[MacPorts] #48284: gdb 7.9.1 cannot determine type of primitive global variables
MacPorts
noreply at macports.org
Tue Jul 7 16:39:31 PDT 2015
#48284: gdb 7.9.1 cannot determine type of primitive global variables
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Reporter: rbd@… | Owner: macports-
Type: defect | tickets@…
Priority: Normal | Status: new
Component: ports | Milestone:
Keywords: global variable types unknown | Version: 2.3.3
| Port: gdb
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Hi all,
I am having problems with gdb being unable to recognize the type of
primitive global variables within an executable compiled from multiple
source files under MacOS Yosemite 10.10.4 and Xcode 6.4 (6E35b). The same
problem occurs whether I compile with either /usr/bin/cc or /usr/bin/gcc,
both of which appear to be using Apple LLVM version 6.1.0 (clang-602.0.53)
based on LLVM 3.6.0svn. (I have not tried with a self-built gcc compiled
from gcc source.) I first noticed this a few days ago after a MacPorts
update which installed gdb 7.9.1, but the same problem occurred when I
deactivated MacPorts gdb 7.9.1 and reverted to MacPorts gdb 7.7.1. I also
tried building gdb 7.7.1 from GNU source and still get the same problem.
(Curiously, I am fairly sure that this problem did not exist with MacPorts
gdb 7.7.1 before I upgraded Xcode from 6.3 to 6.4, but I upgraded gdb at
the same time from 7.7.1 to 7.9.1 and so cannot be certain of exactly what
triggered this bug.)
This problem is *not* exhibited by the current MacPorts gdb-apple port,
but since (i) gdb-apple is based on a relatively old gdb revision (6.3)
and thus possibly of questionable future lifespan, and (ii) it seems
pointless to have a 'standard' (i.e., 7.9.1) gdb port that does not work,
I am very ardently hoping that this issue will be addressed in the gdb
7.9.1 port.
You can reproduce this bug by creating the following two files m0.c and
m1.c:
% cat m0.c[[BR]]
#include <stdio.h>[[BR]]
float gf;[[BR]]
extern void func();[[BR]]
int main() {
gf= 1.23;[[BR]]
printf("gf: %4.2f\n", gf);[[BR]]
func();[[BR]]
}[[BR]]
% cat m1.c[[BR]]
#include <stdio.h>[[BR]]
extern float gf;[[BR]]
void func() {
float lf;[[BR]]
lf= 4.56;[[BR]]
printf("lf: %4.2f\n", lf);[[BR]]
}[[BR]]
Then compile as follows:
% cc -g -c m0.c -o m0.o[[BR]]
% cc -g -c m1.c -o m1.o[[BR]]
% cc -g -o m m0.o m1.o
When you debug with MacPorts gdb 7.9.1, the type of the global float gf is
unknown to gdb from within main():
% ggdb m[[BR]]
GNU gdb (GDB) 7.9.1[[BR]]
...[[BR]]
This GDB was configured as "x86_64-apple-darwin14.3.0".[[BR]]
...[[BR]]
Reading symbols from m...done.[[BR]]
(gdb) break main[[BR]]
Breakpoint 1 at 0x100000eee: file m0.c, line 5.[[BR]]
(gdb) break func[[BR]]
Breakpoint 2 at 0x100000f27: file m1.c, line 5.[[BR]]
(gdb) run[[BR]]
Starting program: /private/tmp/m[[BR]]
warning:
`/BinaryCache/coreTLS/coreTLS-35.30.2~2/Objects/coretls.build/coretls.build
/Objects-normal/x86_64/system_coretls_vers.o': can't open to read symbols:
No such file or directory.[[BR]]
warning: Could not open OSO archive file
"/BinaryCache/coreTLS/coreTLS-35.30.2~2/Symbols/BuiltProducts/libcoretls_ciphersuites.a"[[BR]]
warning: Could not open OSO archive file
"/BinaryCache/coreTLS/coreTLS-35.30.2~2/Symbols/BuiltProducts/libcoretls_handshake.a"[[BR]]
warning: Could not open OSO archive file
"/BinaryCache/coreTLS/coreTLS-35.30.2~2/Symbols/BuiltProducts/libcoretls_record.a"[[BR]]
warning: Could not open OSO archive file
"/BinaryCache/coreTLS/coreTLS-35.30.2~2/Symbols/BuiltProducts/libcoretls_stream_parser.a"[[BR]]
Breakpoint 1, main () at m0.c:5[[BR]]
5 gf= 1.23;[[BR]]
(gdb) s[[BR]]
6 printf("gf: %4.2f\n", gf);[[BR]]
(gdb) s[[BR]]
gf: 1.23[[BR]]
7 func();[[BR]]
(gdb) ptype gf[[BR]]
type = <data variable, no debug info>[[BR]]
(gdb) print gf[[BR]]
$1 = 1067282596
However, the type of local float lf within func is known:
(gdb) continue[[BR]]
Continuing.[[BR]]
Breakpoint 2, func () at m1.c:5[[BR]]
5 lf= 4.56;[[BR]]
(gdb) s[[BR]]
6 printf("lf: %4.2f\n", lf);[[BR]]
(gdb) s[[BR]]
lf: 4.56[[BR]]
7 }[[BR]]
(gdb) ptype lf[[BR]]
type = float[[BR]]
(gdb) print lf[[BR]]
$2 = 4.55999994
The type of the global float gf is also unknown to gdb from within func():
(gdb) ptype gf[[BR]]
type = <data variable, no debug info>[[BR]]
(gdb) print gf[[BR]]
$3 = 1067282596
If instead you combine the two files m[01].c into the single file s.c with
the contents
#include <stdio.h>[[BR]]
float gf;[[BR]]
int main() {
void func();[[BR]]
gf= 1.23;[[BR]]
printf("gf: %4.2f\n", gf);[[BR]]
func();
}
void func() {
float lf;[[BR]]
lf= 4.56;[[BR]]
printf("lf: %4.2f\n", lf);
}
and compile with
% cc -o s -g s.c
then gdb works perfectly well, recognizing the type of gf and correctly
printing its floating point value within either main() or func().
Naturally, the actual program I am having a problem with is much larger
and really needs to be in multiple files, but I think this example shows
the problem about as succinctly as possible. The problem is not limited to
float variables -- a global int variable shows the same problem of unknown
type.
I have noticed that when I compile the above single-file s.c code, a
directory s.dSYM is created. This is supposedly done when a dsymutil
symbol utility is implictly run by cc. I have read that dsymutil is *not*
run when the source files are separately compiled into .o files and the
latter are then linked with a separate command (as in my multi-file cc
command sequence shown above). Perhaps this has some bearing on the
problem?
Please note also all of the references in the gdb output above to the
various missing files "/BinaryCache/coreTLS/..." when gdb first starts the
executable. There is no /BinaryCache directory on my system, and as these
errors seem to be related to symbol issues I wonder if this is connected
to the global variable type recognition problem.
Thanks,
Roger Davis
--
Ticket URL: <https://trac.macports.org/ticket/48284>
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