My c code on compiling on gcc is giving the error Cannot find entry symbol _start defaulting to 00000. Can anyone tell me why and how to correct it?
The command line is arm-none-eabi-gcc -O3 -march=armv7-a -mtune=cortex-a8 -mfpu=neon -ftree-vectorize -mfloat-abi=softfp file path and the target platform is a-8 sitara cortex processor.
The only reason the compiler threw the above error is because the start code(_start function) generated by the OS for running your code cannot find the default or registered function main. So either you can use _start function instead of main function but the compilation command should be gcc -nostartfiles filename.c but using _start there are a lot of exceptions so better to use main instead.
the -none- part means that your toolchain doesn't build for a particular operating system, so you must define a _start entry point. For non-bare-metal toolchains that build for a particular operating system, _start is provided by the standard library that in order will call main when everything is set up.
Related
I'm trying to port a project from Cortex M0 to Cortex M4 with hardware floating point extension, the new target soc is nRF52832.
The error I am getting from the linker is the following
arm-unknown-eabi/bin/ld: error: x.o uses VFP register arguments, firmware does not
where firmware is the name of the output file fro the linker.
This is an issue with the arm ABI for floating point, I want to use the FPU as it is requested by
the FreeRTOS port I want to use but I don't get how to tweak my linker flags to make it possible.
This is the set of linker flags I'm currently using
-L/path/to/nrfx/mdk
-Wl, --no-undefined
-Wl,--as-needed -march=armv7e-m+fp -mthumb -mfloat-abi=hard -mabi=aapcs
-Wl, --start-group support/libs/libQRCode.a support/libs/libSPIFFS.a
-Wl, --no-undefined
-Wl, --as-needed
-Wl, --gc-sections --specs=nosys.specs -T/path/to/linker_script.ld /toolchain/path/to/lib/libm.a
-Wl, --end-group
The -mfloat-abi flag is a compiler-only flag, so there is no point in passing it to the linker.
In order to be able to build a firmware image that uses the hard-float ABI, all object files passed to the linker must be compiled to use that ABI. You issue is most likely due to the fact that you are passing to the linker one or more object files compiled with the soft-float ABI instead; for example, the /toolchain/path/to/lib/libm.a file path in your linker command line looks suspicious, you should use the hard-float version of libm.a, which you will likely find in the hard/ sub-folder of your toolchain library path.
I'm using the Windows version of Clang (LLVM) 8 under Windows.
I'm compiling a code which uses OpenMP.
Under the lib folder of Clang there are 2 files which are OpenMP related:
libomp.lib.
libiomp5md.dll.
My questions are:
When I compile the code I use the flags -Xclang -fopenmp for the compiler. In in GCC and ICC using the flags tell the compiler to link the OpenMP library automatically. What about Clang? Does it do it automatically or must I link with libomp.lib manually? Is there a way to trigger automatic linking to the OpenMP library?
Answer: This was answered in Michael Klemm's answer below - Use the clang driver both for compiling and linking and then the -fopenmp will work as in GCC.
When I link with libomp.lib manually (Defining as a library for the linker) the output exe requires libomp.dll while the supplied OpenMP Dynamic Library is libiomp5md.dll. Is that a bug or is it because I link manually?
Answer: The libomp.dll is supplied in the bin folder and not the lib folder.
What's the proper way to utilize OpenMP in Clang under Windows? The clang-cl driver doesn't work with /openmp or -openmp as the MSVC's cl compiler.
Answer: Currently it can be done either with clang -fopenmp ..., clang-cl -Xclang -fopenmp ... or clang-cl /clang:-fopenmp ... (Which is equivalent of -Xclang -fopenmp).
Remark
On Windows I use Windows Driver of Clang using clang-cl.
Adding clarity to what the OpenMP libraries actually are, and how to use them on Windows with clang-cl
libomp.dll and libiomp5md.dll ARE THE SAME FILES!
When compiling for Windows, you link against libomp.lib OR libiomp5md.lib which will link to the same-named DLL at runtime, i.e. libomp.dll OR libiomp5md.dll respectively.
If you load 2 files that use the "different-name DLL," the interpreter will crash and give you a nasty error like: OMP: Error #15: Initializing libiomp5md.dll, but found libomp.dll already initialized.
Why? Because the program has no idea they are the same DLL, they have different names, so it assumes they are different. And it crashes. For this reason only, you can choose to swap which OpenMP DLL you link to in your program.
If your program doesn't crash and give you an error, you can keep using the same link to OpenMP. Otherwise, to silence the error, link to the one that is loaded by another program already.
If using clang-cl.exe which is the "drop-in" Clang replacement for MSVC cl.exe you should pass a compiler argument such as -Xclang -fopenmp which will convert the argument over to "Clang language." Don't forget to still pass to the linker the OpenMP LIB you chose, because on Windows, it won't be automatic.
That's all I've learned as brief as possible about OpenMP linking on Windows.
