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Re: [PATCH] linux-user: Use getcwd syscall directly


From: Laurent Vivier
Subject: Re: [PATCH] linux-user: Use getcwd syscall directly
Date: Fri, 24 Jul 2020 15:52:59 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0

Le 23/07/2020 à 12:27, Andreas Schwab a écrit :
> The glibc getcwd function returns different errors than the getcwd
> syscall, which triggers an assertion failure in the glibc getcwd function
> when running under the emulation.
> 
> Signed-off-by: Andreas Schwab <schwab@suse.de>
> ---
>  linux-user/syscall.c | 9 +--------
>  1 file changed, 1 insertion(+), 8 deletions(-)
> 
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index b9144b18fc..e4e46867e8 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -388,14 +388,7 @@ static bitmask_transtbl fcntl_flags_tbl[] = {
>    { 0, 0, 0, 0 }
>  };
>  
> -static int sys_getcwd1(char *buf, size_t size)
> -{
> -  if (getcwd(buf, size) == NULL) {
> -      /* getcwd() sets errno */
> -      return (-1);
> -  }
> -  return strlen(buf)+1;
> -}
> +_syscall2(int, sys_getcwd1, char *, buf, size_t, size)
>  
>  #ifdef TARGET_NR_utimensat
>  #if defined(__NR_utimensat)
> 

Reviewed-by: Laurent Vivier <laurent@vivier.eu>

I'll add in the commit message the explanation you did on your previous
attempt:

"When the syscall returns ENAMETOOLONG,
the glibc wrapper uses a fallback implementation that potentially
handles an unlimited path length, and returns with ERANGE if the
provided buffer is too small.  The qemu emulation cannot distinguish the
two cases, and thus always returns ERANGE.  This is unexpected by the
glibc wrapper."

Thanks,
Laurent



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