Re: gdb problems with -O1 on x86_64 architecture.

[Tigran Aivazian <tigran at veritas dot com>]

Hi,

I thought it is worth showing how it behaves on -O2 compiled binary as 
well:

# gcc -g -Wall -O2 -fno-optimize-sibling-calls uvar.c -o uvar-O2

(gdb) b kt_func3
Breakpoint 1 at 0x4004e0: file uvar.c, line 11.
(gdb) r
Starting program: /root/mod/uvar-O2

Breakpoint 1, kt_func3 (x1=0x11111133, x2=0x22222244, x3=0x33333355, 
x4=0x44444466, x5=0x55555577, x6=0x66666688,
    x7=0x77777799, x8=0x888888aa, x9=0x9566b560) at uvar.c:11
11              return (x1 + x2 + x3/2 + x4/4 + x5/5 + x6/6 + x7/7 + x8/8 
+ x9/9);
(gdb) bt
#0  kt_func3 (x1=0x11111133, x2=0x22222244, x3=0x33333355, x4=0x44444466, 
x5=0x55555577, x6=0x66666688, x7=0x77777799,
    x8=0x888888aa, x9=0x9566b560) at uvar.c:11
#1  0x00000000004005d3 in kt_func2 (x1=<value optimized out>, x2=<value 
optimized out>, x3=<value optimized out>,
    x4=<value optimized out>, x5=<value optimized out>, x6=<value 
optimized out>, x7=0x77777788, x8=0x88888899,
    x9=0x999999aa) at uvar.c:16
#2  0x0000000000400623 in kt_func1 (x1=<value optimized out>, x2=<value 
optimized out>, x3=<value optimized out>,
    x4=<value optimized out>, x5=<value optimized out>, x6=<value 
optimized out>, x7=0x77777777, x8=0x88888888,
    x9=0x99999999) at uvar.c:22
#3  0x000000000040067a in main (argc=<value optimized out>, argv=<value 
optimized out>) at uvar.c:30

As you see, it claims that x1,x2,x3,x4,x5,x6 are optimized out and 
x7,x8,x9 are available and shows the correct values. This is for kt_func2 
and kt_func1 functions, but for kt_func3 it shows all values correctly 
except the last one --- x9 is garbage. But with -O0 it shows everything 
correctly.

I attached the -O2 compiled uvar as well.

Kind regards
Tigran

Attachment: uvar-O2
Description: uvar-O2