Question about gcc option -mcmodel

[Ramana Radhakrishnan]

On 01/08/2018 03:56, xiebin (F) wrote:
> Hi everyone,
> I was compiling a HPC application named NorESM on ARM64 machine with GCC7.3.
> I met "relocation truncated to fit" error, so I added "-mcmodel=large" and successfully built the project. However, the executable seems not executable.
> [xie@sms bld]$ strace ./cesm.exe
> execve("./cesm.exe", ["./cesm.exe"], [/* 64 vars */]) = -1 ENOMEM (Cannot allocate memory)
> --- SIGSEGV {si_signo=SIGSEGV, si_code=SI_KERNEL, si_addr=0} ---
> +++ killed by SIGSEGV +++
> Segmentation fault (core dumped)
> I found this in GCC manual aarch64 section:
>        -mcmodel=small
>            Generate code for the small code model.  The program and its statically defined symbols must be within 4GB of each other.  Programs can be statically or
>            dynamically linked.  This is the default code model.
> 
>        -mcmodel=large
>            Generate code for the large code model.  This makes no assumptions about addresses and sizes of sections.  Programs can be statically linked only.

I don't think we ever got everything working for building shared objects
with -mcmodel=large fully implemented.

Applications should be able to interoperate with executables built with
-mcmodel=large and libraries built with -mcmodel=small.

Can you debug this in gdb and see why you get the SEGV ?


regards
Ramana

> 
> I also compiled the project on x86-64 with intel compiler. In this situation, I added "-mcmodel=medium" and compilation and execution are successful. Below is its explanation:
>        -mcmodel=mem_model (L*X only)
> 
>               Tells the compiler to use a specific memory model to generate code and store data.
> 
>               Architecture Restrictions: Only available on Intel(R) 64 architecture
> 
>               Arguments:
> 
>               mem_model         Is the memory model to use. Possible values are:
> 
>                                 small          Tells the compiler to restrict code and data to the first 2GB of address space. All accesses of code and  data  can  be
>                                                done with Instruction Pointer (IP)-relative addressing.
> 
>                                 medium         Tells  the compiler to restrict code to the first 2GB; it places no memory restriction on data. Accesses of code can be
>                                                done with IP-relative addressing, but accesses of data must be done with absolute addressing.
> 
>                                 large          Places no memory restriction on code or data. All accesses of code and data must be done with absolute addressing.
> 
>               Default:
> 
>               -mcmodel=small    On systems using Intel(R) 64 architecture, the compiler restricts code and data to the first 2GB of address space. Instruction Pointer
>                                 (IP)-relative addressing can be used to access code and data.
> 
> Here are my questions:
> 
> 1.       What does "Programs can be statically linked only" means? Does it mean I must compile all dependency libraries staticly? What about the basic librarie like libc and libgcc?
> 
> 2.       Does GCC has similar option to separate code and data like Intel Compiler does?
>