| libsyscall: A system call handling framework |
| ============================================ |
| |
| libsyscall provides a table based framework for handling system calls. A |
| user of this library just provides a file named syscall_table.h with a |
| table of function pointers defined using the DEF_SYSCALL macro: |
| |
| DEF_SYSCALL(nr, fn, rtype, nargs, ...) |
| |
| nr : system call number to use. Should not be zero or negative |
| fn : name of the system call. E.g, "read", "write" etc. |
| rtype: type of return value for this syscall |
| nargs: number of arguments accepted by this system call. System calls |
| supported by this library can take upto 4 arguments. |
| |
| These parameters are followed by types (and optionally names) names of |
| arguments to the system call. This information is useful for |
| auto-generating C function prototypes for userspace (see below). |
| |
| An example system call table: |
| |
| DEF_SYSCALL(0x3, read, long, 3, uint32_t fd, void* msg, uint32_t size) |
| DEF_SYSCALL(0x4, write, long, 3, uint32_t fd, void* msg, uint32_t size) |
| DEF_SYSCALL(0x5, open, long, 0) |
| DEF_SYSCALL(0x2d, brk, long, 1, uint32_t brk) |
| DEF_SYSCALL(0x36, ioctl, long, 3, uint32_t d, uint32_t req, void *msg) |
| DEF_SYSCALL(0x4e, gettimeofday, long, 0) |
| DEF_SYSCALL(0x5b, munmap, long, 2, addr_t addr, uint32_t size) |
| DEF_SYSCALL(0x7d, mprotect, long, 0) |
| DEF_SYSCALL(0xa2, usleep, long, 1, struct timespec *ts) |
| DEF_SYSCALL(0xc0, mmap2, long, 4, addr_t addr, uint32_t length, uint32_t prot, uint32_t flags) |
| DEF_SYSCALL(0xc5, fstat, long, 0) |
| DEF_SYSCALL(0xdc, madvise, long, 0) |
| DEF_SYSCALL(0xe0, gettid, long, 0) |
| DEF_SYSCALL(0xf8, exit_group, long, 0) |
| DEF_SYSCALL(0x107, clock_gettime, long, 0) |
| |
| Function names get expanded to sys_{fn_name} by the macro in the kernel. |
| In the table above, syscall 0x3 "read" causes sys_read() to be called, |
| and syscall 0x4 causes sys_write() to be called by the syscall hander. |
| |
| Syscall vector handler and ABI |
| ============================== |
| |
| The system call vector handler provided as part of this library simply |
| jumps to the right function in the table based on system call number |
| provided in a register. |
| |
| The system call ABI for a given architecture is documented in |
| arch/$(ARCH)/syscall.S |
| |
| System calls are executed with interrupts turned on. |
| |
| Stub and C prototype autogeneration |
| =================================== |
| |
| This library also provides a python script to generate system call stub |
| functions for userspace in GNU assembler syntax and a C header file with |
| macros defining syscall numbers and C function prototypes for all |
| functions. For more info: |
| |
| python stubgen.py --help |
