Wrong debug info for break at -O1


Bugzilla Link	PR46041
Status	NEW
Importance	P enhancement
Reported by	Yibiao Yang (yangyibiao@nju.edu.cn)
Reported on	2020-05-22 09:12:47 -0700
Last modified on	2020-05-22 10:43:37 -0700
Version	trunk
Hardware	PC Linux
CC	jdevlieghere@apple.com, keith.walker@arm.com, llvm-bugs@lists.llvm.org, paul_robinson@playstation.sony.com
Fixed by commit(s)
Attachments	`a.out` (17440 bytes, application/x-executable)
Blocks
Blocked by
See also

Created attachment 23523
the binary

$ clang --version
clang version 11.0.0 (/home/yibiao/.cache/yay/llvm-git/llvm-project
871beba234a83a2a02da9dedbd59b91a1bfbd7af)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

$ lldb --version
lldb version 11.0.0
  clang revision 871beba234a83a2a02da9dedbd59b91a1bfbd7af
  llvm revision 871beba234a83a2a02da9dedbd59b91a1bfbd7af

$ clang -O1 -g small.c

$ lldb a.out
(lldb) target create "a.out"
Current executable set to '/home/yibiao/Debugger/a.out' (x86_64).
(lldb) b 5
Breakpoint 1: where = a.out`f + 21 at small.c:5:1, address = 0x0000000000401125
(lldb) r
Process 46982 launched: '/home/yibiao/Debugger/a.out' (x86_64)
Process 46982 stopped
* thread #1, name = 'a.out', stop reason = breakpoint 1.1
    frame #0: 0x0000000000401125 a.out`f(x=-216) at small.c:5:1
   2      if (x==-216 || x==-132)
   3         return 1;
   4      return 0;
-> 5    }
   6
   7    int main () {
   8      volatile int i;
(lldb) fr var x
(int) x = -216
(lldb)

/************************************
As showed, when setting breakpoint on Line 5 (first hit), the value of "x" is -
216.
However, when step-i to Line 5, the value of "x" is -230 which is as expected:
************************************/

$ clang -O1 -g small.c; lldb a.out
(lldb) target create "a.out"
Current executable set to '/home/yibiao/Debugger/a.out' (x86_64).
(lldb) b main
Breakpoint 1: where = a.out`main + 5 at small.c:9:10, address =
0x0000000000401135
(lldb) r
Process 45549 launched: '/home/yibiao/Debugger/a.out' (x86_64)
Process 45549 stopped
* thread #1, name = 'a.out', stop reason = breakpoint 1.1
    frame #0: 0x0000000000401135 a.out`main at small.c:9:10
   6
   7    int main () {
   8      volatile int i;
-> 9      for (i = -230; i < -120; i++)
   10       if (f(i) != (i==-216 || i==-132))
   11         return 1;
   12     return 0;
(lldb) si -c 14
Process 45549 stopped
* thread #1, name = 'a.out', stop reason = instruction step into
    frame #0: 0x0000000000401128 a.out`f(x=-230) at small.c:5:1
   2      if (x==-216 || x==-132)
   3         return 1;
   4      return 0;
-> 5    }
   6
   7    int main () {
   8      volatile int i;
(lldb) fr var x
(int) x = -230
(lldb)

/******************* the small.c *************/

$ cat small.c
int f(int x) {
  if (x==-216 || x==-132)
     return 1;
  return 0;
}

int main () {
  volatile int i;
  for (i = -230; i < -120; i++)
    if (f(i) != (i==-216 || i==-132))
      return 1;
  return 0;
}

Quuxplusone / LLVMBugzillaTest

Wrong debug info for break at -O1 #45011