Re: [Qemu-devel] tcg_register_jit_int() interface problem

[Laurent Vivier]

Le 16/07/2018 à 13:10, Aleksandar Markovic a écrit :
> Hello, all.
> 
> 
> Just a little background:
> 
> 
> One of the fields in an ELF header is e_machine. It is meant to contain
> "machine architecture". The numerical value is approved by a committee.
> Some values for common targets are: EM_PPC, EM_PPC64, EM_ARM,
> EM_AARCH64, etc.
> 
> 
> The TCG function tcg_register_jit_int() expects that the preprocessor
> constant ELF_HOST_MACHINE is defined, and uses internally the value of
> that constant.
> 
> 
> Consider, let's say, ARM: It definesELF_HOST_MACHINE in
> tcg/arm/tcg-target.inc.c as
> 
> 
> #define ELF_HOST_MACHINE EM_ARM
> 
> 
> while in tcg/aarch64/tcg-target.inc.c it defines it as
> 
> 
> #define ELF_HOST_MACHINE EM_AARCH64
> 
> 
> For MIPS, the situation is different: Up until recently, MIPS had only
> one value for e_machine: that was EM_MIPS (used for both 32-bit and
> 64-bit MIPS systems). However, new nanoMIPS systems have a new value in
> that field: EM_NANOMIPS (that is to be applied for both 32-bit and
> 64-bit nanoMIPS systems).
> 
> 
> The situation described above represent a problem for us developing
> nanoMIPS support, forcing us to have different compilations (and
> executables) for MIPS and nanoMIPS.
> 
> 
> Is there a possibility to refactor tcg_register_jit_int() to receive
> "e_machine" value as an argument, instead of expecting preprocessor
> constant to be set?

I don't know this par of code, but for PPC we have:

#if TCG_TARGET_REG_BITS == 64
# define ELF_HOST_MACHINE EM_PPC64
#else
# define ELF_HOST_MACHINE EM_PPC
#endif

So perhaps you could have something like:

#if defined(HOST_NANOMIPS)
# define ELF_HOST_MACHINE EM_NANOMIPS
#else
# define ELF_HOST_MACHINE EM_MIPS
#endif

Thanks,
Laurent