Re: [PATCH] linux-user: Add AT_EXECFN and AT_EXECFD auxval

[Laurent Vivier <laurent@vivier.eu>]

Le 21/02/2020 à 21:28, Lirong Yuan a écrit :
> This change adds the support for AT_EXECFN and AT_EXECFD auxval.

Why do we need AT_EXECFD?

AT_EXECFD is normally only used with binfmt_misc so I don't see any use
cases for it with QEMU.

For AT_EXECFN, according to kernel commit

  651910874633 execve filename: document and export via auxiliary vector

It sould be like readlink("/proc/self/exe",), and thus I think we should
use realpath() like we have in syscall.c for TARGET_NR_readlink:

 8843     case TARGET_NR_readlink:
...
 8854                 char real[PATH_MAX], *temp;
 8855                 temp = realpath(exec_path, real);
...

Thanks,
Laurent

> 
> Signed-off-by: Lirong Yuan <yuanzi@google.com>
> ---
>  linux-user/elfload.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/linux-user/elfload.c b/linux-user/elfload.c
> index f3080a1635..7e0f3042f1 100644
> --- a/linux-user/elfload.c
> +++ b/linux-user/elfload.c
> @@ -1568,7 +1568,7 @@ struct exec
>                                   ~(abi_ulong)(TARGET_ELF_EXEC_PAGESIZE-1))
>  #define TARGET_ELF_PAGEOFFSET(_v) ((_v) & (TARGET_ELF_EXEC_PAGESIZE-1))
>  
> -#define DLINFO_ITEMS 15
> +#define DLINFO_ITEMS 17
>  
>  static inline void memcpy_fromfs(void * to, const void * from, unsigned long n)
>  {
> @@ -1888,11 +1888,14 @@ static abi_ulong loader_build_fdpic_loadmap(struct image_info *info, abi_ulong s
>      return sp;
>  }
>  
> -static abi_ulong create_elf_tables(abi_ulong p, int argc, int envc,
> +static abi_ulong create_elf_tables(struct linux_binprm *bprm,
>                                     struct elfhdr *exec,
>                                     struct image_info *info,
>                                     struct image_info *interp_info)
>  {
> +    abi_ulong p = bprm->p;
> +    int argc = bprm->argc;
> +    int envc = bprm->envc;
>      abi_ulong sp;
>      abi_ulong u_argc, u_argv, u_envp, u_auxv;
>      int size;
> @@ -2032,6 +2035,8 @@ static abi_ulong create_elf_tables(abi_ulong p, int argc, int envc,
>      NEW_AUX_ENT(AT_CLKTCK, (abi_ulong) sysconf(_SC_CLK_TCK));
>      NEW_AUX_ENT(AT_RANDOM, (abi_ulong) u_rand_bytes);
>      NEW_AUX_ENT(AT_SECURE, (abi_ulong) qemu_getauxval(AT_SECURE));
> +    NEW_AUX_ENT(AT_EXECFN, info->file_string);
> +    NEW_AUX_ENT(AT_EXECFD, bprm->fd);
>  
>  #ifdef ELF_HWCAP2
>      NEW_AUX_ENT(AT_HWCAP2, (abi_ulong) ELF_HWCAP2);
> @@ -2870,8 +2875,8 @@ int load_elf_binary(struct linux_binprm *bprm, struct image_info *info)
>  #endif
>      }
>  
> -    bprm->p = create_elf_tables(bprm->p, bprm->argc, bprm->envc, &elf_ex,
> -                                info, (elf_interpreter ? &interp_info : NULL));
> +    bprm->p = create_elf_tables(bprm, &elf_ex, info,
> +                                (elf_interpreter ? &interp_info : NULL));
>      info->start_stack = bprm->p;
>  
>      /* If we have an interpreter, set that as the program's entry point.
>