Const pointer with large array size

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1

Hey, please could you help me to understand what is the expected behaviour of code snippet bellow?

const t: *const [1000]u8 = "asdf";
std.debug.print("string: {s}\n", .{t});

I’m using a scaffold build file from zig init, and using zig build && ./zig-out/bin/main to test it.

Compilation is fine with no errors. Should I get a panic instead or it’s expected?

I do see different kind of overflow data :grinning: depends on release mode. Please see few examples:

Buil type cmd Output
zig build string: asdfinteger overflowattempt to cast negative value to unsigned integerh�Fstring: {s} invalid error codethread {} panic: {s} Panicked during a panic. Aborting. (msg truncated)@memcpy arguments aliasswitch on corrupt valueunable to install segfault handler, maybe adjust have_segfault_handling_support in std/debug.zigreached unreachable codeDeadlock detectedincorrect alignment’noreturn’ function returnedattempt to use null valueinteger cast truncated bitscast causes pointer to be null__TEXT__unwind_info__eh_frame{s}:{d}:{d}???:?:?: 0x{x} in {s} ({s}) ^???for loop over objects with non-equal lengths@memcpy arguments have non-equal lengths__DWARF__debug_info__debug_abbrev__debug_str__debug_str_offsets__debug_line__debug_line_str__debug_ranges__debug_loclists__debug_rnglists__debug_addr__debug_names__debug_frame__eh_frame_h
zig build --release=small string: asdf00010203040506070809101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899OperationNotSupported 8888@��0��04X���� t
zig build --release=fast string: asdf(msg truncated)failed to set noop SIGPIPE handler: {s}00010203040506070809101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899OperationNotSupportedDiskQuotaFileTooBigInputOutputNoSpaceLeftDeviceBusyInvalidArgumentAccessDeniedBrokenPipeSystemResourcesOperationAbortedNotOpenForWritingLockViolationWouldBlockConnectionResetByPeerUnexpectedOverflowInvalidUtf8Utf8ExpectedContinuationUtf8OverlongEncodingUtf8EncodesSurrogateHalfUtf8CodepointTooLargeUtf8InvalidStartByteTruncatedInputUtf8CannotEncodeSurrogateHalfCodepointTooLargeMissingDebugInfoUnsupportedOperatingSystemInvalidDebugInfoOutOfMemorySharingViolationPathAlreadyExistsFileNotFoundPipeBusyNameTooLongInvalidWtf8BadPathNameNetworkNotFoundAntivirusInterferenceSymLinkLoopProcessFdQuotaExceededSystemFdQuotaExceededNoDeviceIsDirNotDirFileLocksNotSupportedFileBusy
zig build --release=safe string: asdf__TEXT__unwind_info__eh_frame__DWARF__debug_info__debug_abbrev__debug_str__debug_str_offsets__debug_line__debug_line_str__debug_ranges__debug_loclists__debug_rnglists__debug_addr__debug_names__debug_frame__eh_frame_hdr(msg truncated)failed to set noop SIGPIPE handler: {s}00010203040506070809101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899OperationNotSupportedDiskQuotaFileTooBigInputOutputNoSpaceLeftDeviceBusyInvalidArgumentAccessDeniedBrokenPipeSystemResourcesOperationAbortedNotOpenForWritingLockViolationWouldBlockConnectionResetByPeerUnexpectedMissingDebugInfoUnsupportedOperatingSystemInvalidDebugInfoOutOfMemorySharingViolationPathAlreadyExistsFileNotFoundPipeBusyNameTooLongInvalidUtf8InvalidWtf8BadPathNameNetworkNotFoundAntivirusInterferenceSymLinkLoopProcessFdQuotaExc

Many thanks in advance.

Best,
Felipe

2

It should give you a compiler error, something like

test.zig:10:29: error: expected type '*const [1000]u8', found '*const [4:0]u8'
 const t: *const [1000]u8 = "asdf";
                            ^~~~~~

This looks like it could be a compiler bug.
What version of zig you are using?

3

@IntegratedQuantum I’m using 0.12.0 installed by homebrew.

$ zig version
0.12.0

$ sw_vers
ProductName:		macOS
ProductVersion:		14.4.1
BuildVersion:		23E224
4

btw I was expecting an compiler error like you’ve sent. Currently I’m using on MacOS ARM M1 arch.

Have you using same version but diff arch probably?

5

I was using a slightly older version (0.12.0-dev.3518+d2be725e4).
I just tried zig 0.12 and I get the same behavior.

6

It’s probably best if you report this on github.

7

Yeah, I’m actually doing that right now… afterwards I’ll post the link over here.

Many thanks for the confirmation @IntegratedQuantum .

8

Yes, it’s a bug.

This compiles and panics (since 995 bytes are undefined):

    const ts: *const [4:0]u8 = &[4:0]u8{ 'a', 's', 'd', 'f' };
    const t: *const [1000]u8 = ts;

This does not compile:

    const ts: *const [4]u8 = &[4]u8{ 'a', 's', 'd', 'f' };
    const t: *const [1000]u8 = ts;

error: expected type '*const [1000]u8', found '*const [4]u8'

1 Like
9

Many thanks for confirming this @dimdin and to catch it by other example, which doesn’t not compile here as well.

10

Bug reported it.

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