Hi Eugene,
On 09/19/2018 07:12 PM, Eugene Syromyatnikov wrote:
> Signed-off-by: Eugene Syromyatnikov <evgsyr@xxxxxxxxx>
> ---
> man2/syscall.2 | 42 +++++++++++++++++++++++++++++++++++-------
> 1 file changed, 35 insertions(+), 7 deletions(-)
Great stuff! Patch applied. But I have a question below.
> diff --git a/man2/syscall.2 b/man2/syscall.2
> index 78a91ba..da4173e 100644
> --- a/man2/syscall.2
> +++ b/man2/syscall.2
> @@ -240,14 +240,42 @@ and so on up to
> .IR "trap #0x17"
> for 7-argument system calls.
> .IP [5]
> -The x32 ABI uses the same instruction as the x86-64 ABI and is used on
> -the same processors.
> -To differentiate between them, the bit mask
> +The x32 ABI shares syscall table with x86-64 ABI, however, there are some
> +nuances:
> +.RS
> +.IP \(bu 3
> +In order to signalise that a system call is called under the x32 ABI, additional
> .I __X32_SYSCALL_BIT
> -is bitwise-ORed into the system call number for system calls
> -under the x32 ABI.
> -Both system call tables are available though,
> -so setting the bit is not a hard requirement.
> +is bitwise-ORed with the system call number.
> +The ABI used by a process affects some things, signal handling or syscall
> +restarting, for example.
> +.IP \(bu
> +Since x32 has different sizes for
> +.I long
> +and pointer types, layouts of some (but not all;
> +.B struct timeval
> +or
> +.B struct rlimit
> +are 64-bit, for example) structures are different, and, in order to handle this,
> +additional syscalls are added to the syscall table, starting from number 512
> +(without the
> +.IR __X32_SYSCALL_BIT );
> +for example,
> +.B __NR_readv
> +is defined to 19 for x86-64 ABI and to
> +.IR __X32_SYSCALL_BIT " | " \fB515\fP
> +for x32 ABI.
> +Most of there additional system calls are actually identical to the syscalls
> +used for providing i386 compat; there are some notable exceptions, however,
> +such as
> +.BR preadv2 (2),
> +that uses
> +.B struct iovec
> +entities with 4-byte pointers and sizes ("compat_iovec" in kernel's terms), but
> +passes 8-byte
> +.I pos
> +argument in a single register and not two, as it is implemented in every other
> +ABI.
You say here "every other ABI". Do you mean rather, every other *32-bit* ABI?
Thanks,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
