[llvm-bugs] [Bug 35049] New: [PowerPC] backtrace isn't complete
via llvm-bugs
llvm-bugs at lists.llvm.org
Mon Oct 23 20:57:02 PDT 2017
https://bugs.llvm.org/show_bug.cgi?id=35049
Bug ID: 35049
Summary: [PowerPC] backtrace isn't complete
Product: new-bugs
Version: trunk
Hardware: Other
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: new bugs
Assignee: unassignedbugs at nondot.org
Reporter: eric.schweitz at pgroup.com
CC: llvm-bugs at lists.llvm.org
If we take a rather simple program like the following and compile it with
"clang -g -O0 prgm.c", we don't appear to get debug stack frame information
that covers all instructions.
% gdb a.out
Reading symbols from a.out...done.
(gdb) b foo
Breakpoint 1 at 0x1000062c: file backtrace.c, line 12.
(gdb) r
Starting program: ./a.out
Breakpoint 1, foo () at backtrace.c:12
12 return bar() * 2;
(gdb) disas
Dump of assembler code for function foo:
0x0000000010000610 <+0>: lis r2,4099
0x0000000010000614 <+4>: addi r2,r2,-32512
0x0000000010000618 <+8>: mflr r0
0x000000001000061c <+12>: std r31,-8(r1)
0x0000000010000620 <+16>: std r0,16(r1)
0x0000000010000624 <+20>: stdu r1,-112(r1)
0x0000000010000628 <+24>: mr r31,r1
=> 0x000000001000062c <+28>: bl 0x100005f0 <bar>
0x0000000010000630 <+32>: nop
0x0000000010000634 <+36>: li r4,1
0x0000000010000638 <+40>: slw r3,r3,r4
0x000000001000063c <+44>: extsw r3,r3
0x0000000010000640 <+48>: addi r1,r1,112
0x0000000010000644 <+52>: ld r0,16(r1)
0x0000000010000648 <+56>: ld r31,-8(r1)
0x000000001000064c <+60>: mtlr r0
0x0000000010000650 <+64>: blr
0x0000000010000654 <+68>: .long 0x0
0x0000000010000658 <+72>: .long 0x0
0x000000001000065c <+76>: .long 0x0
End of assembler dump.
(gdb) b *0x000000001000064c
Breakpoint 2 at 0x1000064c: file backtrace.c, line 12.
(gdb) bt
#0 foo () at backtrace.c:12
#1 0x000000001000069c in main () at backtrace.c:20
(gdb) cont
Continuing.
Breakpoint 2, 0x000000001000064c in foo () at backtrace.c:12
12 return bar() * 2;
(gdb) bt
#0 0x000000001000064c in foo () at backtrace.c:12
#1 0x00001000000a4700 in generic_start_main.isra () from /lib64/libc.so.6
#2 0x00001000000a48f4 in __libc_start_main () from /lib64/libc.so.6
#3 0x0000000000000000 in ?? ()
(gdb)
As can be seen in the above cut-and-paste, the backtrace for breakpoint 1 and
the backtrace fro breakpoint 2 are different even though they are in the same
function, foo().
Here is an example program:
"""
#include <stdio.h>
__attribute__((noinline))
int bar()
{
return 1;
}
__attribute__((noinline))
int foo()
{
return bar() * 2;
}
int main()
{
int i = 100;
while (i > 0)
{
printf("result = %d\n", foo());
i--;
}
return 0;
}
"""
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