we then know that a cast to an unsigned type is
safe.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Message-Id: <20200921165303.9115-10-andre.przywara@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
With -Wsign-compare, compilers warn about a mismatching signedness
in a comparison in fdt_splice_().
Since we just established that oldlen is not negative, we can safely
cast it to an unsigned type.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Message-Id: <20200921165303.9115-8-andre.przywara@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
With -Wsign-compare, compilers warn about a mismatching signedness in
comparisons in fdt_get_string().
In the first two cases, we have just established that the signed values
are not negative, so it's safe to cast the values to an unsigned type.
Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Message-Id: <20200921165303.9115-7-andre.przywara@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
With -Wsign-compare, compilers warn about a mismatching signedness
in a comparison in fdt_grab_space_().
All the involved values cannot be negative, so let's switch the types of
the local variables to unsigned to make the compiler happy.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Message-Id: <20200921165303.9115-4-andre.przywara@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
With -Wsign-compare, compilers warn about a mismatching signedness
in comparisons in fdt_mem_rsv().
Since all involved values must be positive, change the used types to be
unsigned.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Message-Id: <20200921165303.9115-3-andre.przywara@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
With -Wsign-compare, compilers warn about mismatching signedness in
comparisons in fdt_offset_ptr().
This mostly stems from "offset" being passed in as a signed integer,
even though the function would not really tolerate negative values.
Short of changing the prototype, check that offset is not negative, and
use an unsigned type internally.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Message-Id: <20200921165303.9115-2-andre.przywara@arm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
fdt_check_node_offset_() checks for a valid offset but also changes the
offset by calling fdt_next_tag(). Hence, do not skip this function if
ASSUME_VALID_INPUT is set but only omit the initial offset check in that
case.
As this function works very similar to fdt_check_prop_offset_(), do the
offset check there as well depending on ASSUME_VALID_INPUT.
Message-Id: <1913141.TlUzK5foHS@noys4>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
fdt_check_header assumes that its argument points to a complete header
and can read data beyond the FDT_V1_SIZE bytes which fdt_check_full
can provide.
fdt_header_size can safely return a header size with FDT_V1_SIZE bytes
available and will return a usable value even for a corrupted header.
Signed-off-by: Patrick Oppenlander <patrick.oppenlander@gmail.com>
Message-Id: <20200709041451.338548-1-patrick.oppenlander@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Patrick Oppenlander <patrick.oppenlander@gmail.com>
Message-Id: <20200616011217.15253-1-patrick.oppenlander@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Patrick Oppenlander <patrick.oppenlander@gmail.com>
Message-Id: <20200618042117.131731-1-patrick.oppenlander@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
This condition uses bitwise OR but should be logical OR. Fix it.
Signed-off-by: Simon Glass <sjg@chromium.org>
Reported-by: kernel test robot <lkp@intel.com>
Message-Id: <20200615160033.87328-1-sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
libfdt: fix undefined behaviour in fdt_splice_()
Along the lines of commit d0b3ab0a0f ("libfdt: Fix undefined behaviour
in fdt_offset_ptr()"), fdt_splice_() similarly may not use pointer
arithmetic to do overflow checks. (The left side of the checks added by
d4c7c25c9e ["libfdt: check for potential overrun in _fdt_splice()"]
doesn't really lend itself to similar replacement though.)
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Message-Id: <f2d09e81-7cb8-c5cc-9699-1ac05b0626ff@suse.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
This error indicates a logic bug in the code calling libfdt, so VALID_DTB
is not really the right check. Update it to use VALID_INPUT instead.
Signed-off-by: Simon Glass <sjg@chromium.org>
Suggested-by: David Gibson <david@gibson.dropbear.id.au>
Message-Id: <20200302190255.51426-4-sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
If libfdt returns -FDT_ERR_INTERNAL that generally indicates a bug in the
library. Add a new assumption for these cases since it should be save to
disable these checks regardless of the input.
Signed-off-by: Simon Glass <sjg@chromium.org>
Suggested-by: David Gibson <david@gibson.dropbear.id.au>
Message-Id: <20200302190255.51426-3-sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Add a little more detail in a few of these comments.
Signed-off-by: Simon Glass <sjg@chromium.org>
Suggested-by: David Gibson <david@gibson.dropbear.id.au>
Message-Id: <20200302190255.51426-2-sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Fix 'saftey' and 'additional' typos noticed in the assumption series.
Reword the ASSUME_NO_ROLLBACK slightly to improve clarity.
Signed-off-by: Simon Glass <sjg@chromium.org>
Suggested-by: David Gibson <david@gibson.dropbear.id.au>
Message-Id: <20200302190255.51426-1-sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
This function is used to perform a full check of the device tree. Allow
it to be excluded if all assumptions are enabled.
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Message-Id: <20200220214557.176528-9-sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Add a way to remove this check and the reordering code, which is
unnecessary if the dtb is known to be correctly ordered.
