[llvm-dev] Have the debugger show an away with a dynamic size?

[Adrian Prantl via llvm-dev]

That is interesting. According to LLDB's test/lang/c/vla/* frame variable for a VLA is supposed to work. Frame variable is also supposed to hide the __vla_expr0 artificial helper variable. Is this an older LLDB from your system or an LLDB you built from source? If yes, would you mind filing a bugreport about this?

thanks,
adrian

> On Feb 15, 2020, at 8:17 AM, Levo DeLellis <levo.delellis at gmail.com> wrote:
> 
> Thanks for the suggestions but it doesn't appear to be working correctly for me. I tried building the below after seeing the results with "clang -g -std=c99 test.c" and got the same result
> 
> LLDB thinks MyArray is 81 elements long even though 81 and 80 doesn't show up anywhere in the llvm-ir (I tried again using an llvm ir file made by clang -g -std=c99 test.c -S -emit-llvm and clang -g test.ll)
> 
> $ cat test.c
> int foo(int s) {
>     int MyArray[s];
>     int i;
>     for (i = 0; i < s; ++i)
>         MyArray[i] = s;
>     return 0;
> }
> 
> int main(){
>     foo(5);
>     return 0;
> }
> $ clang -g test.c 
> $ lldb ./a.out 
> (lldb) target create "./a.out"
> Current executable set to './a.out' (x86_64).
> (lldb) break set -f test.c -l 6
> Breakpoint 1: where = a.out`foo + 101 at test.c:7, address = 0x0000000000400505
> (lldb) r
> Process 3205 launched: './a.out' (x86_64)
> Process 3205 stopped
> * thread #1, name = 'a.out', stop reason = breakpoint 1.1
>     frame #0: 0x0000000000400505 a.out`foo(s=5) at test.c:7
>    4      for (i = 0; i < s; ++i)
>    5          MyArray[i] = s;
>    6      return 0;
> -> 7   }
>    8   
>    9   int main(){
>    10      foo(5);
> (lldb) frame variable
> (int) s = 5
> (unsigned long) __vla_expr0 = 5
> (int) i = 5
> (int [81]) MyArray = {
>   [0] = 5
>   [1] = 5
>   [2] = 5
>   [3] = 5
>   [4] = 5
>   [5] = 0
>   [6] = -136481184
>   [7] = 32767
>   [8] = -8408
>   [9] = 32767
>   [10] = -8544
>   [11] = 32767
>   [12] = 1
>   [13] = 5
>   [14] = 5
>   [15] = 0
>   [16] = -8512
>   [17] = 32767
>   [18] = 0
>   [19] = 5
>   [20] = -8432
>   [21] = 32767
>   [22] = 4195641
>   [23] = 0
>   [24] = -8208
>   [25] = 32767
>   [26] = 0
>   [27] = 0
>   [28] = 4195664
>   [29] = 0
>   [30] = -140485737
>   [31] = 32767
>   [32] = 0
>   [33] = 32
>   [34] = -8200
>   [35] = 32767
>   [36] = 0
>   [37] = 1
>   [38] = 4195616
>   [39] = 0
>   [40] = 0
>   [41] = 0
>   [42] = -1953144313
>   [43] = 1284291557
>   [44] = 4195248
>   [45] = 0
>   [46] = -8208
>   [47] = 32767
>   [48] = 0
>   [49] = 0
>   [50] = 0
>   [51] = 0
>   [52] = 1064657415
>   [53] = -1284291430
>   [54] = 933978631
>   [55] = -1284287451
>   [56] = 0
>   [57] = 32767
>   [58] = 0
>   [59] = 0
>   [60] = 0
>   [61] = 0
>   [62] = -136423629
>   [63] = 32767
>   [64] = -136530376
>   [65] = 32767
>   [66] = 386784
>   [67] = 0
>   [68] = 0
>   [69] = 0
>   [70] = 0
>   [71] = 0
>   [72] = 0
>   [73] = 0
>   [74] = 4195248
>   [75] = 0
>   [76] = -8208
>   [77] = 32767
>   [78] = 4195290
>   [79] = 0
>   [80] = -8216
> }
> 
> 
> On Thu, Feb 13, 2020 at 3:53 PM Adrian Prantl <aprantl at apple.com> wrote:
> Take a look at the IR clang produces for C99 variable-length arrays.
> 
> -- adrian
> 
>> On Feb 13, 2020, at 10:03 AM, Levo DeLellis via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>> 
>> Hi. I searched and the closest thing I could find was this http://lists.llvm.org/pipermail/llvm-dev/2018-February/121348.html
>> 
>> Currently a known sized array looks and debugs as expected. I use llvm.dbg.declare with DICompositeType tag: DW_TAG_array_type and the size field. In my language arrays are always passed around with a pointer and size pair. I'd like debugging to show up as nicely instead of a pointer addr with no information about the elements. How would I do this? I don't use the C API, I output llvm-ir directly. I was hoping I can call llvm.dbg.declare/addr/value to specify the pointer, name and size of the variable but I really have no idea how to pass the size to the debugger.
>> 
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