Re: [musl] add loongarch64 port v7.

[Szabolcs Nagy <nsz@port70.net>]

* 王洪亮 <wanghongliang@loongson.cn> [2023-04-18 09:28:49 +0800]:
> +++ b/arch/loongarch64/bits/signal.h
> @@ -6,14 +6,27 @@
>  #define SIGSTKSZ    16384
>  #endif
> 
> +#if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
>  typedef unsigned long greg_t, gregset_t[32];
> 
> -typedef struct sigcontext {
> +struct sigcontext {
>      unsigned long sc_pc;
> -    gregset_t     sc_regs;
> -    unsigned int  sc_flags;
> -    unsigned long sc_extcontext[];
> +    unsigned long sc_regs[32];
> +    unsigned int sc_flags;
> +    unsigned long sc_extcontext[] __attribute__((__aligned__(16)));
> +};

this looks good. (i don't know if this is really
needed in signal.h, but other targets have it too)

> +
> +typedef struct {
> +    unsigned long __pc;
> +    unsigned long __gregs[32];
> +    unsigned int __flags;
> +    unsigned long __extcontext[] __attribute__((__aligned__(16)));
>  } mcontext_t;

i would use the same struct tag as glibc so

typedef struct mcontext_t { ...

(we don't need c++ abi compat with glibc, but
it's nicer to be consistent)

> +#else
> +typedef struct {
> +    unsigned long __space[34];
> +} mcontext_t;

i would add the aligned attribute here.

(it's more important to match the kernel layout than to
avoid c extensions in standard mode: loongarch c compilers
will all support the aligned attribute in system headers)

> +#endif
> 
>  struct sigaltstack {
>      void   *ss_sp;
> @@ -23,11 +36,10 @@ struct sigaltstack {
> 
>  typedef struct __ucontext
>  {
> -    unsigned long      uc_flags;
> +    unsigned long      __uc_flags;
>      struct __ucontext  *uc_link;
>      stack_t            uc_stack;
>      sigset_t           uc_sigmask;
> -    long               __uc_pad;
>      mcontext_t         uc_mcontext;
>  } ucontext_t;

looks good.

(the only issue is if some code uses uc_flags in an
arch independent way. i don't know if there is any
use for it on linux. but we can fix that later on
both glibc and musl side if it comes up.)