To compile and link OpenMP code with clang on Windows, you will have to pass -fopenmp to both the compiler and the linker:
clang -fopenmp -o bla.obj -c bla.c
clang -fopenmp -o bla.exe bla.obj
I am trying to compile an AVR32 program with GCC 3.4.2 and getting the following linker warning:
input is not relaxable
Could someone explain what that warning means?
Linker flags: -Wl,--start-group -Wl,--end-group -Wl,--gc-sections -mpart=uc3c0512c -Wl,--relax -Wl,-e,_trampoline
From Atmel
Linker relaxing is enabled in the linker by passing the ‘—relax’
option to the linker. If using GCC as a frontend for the linker, this
option is automatically passed to the linker when using ‘-O2’ or
‘-O3’ or explicitly using the ‘-mrelax’ option. Marking the output
objects from GCC as relaxable is done by giving the assembler the
‘--linkrelax’ option. This option is automatically passed on to the
assembler from GCC when using ‘-O2’ or ‘-O3’ or explicitly using the
‘-mrelax’ option.
Perhaps you didn't pass the needed options to the assembler for the --relax option to work in the linker.
I need an help!! I am trying to build a standalone executable ie without ANY dynamic linking.
I wrote a small test program, generated a relocatable object file for it called test.o. When I try to build the standalone executable using GNU linker I get the below error:
$ld -static -o test test.o /usr/lib/crt1.o /usr/lib/crti.o /usr/lib/libc.a /usr/lib/gcc/i486-linux-gnu/4.4/libgcc.a /usr/lib/gcc/i486-linux-gnu/4.4/libgcc_eh.a
/usr/lib/gcc/i486-linux-gnu/4.4/libgcc_eh.a(unwind-dw2-fde-glibc.o): In function _Unwind_Find_FDE':
(.text+0x190b): undefined reference todl_iterate_phdr'
How to resolve the undefined symbol dl_iterate_phdr. In which archive this symbol is present?
Thanks!!!
EDIT1:
Just in case if I am not very clear, my motive is to generate a standalone executable ie an executable which is completely ready for execution while it gets loaded into memory i.e.) all symbol resolution and relocation is done by program linker itself instead of dynamic linker. Is it possible to generate such an executable?
FINAL UPDATE:
Now I got it to get complied with ld directly using the below command:
$ld -static -o test /usr/lib/crt1.o /usr/lib/crti.o /usr/lib/gcc/i486-linux-gnu/4.4.3/crtbeginT.o /usr/lib/gcc/i486-linux-gnu/4.4.3/crtend.o test.o --start-group /usr/lib/gcc/i486-linux-gnu/4.4.3/libgcc.a /usr/lib/gcc/i486-linux-gnu/4.4.3/libgcc_eh.a /usr/lib/libc.a --end-group
man ld says --start-group archives --endgroup is used to resolve circular references!! Also i find symbol dl_iterate_phdr is defined in libc.a.
Thanks all for your help!!
When I try to build the standalone executable using GNU linker
Don't. Use of ld to link any user-space program is most often a bug. Your link line is certainly incorrect.
Use compiler driver to do the heavy lifting for you. This should work:
gcc -static -o test test.o
I am looking to use ld since I wanted to build a standalone executable
What makes you believe that GCC-built executable is less stand-alone than ld-built one? Whatever it is, you are mistaken: gcc simply invokes ld with correct arguments.
If you're getting this error when targeting android, you need to link against libdl.so (-ldl)
gcc -o main main.c -L . -static-libgcc -Wl,-static -lhello -lc
I am compiling a C file using the gcc flag -ffunction-sections, to move every function into it's own section. The assembler is throwing the error:
job_queue.s:2395: Error: operation combines symbols in different segments
The compiler's assembly output at line 2395 is given here:
.section .debug_ranges,info
.Ldebug_ranges0:
.4byte .LBB7-.Ltext0
The symbol LBB7 is in the function (and thus the section) named ".text.add_event_handler"
The symbol Ltext0 is in the (otherwise empty) section named: ".text"
GCC --version gives:
pic30-elf-gcc.exe (GCC) 4.0.3 (dsPIC30, Microchip v3_30) (B) Build date: Jun 29 2011
If I use the compiler flag -g0 (to turn off debug info) everything compiles and runs perfectly.
My question:
Is this GCC output clearly wrong? It seems to me that GCC should have calculated the symbol LBB7's offset from the beginning of the .add_even_handler section instead of the .text section.
I suspect I am misunderstanding something because I cannot find anyone having the same difficulty on the Google.
The GCC output is definitely wrong. Perhaps it's fixed in newer GCC versions. If you can't upgrade you compiler, try compiling with -gdwarf-2 or, failing that, with -gdwarf-2 -gstrict-dwarf (for -gstrict-dwarf you'll have to upgrade the compiler too).
What this option does is to instruct GCC to generate (strict) DWARF2, which does not include non-contiguous address ranges support, introduced in DWARF3.
Of course, this may degrade the debugging information quality somewhat, YMMV.