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seccomp.2: Add subsection on seccomp-specific BPF details 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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Michael Kerrisk 2014-12-30 12:35:39 +01:00
parent 93b9a9eeff
commit cecc8c48ba
1 changed files with 28 additions and 0 deletions
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man2/seccomp.2
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@ -463,6 +463,34 @@ provides a superset of the functionality provided by the
.BR PR_SET_SECCOMP
operation (which does not support
.IR flags ).
.\" FIXME Please review the following new subsection {{{
.SS Seccomp-specific BPF details
Note the following BPF details specific to seccomp filters:
.IP * 3
The
.B BPF_H
and
.B BPF_B
size modifiers are not supported: all operations must load and store
(4-byte) words
.RB ( BPF_W ).
.IP *
To access the contents of the
.I seccomp_data
buffer, use the
.B BPF_ABS
addressing mode modifier.
.\" FIXME What is the significance of the line
.\" ftest->code = BPF_LDX | BPF_W | BPF_ABS;
.\" in kernel/seccomp.c::seccomp_check_filter()?
.IP *
The
.B BPF_LEN
addressing mode modifier yields an immediate mode operand
whose value is the size of the
.IR seccomp_data
buffer.
.\" FIXME End of new subsection for review }}}
.SH EXAMPLE
The program below accepts four or more arguments.
The first three arguments are a system call number,