[llvm-dev] Have the debugger show an away with a dynamic size?
Adrian Prantl via llvm-dev
llvm-dev at lists.llvm.org
Mon Feb 17 12:27:58 PST 2020
I added the VLA support to clang and lldb about a year ago, so you'll need fairly recent version of both for it to work.
-- adrian
> On Feb 17, 2020, at 12:25 PM, Levo DeLellis <levo.delellis at gmail.com> wrote:
>
> 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 <mailto: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 <mailto: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 <mailto: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 <mailto: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 <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 <mailto:llvm-dev at lists.llvm.org>
> >> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev <https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
> >
>
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