gcc 4.8.2 no recognized debugging information - linux

I have two workstations, one of them runs Debian Wheezy and has gcc 4.9.2
Second one runs RHEL 5.5, gcc version is 4.8.2
when I compile the same code with the same options:
$gcc -O3 -DNDEBUG -g -o test test.c
I get all the necessary debugging information on gcc 4.9 on Debian box, however on RHEL box objdump says:
$ objdump --debugging test
test: file format elf64-x86-64
objdump: test: no recognized debugging information
What do I do wrong?

From looking around, this appears to be a known bug or limitation in objdump:
https://bugzilla.redhat.com/show_bug.cgi?id=118383
https://sourceware.org/bugzilla/show_bug.cgi?id=6483
How can I tell if a library was compiled with -g?
Suggested workarounds are using objdump -W, readelf -w, or gcc -gstabs.

Related

How do I link libraries from multiple locations (corresponding to multiple GCC versions)?

I am currently trying to use Oracle Linux 6 OS on a SPARC S7 server to run the NPB benchmarks (with OpenMP multithreading support). The OS comes preloaded with gcc 4.4.7, which is missing the Niagara 7 optimizations. I downloaded devtoolset-3 from the Oracle Yum Repository, which has gcc 4.9.2 installed in /opt/rh/devtoolset-3/root/usr/bin. However, when I compile the NPB benchmark using the newer gcc, it automatically links to libraries associated with the older gcc 4.4.7 (located in /usr/lib). This caused my program to segfault during execution. I believe that it is because libgomp 4.4.7 is incompatible with libgomp 4.9.2. I have tried several ways of linking to the libraries in the gcc 4.9.2 folder (which is /opt/rh/devtoolset-3/root/usr/lib/gcc); none of the methods work:
-Xlinker -rpath=lib_location
-Wl -Bstatic
-L lib_location
The closest I got was when using -Wl -Bstatic ~/libgomp.a or -static -L ~/libgomp.a. It fails to find libraries such as libm that reside in the default gcc lib folder (usr/lib).
The actual command used to link is:
/opt/rh/devtoolset-3/root/usr/bin/gcc -O3 -fopenmp -mcmodel=medmid -static -L/opt/rh/devtoolset-3/root/usr/lib/gcc/sparc64-redhat-linux/4.9.2 -o ../bin/bt.W.x bt.o initialize.o exact_solution.o exact_rhs.o set_constants.o adi.o rhs.o x_solve.o y_solve.o solve_subs.o z_solve.o add.o error.o verify.o ../common/print_results.o ../common/c_timers.o ../common/wtime.o -lm -L/opt/rh/devtoolset-3/root/usr/lib/gcc/sparc64-redhat-linux/4.9.2/lib/
/opt/rh/devtoolset-3/root/usr/libexec/gcc/sparc64-redhat-linux/4.9.2/ld: cannot find -lm
/opt/rh/devtoolset-3/root/usr/libexec/gcc/sparc64-redhat-linux/4.9.2/ld: cannot find -lrt
/opt/rh/devtoolset-3/root/usr/libexec/gcc/sparc64-redhat-linux/4.9.2/ld: cannot find -lpthread
/opt/rh/devtoolset-3/root/usr/libexec/gcc/sparc64-redhat-linux/4.9.2/ld: cannot find -lc
Is there a way I can link just the libgomp library from gcc 4.9.2 while linking the remaining libraries from gcc 4.4.7?
The devtoolset compilers are all using the system libgcc, libstdc++, version 4.4.7, and can therefore not compile e.g. c++11.
I guess the gcc53-c++-5.3.0-1.el6.x86_64.rpm will do. Comes with the internal */gcc53/lib64{libgcc_s.so**, libgomp.so**, libstdc++} (version 5.3.0) ... Provides /usr/bin/{ gcc53, g++53 }
The package was created a year ago ... well tested, as extra compiler. Download link : https://drive.google.com/file/d/0B7S255p3kFXNbTBneHgwSzBodFE/view?usp=sharing
If you're going to do the -Wl,-Bstatic thing, make sure to follow it immediately by -Wl,-Bdynamic to reset to normal after your added library argument. By default, not all system libraries have static versions installed, which is why you get e.g. cannot find -lc.
So you can try this as a modification of your workaround:
-Wl,-Bstatic ~/libgomp.a -Wl,-Bdynamic
Not pretty, and this question deserves a much better answer (this is still pretty much a hack), but it should get the job done for now.

