<value optimized out> even with gcc -g -O0

[Chuck Anderson]

I'm trying to debug an issue for the upstream author of ocp and am
running into an issue where gdb is showing "<value optimized out>" for
variables even though I've compiled the program with gcc -g -O0. Are
there any gcc/gdb gurus who can help?

Compiler excerpts:

gcc -g -O0 -fPIC -Wall -I.././ -I.././gnulib kickload.c -o kickload.o -c
gcc -g -O0 -fPIC -Wall -I.././ -I.././gnulib compdate.c -o compdate.o -c
...
gcc -g -O0 -fPIC -Wall -I./ -I./gnulib -o ocp boot/kickload.o -pthread -ldl goodies/helpc/ocphhc doc/opencp.dox ocp.hlp

gdb output:

Program received signal SIGSEGV, Segmentation fault.
playmonoi16 (dst=0x76ddc0, len=<value optimized out>,
ch=<value optimized out>) at mixasm.c:1746
1746 *(dst++)+=voltabs[0]
(gdb) p dst
$1 = (int32_t *) 0x76ddc0
(gdb) p len
$2 = <value optimized out>
(gdb) p ch
$3 = <value optimized out>
(gdb) p *ch
Cannot access memory at address 0x0
(gdb) up
#1 0x00007ffff5948257 in mixPlayChannel (dst=<value optimized out>,
len=<value optimized out>, ch=0x779df0, stereo=<value optimized
out>)
at mixasm.c:2022
2022 playrout(dst, mylen, ch);
(gdb) p stereo
$4 = <value optimized out>


Thanks!

[Gianluca Sforna]

Post by Chuck Anderson
Program received signal SIGSEGV, Segmentation fault.
playmonoi16 (dst=0x76ddc0, len=<value optimized out>,
? ?ch=<value optimized out>) at mixasm.c:1746

Sorry for asking the obvious, but this hit me several times... is this
mixasm.c file part of the sources you are compiling with -g -O0? if
it's in a library your code is using, you also need to recompile that
one with -O0.

[Chuck Anderson]

Post by Gianluca Sforna

Post by Chuck Anderson
Program received signal SIGSEGV, Segmentation fault.
playmonoi16 (dst=0x76ddc0, len=<value optimized out>,
? ?ch=<value optimized out>) at mixasm.c:1746

Sorry for asking the obvious, but this hit me several times... is this
mixasm.c file part of the sources you are compiling with -g -O0? if
it's in a library your code is using, you also need to recompile that
one with -O0.

Yup, it is part of the source. Many/most of the files are actually
compiled as shared objects, but everything is using -g -O0. Someone
on #gdb thinks this is a gcc bug.

[Roberto Ragusa]

Post by Chuck Anderson

Post by Gianluca Sforna

Post by Chuck Anderson
Program received signal SIGSEGV, Segmentation fault.
playmonoi16 (dst=0x76ddc0, len=<value optimized out>,
ch=<value optimized out>) at mixasm.c:1746

Sorry for asking the obvious, but this hit me several times... is this
mixasm.c file part of the sources you are compiling with -g -O0? if
it's in a library your code is using, you also need to recompile that
one with -O0.

Yup, it is part of the source. Many/most of the files are actually
compiled as shared objects, but everything is using -g -O0. Someone
on #gdb thinks this is a gcc bug.

One thing I would try is adding a

int *lenp=&len;

somewhere, just to make optimization a little more difficult for gcc.
Maybe you avoid the bug, if there is one.

[David Malcolm]

Post by Chuck Anderson
I'm trying to debug an issue for the upstream author of ocp and am
running into an issue where gdb is showing "<value optimized out>" for
variables even though I've compiled the program with gcc -g -O0. Are
there any gcc/gdb gurus who can help?
gcc -g -O0 -fPIC -Wall -I.././ -I.././gnulib kickload.c -o kickload.o -c
gcc -g -O0 -fPIC -Wall -I.././ -I.././gnulib compdate.c -o compdate.o -c
...
gcc -g -O0 -fPIC -Wall -I./ -I./gnulib -o ocp boot/kickload.o -pthread -ldl goodies/helpc/ocphhc doc/opencp.dox ocp.hlp
Program received signal SIGSEGV, Segmentation fault.
playmonoi16 (dst=0x76ddc0, len=<value optimized out>,
ch=<value optimized out>) at mixasm.c:1746
1746 *(dst++)+=voltabs[0]
(gdb) p dst
$1 = (int32_t *) 0x76ddc0
(gdb) p len
$2 = <value optimized out>
(gdb) p ch
$3 = <value optimized out>
(gdb) p *ch
Cannot access memory at address 0x0
(gdb) up
#1 0x00007ffff5948257 in mixPlayChannel (dst=<value optimized out>,
len=<value optimized out>, ch=0x779df0, stereo=<value optimized
out>)
at mixasm.c:2022
2022 playrout(dst, mylen, ch);
(gdb) p stereo
$4 = <value optimized out>

Not sure if it's the same bug, but I ran into similar issue when trying
to debug Python; see:
https://bugzilla.redhat.com/show_bug.cgi?id=556975
"Variables optimized out (python)"

Hope this is helpful
Dave

[Jan Kratochvil]

Post by Chuck Anderson
I'm trying to debug an issue for the upstream author of ocp and am
running into an issue where gdb is showing "<value optimized out>" for
variables even though I've compiled the program with gcc -g -O0.

