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

Mon Feb 17 12:25:54 PST 2020

It looks like I wasn't careful and mixed version. I compiled with clang-9
but used lldb-6. Surprisingly this was the only error I notice when mixing
these version. I could swear I tried compiling with clang-6. I'd double
check but it appears that installing lldb-9 removed lldb(-6) from my system
Thanks for pointing me in the right direction

On Mon, Feb 17, 2020 at 11:18 AM Adrian Prantl <aprantl at apple.com> wrote:

> 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.
> >>
> >> _______________________________________________
> >> LLVM Developers mailing list
> >> llvm-dev at lists.llvm.org
> >> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
>
>
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