[Bug sanitizer/98609] sanitizer diagnoses VLAs with length zero although zero-length arrays are a GNU extension
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98609 --- Comment #9 from Martin Uecker --- I just ran into this problem again while trying to fix PR98608 where the problem is that instrumentation of parameters is missing. In parameters people often use n == 0 null and some of the -Wnonnull warnings we have currently even require setting it 0.
[Bug sanitizer/98609] sanitizer diagnoses VLAs with length zero although zero-length arrays are a GNU extension
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98609 Martin Sebor changed: What|Removed |Added CC||msebor at gcc dot gnu.org --- Comment #8 from Martin Sebor --- Zero allocations should be diagnosed by -Walloc-zero. The option is disabled by default to avoid false positives for calls to malloc(0) emitted by GCC in some cases. The test case in comment #0 isn't diagnosed even when -Walloc-zero is explicitly set is a bug. It should be diagnosed, and I think for VLAs the warning should be enabled in -Wall to help detect potential aliasing violations). Some uses of zero length arrays that aren't VLAs are diagnosed by -Wzero-length-bounds (enabled by -Warray-bounds). I posted a patch in November to enhance their detection, including VLAs, but it never got reviewed. I expect to resubmit it for GCC 12. With that patch, the test case in comment #0 is diagnosed as long as the array is either accessed or passed as an argument to a function that might use it.
[Bug sanitizer/98609] sanitizer diagnoses VLAs with length zero although zero-length arrays are a GNU extension
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98609 --- Comment #7 from Martin Liška --- (In reply to Jakub Jelinek from comment #6) > That is not really possible, as the compiler assumes for > -fno-sanitize-recover=vla which is not the default value/ > that when we call the library routine, it never > returns (it is noreturn). Then it can be allowed only for recover UBSAN entry points.
[Bug sanitizer/98609] sanitizer diagnoses VLAs with length zero although zero-length arrays are a GNU extension
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98609 --- Comment #6 from Jakub Jelinek --- That is not really possible, as the compiler assumes for -fno-sanitize-recover=vla that when we call the library routine, it never returns (it is noreturn).
[Bug sanitizer/98609] sanitizer diagnoses VLAs with length zero although zero-length arrays are a GNU extension
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98609 --- Comment #5 from Martin Liška --- I would recommend changing just libsanitizer to allow something like UBSAN_OPTIONS=vla_bounds_allow_zero=1. Should be relatively small change.
[Bug sanitizer/98609] sanitizer diagnoses VLAs with length zero although zero-length arrays are a GNU extension
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98609 --- Comment #4 from Jakub Jelinek --- I'd say it is similar with shifts, the diagnostics about the shift count being negative or too large is highly useful, the diagnostics about the various lshift properties shifting into sign bit or shifting left negative values etc.) are pedantic, at least GCC doesn't really take any advantage of that, because there are so many different variants of the restrictions. But for shifts we indeed do have a way to selectively turn one or the other on or off. So perhaps -fsanitize=vla can be a union of two subooptions too. Though, we can't really do anything about this until upstream libsanitizer is changed, because the diagnostics comes from that library. And it would be really confusing to just do this on the GCC side, allow VLA checks of <= 0 (=vla), < 0 (=vla-negative), == 0 (=vla-zero) and use the same library routine in all cases that would always talk about non-positive value.
[Bug sanitizer/98609] sanitizer diagnoses VLAs with length zero although zero-length arrays are a GNU extension
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98609 --- Comment #3 from Martin Uecker --- Fair enough. But there is also no way to selectively turn it off (or I am not aware of it). The warning for < 0 is important and useful while the warning for == 0 is pedantic and not useful by itself when we generally allow zero sized arrays elsewhere.
[Bug sanitizer/98609] sanitizer diagnoses VLAs with length zero although zero-length arrays are a GNU extension
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98609 --- Comment #2 from Jakub Jelinek --- The sanitizers generally diagnose what the C or C++ language spec say, not what the various extensions allow, it is the same also for shifts etc. So I think it is correct that this is diagnosed by default.
[Bug sanitizer/98609] sanitizer diagnoses VLAs with length zero although zero-length arrays are a GNU extension
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98609 Martin Liška changed: What|Removed |Added Ever confirmed|0 |1 CC||mpolacek at gcc dot gnu.org Status|UNCONFIRMED |NEW Last reconfirmed||2021-01-11 --- Comment #1 from Martin Liška --- Confirmed. @Marek: Can you please take a look?