[...]

Post by Chuck Anderson
gcc -g -O0 -fPIC -Wall -I.././ -I.././gnulib kickload.c -o kickload.o -c
gcc -g -O0 -fPIC -Wall -I.././ -I.././gnulib compdate.c -o compdate.o -c
...
gcc -g -O0 -fPIC -Wall -I./ -I./gnulib -o ocp boot/kickload.o -pthread -ldl goodies/helpc/ocphhc doc/opencp.dox ocp.hlp

If you list also the mixasm.c compilation line you would find:
gcc -g -O0 -fpic -Wall -I.././ -O mixasm.c -o mixasm.o -c

as there is explicit -O in dev/Makefile there. After removing it getting
a valid dump with no <value optimized out>.

For the -O build found one <value optimized out> as correct and one <value
optimized out> as some bug in either gdb or gcc but that is out of the scope
of this mail thread. -O0 -g works, NOTABUG.


Thanks,
Jan

#0 playmonoi16 (dst=0x71ff90, len=384, ch=0x72bfc0) at mixasm.c:1738
#1 0x00007ffff5d57cc7 in mixPlayChannel (dst=0x71ff90, len=384, ch=0x72bfc0, stereo=0) at mixasm.c:2022
#2 0x00007ffff5d55ba8 in putchn (chn=0x72bfc0, len=384, opt=0) at mix.c:129
#3 0x00007ffff5d55f14 in mixMixChanSamples (ch=0x7fffffffcc00, n=1, s=0x7ffff5d3fcc0, len=384, rate=22050, opt=0) at mix.c:180
#4 0x00007ffff405f312 in getchansample (this=0x7ffff4268a80, ch=9, buf=0x7ffff5d3fcc0, len=384, rate=22050, opt=0) at itplay.c:1817
#5 0x00007ffff4061fcd in itpGetLChanSample (ch=9, buf=0x7ffff5d3fcc0, len=384, rate=22050, opt=0) at itpplay.c:534
#6 0x00007ffff599375a in plDrawScopes () at cpiscope.c:365
#7 0x00007ffff5993fd0 in scoDraw () at cpiscope.c:464
#8 0x00007ffff598add2 in plmpDrawScreen () at cpiface.c:772
#9 0x00007ffff598ae30 in plmpCallBack () at cpiface.c:789
#10 0x00007ffff697be9e in _fsMain (argc=2, argv=0x7fffffffd088) at pfsmain.c:266
#11 0x00007ffff7dcc332 in init_modules (argc=2, argv=0x7fffffffd088) at pmain.c:207
#12 0x00007ffff7dcc472 in _bootup (argc=2, argv=0x7fffffffd088) at pmain.c:237
#13 0x00000000004022e0 in runocp (handle=0x6040d0, argc=2, argv=0x7fffffffd088) at kickload.c:518
#14 0x000000000040243a in main (argc=2, argv=0x7fffffffd088) at kickload.c:568

[Chuck Anderson]

Post by Jan Kratochvil

Post by Chuck Anderson
I'm trying to debug an issue for the upstream author of ocp and am
running into an issue where gdb is showing "<value optimized out>" for
variables even though I've compiled the program with gcc -g -O0.

[...]

Post by Chuck Anderson
gcc -g -O0 -fPIC -Wall -I.././ -I.././gnulib kickload.c -o kickload.o -c
gcc -g -O0 -fPIC -Wall -I.././ -I.././gnulib compdate.c -o compdate.o -c
...
gcc -g -O0 -fPIC -Wall -I./ -I./gnulib -o ocp boot/kickload.o -pthread -ldl goodies/helpc/ocphhc doc/opencp.dox ocp.hlp

gcc -g -O0 -fpic -Wall -I.././ -O mixasm.c -o mixasm.o -c
as there is explicit -O in dev/Makefile there. After removing it getting
a valid dump with no <value optimized out>.
For the -O build found one <value optimized out> as correct and one <value
optimized out> as some bug in either gdb or gcc but that is out of the scope
of this mail thread. -O0 -g works, NOTABUG.

Thanks a bunch for this!