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Message-Id: <20200220214557.176528-8-sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Allow enabling FDT_ASSUME_LATEST to disable version checks.
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Message-Id: <20200220214557.176528-7-sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Allow enabling FDT_ASSUME_NO_ROLLBACK to disable rolling back after a
failed operation.
Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Message-Id: <20200220214557.176528-6-sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Allow enabling ASSUME_VALID_INPUT to disable sanity checks on the device
tree and the parameters to libfdt. This assumption covers that cases where
the problem could be with either.
Signed-off-by: Simon Glass <sjg@chromium.org>
Message-Id: <20200220214557.176528-5-sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Support ASSUME_VALID_DTB to disable some sanity checks
If we assume that the DTB itself is valid then we can skip some checks and
save code space. Add various conditions to handle this.
Signed-off-by: Simon Glass <sjg@chromium.org>
Message-Id: <20200220214557.176528-4-sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Add a new ASSUME_MASK option, which allows for some control over the
checks used in libfdt. With all assumptions enabled, libfdt assumes that
the input data and parameters are all correct and that internal errors
cannot happen.
By default no assumptions are made and all checks are enabled.
Signed-off-by: Simon Glass <sjg@chromium.org>
Message-Id: <20200220214557.176528-3-sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
There does not seem to be a strong reason to inline this function. Also
we are about to add some extra code to it which will increase its size.
Move it into fdt.c and use a simple declaration in libfdt.h
Signed-off-by: Simon Glass <sjg@chromium.org>
Message-Id: <20200220214557.176528-2-sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
The overlay path ends with trailing zero. When adding this path
as property value, this character should be removed. This is the case
when the overlay adds a node with an alias.
Signed-off-by: Stefan Mavrodiev <stefan@olimex.com>
Message-Id: <20191111080444.9819-2-stefan@olimex.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
This function returns an int32_t, however the prototype in
libfdt_internal.h shows it returning an int. We haven't caught this before
because they're the same type on nearly all platforms this gets built on.
Apparently it's not the case on FreeRTOS, so someone hit this mismatch
building for that platform.
Reported-by: dharani kumar <dharanikumarsrvn@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Including libfdt.h in a C++ project fails during compilation with recent
version of GCC or Clang.
This simple example:
extern "C" {
#include <libfdt.h>
}
int main(void) { return 0; }
leads to the following errors with GCC 9.1.0:
/usr/include/libfdt.h: In function ‘void fdt32_st(void*, uint32_t)’:
/usr/include/libfdt.h:139:16: error: invalid conversion from ‘void*’ to ‘uint8_t*’ {aka ‘unsigned char*’} [-fpermissive]
139 | uint8_t *bp = property;
| ^~~~~~~~
| |
| void*
/usr/include/libfdt.h: In function ‘void fdt64_st(void*, uint64_t)’:
/usr/include/libfdt.h:163:16: error: invalid conversion from ‘void*’ to ‘uint8_t*’ {aka ‘unsigned char*’} [-fpermissive]
163 | uint8_t *bp = property;
| ^~~~~~~~
| |
| void*
This commit adds an explicit cast to uint8_t* to fix this issue.
Signed-off-by: Luc Michel <luc.michel@greensocs.com>
Message-Id: <20190910104824.1321594-1-luc.michel@greensocs.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
c12b2b0c20 "libfdt: fdt_address_cells() and fdt_size_cells()" introduced
a bug as it consolidated code between the helpers for getting
#address-cells and #size-cells. Specifically #size-cells is allowed to
be 0, and is frequently found so in practice for /cpus. IEEE1275 only
requires implementations to handle 1..4 for #address-cells, although one
could make a case for #address-cells == #size-cells == 0 being used to
represent a bridge with a single port.
While we're there, it's not totally obvious that the existing implicit
cast of a u32 to int will give the correct results according to strict C,
although it does work in practice. Straighten that up to cast only after
we've made our range checks.
Reported-by: yonghuhaige via https://github.com/dgibson/dtc/issues/28
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
In libfdt we often sanity test fdt_totalsize(fdt) fairly early, then
trust it (but *only* that header field) for the remainder of our work.
However, Coverity gets confused by this - it sees the byteswap in
fdt32_ld() and assumes that means it is coming from an untrusted source
everytime, resulting in many tainted data warnings.
Most of these end up with logic in fdt_get_string() as the unsafe
destination for this tainted data, so let's tweak the logic there to make
it clearer to Coverity that this is ok.
We add a sanity test on fdt_totalsize() to fdt_probe_ro_(). Because the
interface allows bare ints to be used for offsets, we already have the
assumption that totalsize must be 31-bits or less (2GiB would be a
ludicrously large fdt). This makes this more explicit.
We also make fdt_probe_ro() return the size for convenience, and change the
logic in fdt_get_string() to keep it in a local so that Coverity can see
that it has already been bounds-checked.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Georg Kotheimer