Using "slow-stepping" doesn't fix the issue. It appears that the debugger
is setting some flags when hitting the breakpoint and stepping which
prohibit the intrinsic to evaluate the conditionals properly.
On Thu, Dec 11, 2014 at 8:25 PM, Greg Clayton <gclay...@apple.com> wrote:
>
> Does this work if you first type:
>
> (lldb) setting set target.use-fast-stepping false
>
> Then step?
>
>
> > On Dec 11, 2014, at 1:38 AM, Mario Zechner <badlogicga...@gmail.com>
> wrote:
> >
> > Hi,
> >
> > we are running into a problem with the __sync_bool_compare_and_swap
> intrinsic on ARM. Trying to step over the call to
> __sync_bool_compare_and_swap will put LLDB into a sort of infinite loop.
> >
> > This is reproduceable in the latest XCode (6.1.1 (6A2008a)). Create an
> iOS project with the following main function:
> >
> > int main(int argc, char * argv[]) {
> > int c = 0;
> > while(1) {
> > if(__sync_bool_compare_and_swap(&c, 0, 1)) {
> > break;
> > }
> > }
> > printf("%d\n", c);
> > }
> >
> > The intrinsic compiles down to:
> >
> > 0xb7010: dmb ish
> > 0xb7014: movs r0, #0x1
> > 0xb7016: movs r1, #0x0
> > 0xb7018: add r2, sp, #0x14
> > 0xb701a: str r0, [sp, #0x10]
> > 0xb701c: str r1, [sp, #0xc]
> > 0xb701e: str r2, [sp, #0x8]
> > -> 0xb7020: ldr r0, [sp, #0x8]
> > 0xb7022: ldrex r1, [r0]
> > 0xb7026: ldr r2, [sp, #0xc]
> > 0xb7028: cmp r1, r2
> > 0xb702a: str r1, [sp, #0x4]
> > 0xb702c: bne 0xb703a ; main + 62 at main.m:15
> > 0xb702e: ldr r1, [sp, #0x10]
> > 0xb7030: ldr r2, [sp, #0x8]
> > 0xb7032: strex r0, r1, [r2]
> > 0xb7036: cmp r0, #0x0
> > 0xb7038: bne 0xb7020 ; main + 36 at main.m:15
> > 0xb703a: dmb ish
> >
> > When stepping over, LLDB will first set a breakpoint on 0xb702c: bne
> 0xb703a. Next it executes a single step, moving PC to 0xb702e: ldr
> r1, [sp, #0x10] as the condition is not meet.
> >
> > LLDB then sets a breakpoint on the next branch instruction at 0xb7038:
> bne 0xb7020. It single steps the instruction, the condition is meet, and
> we end up at 0xb7020 again.
> >
> > The code never breaks out of this loop, LLDB will continue to set the
> breakpoints indefinitely.
> >
> > Any idea how to fix this?
> >
> > Thanks,
> > Mario
> > _______________________________________________
> > lldb-dev mailing list
> > lldb-dev@cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/lldb-dev
>
>
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