+U-Boot, Tom, Masahiro Hi David, On 10 April 2018 at 01:22, David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> wrote: > On Wed, Apr 04, 2018 at 01:21:10AM +0800, Simon Glass wrote: >> Hi David, >> >> On 3 April 2018 at 23:02, David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> wrote: >> > >> > On Fri, Mar 30, 2018 at 04:42:21PM +0800, Simon Glass wrote: >> > > Hi David, >> > > >> > > On 26 March 2018 at 07:25, David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> wrote: >> > > > fdt_string() is used to retrieve strings from a DT blob's strings section. >> > > > It's rarely used directly, but is widely used internally. >> > > > >> > > > However, it doesn't do any bounds checking, which means in the case of a >> > > > corrupted blob it could access bad memory, which libfdt is supposed to >> > > > avoid. >> > > > >> > > > This write a safe alternative to fdt_string, fdt_get_string(). It checks >> > > > both that the given offset is within the string section and that the string >> > > > it points to is properly \0 terminated within the section. It also returns >> > > > the string's length as a convenience (since it needs to determine to do the >> > > > checks anyway). >> > > > >> > > > fdt_string() is rewritten in terms of fdt_get_string() for compatibility. >> > > > >> > > > Most of the diff here is actually testing infrastructure. >> > > > >> > > > Signed-off-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> >> > > > --- >> > > > libfdt/fdt_ro.c | 61 +++++++++++++++++++++++++++++++++++-- >> > > > libfdt/libfdt.h | 18 ++++++++++- >> > > > libfdt/version.lds | 2 +- >> > > > tests/.gitignore | 1 + >> > > > tests/Makefile.tests | 2 +- >> > > > tests/run_tests.sh | 1 + >> > > > tests/testdata.h | 1 + >> > > > tests/testutils.c | 11 +++++-- >> > > > tests/trees.S | 26 ++++++++++++++++ >> > > > tests/truncated_string.c | 79 ++++++++++++++++++++++++++++++++++++++++++++++++ >> > > > 10 files changed, 193 insertions(+), 9 deletions(-) >> > > > create mode 100644 tests/truncated_string.c >> > > >> > > Similar code-size quesiton here. It looks like a lot of checking code. >> > > Can we have an option to remove it? >> > >> > Again, I'm disinclined without a concrete example of a problem. Fwiw >> > the code size change is +276 bytes on my setup. >> >> That might not sound like a lot, but the overhead of DT in U-Boot is >> about 3KB, so this adds nearly 10%. > > Hm. And how much is it compared to the whole U-Boot blob? > >> The specific problem is that when U-Boot SPL gets too big boards don't >> boot. Because we take the upstream libfdt this will affect U-Boot. >> >> Do you have any thoughts on how we could avoid this size increase? > > So, again, I'm very disinclined to prioritize size over memory safety > without a *concrete* example. i.e. "We hit this specific problem with > size on this specific board that we were really using" rather than > just "it might be a problem". > > IMO, thinking of it in terms of the "increase" is the wrong way > arond. If size is really a problem for you, you want to consider how > you can reduce it in any way, not just rolling back the most recent > changes. The most obvious one to me would be to try > -ffunction-sections to exclude any functions that aren't actually used > by u-boot (if this is helpful and the compiler's an issue, I'd be > willing to consider splitting up libfdt into a bunch more C files). Actually U-Boot does use that option. Believe me, a lot of work has gone into making this small. There is constant pressure to reduce/retain the size in SPL so that we can stay below limits. E.g. firefly-rk3288 has a 30KB limit for SPL. Current problems are the 64-bit Allwinner parts which are right up against the limit at present. Also, Masahiro recently did some work to make U-Boot's version of libfdt the same as is used by Linux, so any changes will impact us quite quickly. Regards, Simon -- To unsubscribe from this list: send the line "unsubscribe devicetree-compiler" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
