178 lines
7.3 KiB
Plaintext
178 lines
7.3 KiB
Plaintext
syscall/README.txt
|
|
==================
|
|
|
|
This directory supports a syscall layer from communication between a
|
|
monolithic, kernel-mode NuttX kernel and a separately built, user-mode
|
|
application set.
|
|
|
|
With most MCUs, NuttX is built as a flat, single executable image
|
|
containing the NuttX RTOS along with all application code. The RTOS code
|
|
and the application run in the same address space and at the same kernel-
|
|
mode privileges. In order to exploit security features of certain
|
|
processors, an alternative build model is also supported: NuttX can
|
|
be built separately as a monolithic, kernel-mode module and the applications
|
|
can be added as a separately built, user-mode module.
|
|
|
|
The syscall layer provided in this directory serves as the communication
|
|
layer from the user-mode application into the kernel-mode RTOS. The
|
|
switch from user-mode to kernel-mode is accomplished using software
|
|
interrupts (SWIs). SWIs are implemented differently and named differently
|
|
by different manufacturers but all work essentially the same: A special
|
|
instruction is executed in user-mode that causes a software generated
|
|
interrupt. The software generated interrupt is caught within the kernel
|
|
and handle in kernel-mode.
|
|
|
|
Header Files
|
|
============
|
|
|
|
include/syscall.h
|
|
|
|
This header file supports general access to SWI facilities. It is simply
|
|
a wrapper file that includes include/sys/syscall.h and
|
|
include/arch/syscall.h.
|
|
|
|
include/sys/syscall.h
|
|
|
|
The SWIs received by the kernel are distinguish by a code that identifies
|
|
how to process the SWI. This header file defines all such codes understood
|
|
by the NuttX kernel.
|
|
|
|
include/arch/syscall.h (or arch/<cpu>/include/syscall.h)
|
|
|
|
This header file is provided by the platform-specific logic and declares
|
|
(or defines) the mechanism for providing software interrupts on this
|
|
platform. The following functions must be declared (or defined) in this
|
|
header file:
|
|
|
|
- SWI with SYS_ call number and one parameter
|
|
|
|
uintptr_t sys_call0(unsigned int nbr);
|
|
|
|
- SWI with SYS_ call number and one parameter
|
|
|
|
uintptr_t sys_call1(unsigned int nbr, uintptr_t parm1);
|
|
|
|
- SWI with SYS_ call number and two parameters
|
|
|
|
uintptr_t sys_call2(unsigned int nbr, uintptr_t parm1, uintptr_t parm2);
|
|
|
|
- SWI with SYS_ call number and three parameters
|
|
|
|
uintptr_t sys_call3(unsigned int nbr, uintptr_t parm1,
|
|
uintptr_t parm2, uintptr_t parm3);
|
|
|
|
- SWI with SYS_ call number and four parameters
|
|
|
|
uintptr_t sys_call4(unsigned int nbr, uintptr_t parm1, uintptr_t parm2,
|
|
uintptr_t parm3, uintptr_t parm4);
|
|
|
|
- SWI with SYS_ call number and five parameters
|
|
|
|
uintptr_t sys_call5(unsigned int nbr, uintptr_t parm1, uintptr_t parm2,
|
|
uintptr_t parm3, uintptr_t parm4, uintptr_t parm5);
|
|
|
|
- SWI with SYS_ call number and six parameters
|
|
|
|
uintptr_t sys_call6(unsigned int nbr, uintptr_t parm1, uintptr_t parm2,
|
|
uintptr_t parm3, uintptr_t parm4, uintptr_t parm5,
|
|
uintptr_t parm6);
|
|
Syscall Database
|
|
================
|
|
|
|
Sycall information is maintained in a database. That "database" is
|
|
implemented as a simple comma-separated-value file, syscall.csv. Most
|
|
spreadsheets programs will accept this format and can be used to maintain
|
|
the syscall database.
