Re: [libposix-development] [PATCH 2/2] x86_32: use 'int 0x80' for system calls to improve protability

[Henrique A. <hd...@gm...>]

 Thanks for the patch. However, do you need those for linux 2.4 ? If
you do, that would be a variant from the default implementation. I'll
explain variants when I define platform sets, but the point is that
the amount of variants should be kept to a minimum possible. For linux
2.6, vsyscall can always be set and is considered to be the default
way to do system calls (because it's faster in modern processors), so
a second implementation would be redundant. Also, I wasn't considering
supporting linux 2.4 in x86. If someone is willing to switch to
libposix to use a newer standard, then probably the person is also
willing to update to linux 2.6 ;-)

 So, if you DEFINITELY need x86 linux 2.4 support in libposix, please
resend the patch as a variant: create a subdirectory called "linux24"
in system/linux/x86_32 and runtime/linux/x86_32 and create a separate
cmake file to support the variant by redefining the necessary support
files.

2009/6/26 Kirill A. Shutemov <ki...@sh...>:
> Not every kernel provide __kernel_vsyscall. It's possible to add
> configuration option later.
>
> Signed-off-by: Kirill A. Shutemov <ki...@sh...>
> ---
>  runtime/linux/x86_32/architecture_init.c |   22 +---------------------
>  system/linux/x86_32/system_calls.S       |   17 ++---------------
>  2 files changed, 3 insertions(+), 36 deletions(-)
>
> diff --git a/runtime/linux/x86_32/architecture_init.c
> b/runtime/linux/x86_32/architecture_init.c
> index f080dc4..f3fb6e6 100644
> --- a/runtime/linux/x86_32/architecture_init.c
> +++ b/runtime/linux/x86_32/architecture_init.c
> @@ -27,28 +27,8 @@ POSSIBILITY OF SUCH DAMAGE.
>  #include <stddef.h>
>  #include "runtime.h"
>
> -void (*kernel_vsyscall)();
> -
> -/* AT_SYSINFO entry has the vsyscall address */
> -#define AT_SYSINFO 32
> -
> -void set_kernel_vsyscall(const auxv_t *auxv)
> -{
> -       if (auxv != NULL) {
> -               const auxv_t *auxv_walk;
> -               for (auxv_walk = auxv; auxv_walk->a_type != 0; auxv_walk++) {
> -                       if (auxv_walk->a_type == AT_SYSINFO) {
> -                               kernel_vsyscall = auxv_walk->a_un.a_fcn;
> -                               return;
> -
> -                       }
> -               }
> -               // ERROR: AT_SYSINFO entry not found
> -       }
> -}
> -
>  void architecture_init(int argc, const char **argv, const char **envp,
>                        const auxv_t *auxv)
>  {
> -       set_kernel_vsyscall(auxv);
> +       /* Do nothing */
>  }
> diff --git a/system/linux/x86_32/system_calls.S
> b/system/linux/x86_32/system_calls.S
> index 8e1d6f9..f11f8ca 100644
> --- a/system/linux/x86_32/system_calls.S
> +++ b/system/linux/x86_32/system_calls.S
> @@ -36,8 +36,6 @@ POSSIBILITY OF SUCH DAMAGE.
>    Paramenter sequence is: %ebx, %ecx, %edx, %esi, %edi and %ebp
>    See, for example:
>    http://www.linuxjournal.com/article/4048
> -
> -   TODO: remove calculation for kernel_vsyscall (use a fixed address)
>  */
>
>
> @@ -45,12 +43,9 @@ syscall1:
>        pushl %ebp
>        movl %esp, %ebp
>        pushl %ebx
> -       call get_abs_address
> -       addl $_GLOBAL_OFFSET_TABLE_, %ebx
> -       movl kernel_vsyscall@GOT(%ebx), %ecx
>        movl 8(%ebp), %eax
>        movl 12(%ebp), %ebx
> -       call *(%ecx)
> +       int $0x80
>        popl %ebx
>        popl %ebp
>        ret
> @@ -60,20 +55,12 @@ syscall3:
>        movl %esp, %ebp
>        pushl %edi
>        pushl %ebx
> -       call get_abs_address
> -       addl $_GLOBAL_OFFSET_TABLE_, %ebx
> -       movl kernel_vsyscall@GOT(%ebx), %edi
>        movl 8(%ebp), %eax
>        movl 12(%ebp), %ebx
>        movl 16(%ebp), %ecx
>        movl 20(%ebp), %edx
> -       call *(%edi)
> +       int $0x80
>        popl %ebx
>        popl %edi
>        popl %ebp
>        ret
> -
> -get_abs_address:
> -       mov (%esp), %ebx
> -       ret
> -
> --
> 1.6.3.3
>
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-- 
 Henrique Dante de Almeida
 hd...@gm...