Compiling program with Open Source libFTDI

I use Asus router (based on ARMv7 proc) with Advanced Tomato installed
on it as my ARMv7 developer platform. I install compiler (gcc - 5.4.0-1)
plus dependencies and libFTDI (libftdi1 - 1.3-1) from OpenWRT Linux
repo. OpenWRT does not provide libftdi-dev so I copied ftdi.h file from libFTDI download page to /opt/include directly. I try to compile program taken directly from libFTDI samples. The
compiler command is:
gcc -v -Wl,-rpath=/opt/usr/local/lib -Wl,--dynamic-linker=/opt/lib/ld-linux.so.3 -L/opt/lib -O2 -pipe -march=armv7-a -mtune=cortex-a9-fno-caller-saves -mfloat-abi=soft -l ftdi1 d.c -o d
But compilation fails because:
/opt/bin/ld: cannot find -lftdi1
But there is /opt/usr/local/lib/libftdi1.so linked to libftdi1.so.2
My LD_LIBRARY_PATH looks like this:
/lib:/usr/lib:/usr/local/lib:/opt/lib:/opt/usr/lib:/opt/include:/opt/usr/local/lib:/opt/usr/include
So what the problem is?
I dont know why (probably bug) but for compiler taken from OpenWRT repo, MUST have wanted library in /opt/lib. So simply copy libftdi1.so.2.3.0 file and linking it to libftdi1.so resolved problem. That means that it does not use correctly LD_LIBRARY_PATH variable. Finally compilation command looks like this:
gcc -v -Wl,-rpath=/opt/usr/local/lib -Wl,--dynamic-linker=/opt/lib/ld-linux.so.3 -L/opt/lib -O2 -pipe -march=armv7-a -mtune=cortex-a9 -fno-caller-saves -mfloat-abi=soft -l ftdi1 arco.c -o arco
From my point of view - topic closed

clang++ as drop-in g++ replacement

I'm trying to use clang++ as drop-in replacement for G++. I'm compiling for AArch64, but for linking, clang seems to invoke the native (x86) /usr/bin/ld instead of that from AArch64 GCC suite. The clang command line looks like:
clang++ -target aarch64-linux-gnu -v \
-gcc-toolchain /path/to/aarch64/gcc \
--sysroot=/path/to/aarch64/gcc/aarch64-linux-gnu/libc \
<some other options> <obj files>
And from the verbose output, I get:
Ubuntu clang version 3.4-1ubuntu3 (tags/RELEASE_34/final) (based on LLVM 3.4)
Target: aarch64--linux-gnu
Thread model: posix
Found candidate GCC installation: /path/to/aarch64/gcc/lib/gcc/aarch64-linux-gnu/4.9.3
Selected GCC installation: /path/to/aarch64/gcc/lib/gcc/aarch64-linux-gnu/4.9.3
"/usr/bin/ld" --sysroot=/path/to/aarch64/gcc/aarch64-linux-gnu/libc ...
I don't get why clang got around choosing the native linker. The link fails for obvious reasons that object files are AArch64 ELF. Compilation lines similar to the above, but they go OK.
Any thoughts?
PS: I'm a novice clang user
I managed to find a solution: GCC accepts -B option to point to the search path where it'd try to locate the utilities. It turns out--although not documented--that clang too accepts this option. For me, having -B point to AArch64 binutils solved the problem. Another suggestion was to add the AArch64 binutils in $PATH.

g++ throwing file not recognized: File format not recognized error

getting following error with the command g++ -o test -L . -l pq
libpq.so: file not recognized: File format not recognized
#file libpq.so
libpq.so: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), not stripped
gcc version 4.1.2 20070115 (SUSE Linux)
I am getting the same error if I try to use -l dbodbc instead of -l pq.
Note that test.c is a simple hello world program.
Thanks in Advance.
file /usr/bin/g++ tells you that g++ itself is a 64-bit executable, i.e. it runs on a 64-bit machine, it doesn't tell you that g++ can compile 64-bit code (it's very unlikely but it could be a cross compiler for a completely different processor!) Use g++ -v or g++ -dumpmachine to find out what target it generates executables for.
G++ doesn't actually use that library, it just passes the -l option to the linker, so the error is coming from the linker, ld
If ld and objdump are both saying they can't recognize the library but the same file is fine on a different machine, I would try updating or reinstalling the binutils package, which provides both ld and objdump.
You might have a 32-bit binutils installed, so its ld and objdump wouldn't understand the x86_64 library. Ensure you have the 64-bit (i.e. x86_64) binutils RPM installed.

Placement of `-l' option in gcc

I have some trouble with the placement of the -l option when using gcc. Here's a stripped down version for reproduce the problem.
t.c:
#include <pthread.h>
int main() {
pthread_create(0, 0, 0, 0);
}
and in terminal:
$ gcc -lpthread t.c
/tmp/ccmkwV7B.o: In function `main':
t.c:(.text+0x29): undefined reference to `pthread_create'
collect2: ld returned 1 exit status
$ gcc t.c -lpthread
$ (compiles ok)
Why do I have to put -lpthread in the end to make it work? And it seems that this problem only occurs on 32bit linux.
My environment info is attached below:
gcc -lpthread t.c fails on this machine.
$ gcc --version
gcc (Ubuntu/Linaro 4.6.1-9ubuntu3) 4.6.1
$ uname -rm
3.0.0-12-generic i686
gcc -lpthread t.c works on this machine.
$ uname -rm
2.6.18-274.3.1.el5 x86_64
$ gcc --version
gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-51)
I looked up the gcc manual, and it says that "the placement of -l is significant". What exactly does it mean?
From the manual,
It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified. Thus, foo.o -lz bar.o searches library z after file foo.o but before bar.o. If bar.o refers to functions in z, those functions may not be loaded.
This means it is very interesting that linking the library first works on gcc 4.1.2. This might have to do with the default libraries linked to by the compiler. I know on some installations I don't need to explicitly link to pthreads.
On further reflection, I think the issue is with the flag --as-needed, which may be on by default in your gcc 4.6 system. See this link for some discussion.

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