|
|
|
|
The format of the CSV file for each line is:
|
|
|
|
Field 1: Function name
|
|
Field 2: The header file that contains the function prototype
|
|
Field 3: Condition for compilation
|
|
Field 4: The type of function return value.
|
|
Field 5 - N+5: The type of each of the N formal parameters of the function
|
|
Fields N+5 - : If the last parameter is "...", then the following fields
|
|
provide the type and number of of possible optional parameters.
|
|
See note below about variadic functions
|
|
|
|
Each type field has a format as follows:
|
|
|
|
type name:
|
|
For all simpler types
|
|
formal type | actual type:
|
|
For array types where the form of the formal (eg. int parm[2])
|
|
differs from the type of actual passed parameter (eg. int*). This
|
|
is necessary because you cannot do simple casts to array types.
|
|
formal type | union member actual type | union member fieldname:
|
|
A similar situation exists for unions. For example, the formal
|
|
parameter type union sigval -- You cannot cast a uintptr_t to
|
|
a union sigval, but you can cast to the type of one of the union
|
|
member types when passing the actual parameter. Similarly, we
|
|
cannot cast a union sigval to a uinptr_t either. Rather, we need
|
|
to cast a specific union member fieldname to uintptr_t.
|
|
|
|
Variadic Functions:
|
|
|
|
General variadic functions which may have an arbitrary number of argument
|
|
or arbitrary types cannot be represented as system calls. syslog() is a
|
|
good example. Normally you would work around this by using the non-
|
|
variadic form of the OS interface that accepts a va_list as an argument,
|
|
vsyslog() in this case.
|
|
|
|
There there are many functions that have a variadic form but take only
|
|
one or two arguments optional arguments. There can be handled as system
|
|
calls, but only by treating them as though they had a fixed number of
|
|
arguments.
|
|
|
|
These are are handled in syscall.csv by appending the number and type of
|
|
optional arguments. For example, consider the open() OS interface. Its
|
|
prototype is:
|
|
|
|
int open(const char *path, int oflag, ...);
|
|
|
|
In reality, open may take only a single optional argument of type mode_t
|
|
and is represented in syscall.cvs like this:
|
|
|
|
"open","fcntl.h","","int","const char*","int","...","mode_t"
|
|
|
|
The existence of the "mode_t" tells tools/mksyscall that there is at most
|
|
one optional parameter and, if present, it is of type mode_t.
|
|
|
|
NOTE: This CSV file is used both to support the generate of trap information,
|
|
but also for the generation of symbol tables. See nuttx/tools/README.txt
|
|
and nuttx/lib/README.txt for further information.
|
|
|
|
Auto-Generated Files
|
|
====================
|
|
|
|
Stubs and proxies for the sycalls are automatically generated from this CSV
|
|
database. Here the following definition is used:
|
|
|
|
Proxy - A tiny bit of code that executes in the user space. A proxy
|
|
has exactly the same function prototype as does the "real" function
|
|
for which it proxies. However, it only serves to map the function
|
|
call into a syscall, marshaling all of the system call parameters
|
|
as necessary.
|
|
|
|
Stub - Another tiny bit of code that executes within the NuttX kernel
|
|
that is used to map a software interrupt received by the kernel to
|
|
a kernel function call. The stubs receive the marshaled system
|
|
call data, and perform the actually kernel function call (in
|
|
kernel-mode) on behalf of the proxy function.
|
|
|
|
Sub-Directories
|
|
===============
|
|
|
|
stubs - Autogenerated stub files are placed in this directory.
|
|
proxies - Autogenerated proxy files are placed in this directory.
|
|
|
|
mksyscall
|
|
=========
|
|
|
|
mksyscall is C program that is used used during the initial NuttX build
|
|
by the logic in the top-level syscall/ directory. Information about the
|
|
stubs and proxies is maintained in a comma separated value (CSV) file
|
|
in the syscall/ directory. The mksyscall program will accept this CVS
|
|
file as input and generate all of the required proxy or stub files as
|
|
output. See tools/README.txt for additional information.
|