#include <unistd.h> #include <sys/syscall.h> /* SYS_xxx の定義用 */ long syscall(long number, ...);
glibc 向けの機能検査マクロの要件 (feature_test_macros(7) 参照):
syscall():
syscall() は、システムコールを行う前に CPU レジスターを保存し、システムコールから返った際にレジスターを復元し、システムコールが返したエラーを errno(3) に格納する。
システムコールのシンボル定数は、ヘッダーファイル <sys/syscall.h> に書かれている。
For example, on the ARM architecture Embedded ABI (EABI), a 64-bit value (e.g., long long) must be aligned to an even register pair. Thus, using syscall() instead of the wrapper provided by glibc, the readahead(2) system call would be invoked as follows on the ARM architecture with the EABI in little endian mode:
syscall(SYS_readahead, fd, 0,
(unsigned int) (offset & 0xFFFFFFFF),
(unsigned int) (offset >> 32),
count);
Since the offset argument is 64 bits, and the first argument (fd) is passed in r0, the caller must manually split and align the 64-bit value so that it is passed in the r2/r3 register pair. That means inserting a dummy value into r1 (the second argument of 0). Care also must be taken so that the split follows endian conventions (according to the C ABI for the platform).
Similar issues can occur on MIPS with the O32 ABI, on PowerPC and parisc with the 32-bit ABI, and on Xtensa.
Note that while the parisc C ABI also uses aligned register pairs, it uses a shim layer to hide the issue from user space.
次のシステムコールに影響がある: fadvise64_64(2), ftruncate64(2), posix_fadvise(2), pread64(2), pwrite64(2), readahead(2), sync_file_range(2), truncate64(2)
This does not affect syscalls that manually split and assemble 64-bit values such as _llseek(2), preadv(2), preadv2(2), pwritev(2), and pwritev2(2). Welcome to the wonderful world of historical baggage.
The first table lists the instruction used to transition to kernel mode (which might not be the fastest or best way to transition to the kernel, so you might have to refer to vdso(7)), the register used to indicate the system call number, the register(s) used to return the system call result, and the register used to signal an error.
Arch/ABI | Instruction | System | Ret | Ret | Error | 備考 |
call # | val | val2 | ||||
alpha | callsys | v0 | v0 | a4 | a3 | 1, 6 |
arc | trap0 | r8 | r0 | - | - | |
arm/OABI | swi NR | - | r0 | - | - | 2 |
arm/EABI | swi 0x0 | r7 | r0 | r1 | - | |
arm64 | svc #0 | w8 | x0 | x1 | - | |
blackfin | excpt 0x0 | P0 | R0 | - | - | |
i386 | int $0x80 | eax | eax | edx | - | |
ia64 | break 0x100000 | r15 | r8 | r9 | r10 | 1, 6 |
m68k | trap #0 | d0 | d0 | - | - | |
microblaze | brki r14,8 | r12 | r3 | - | - | |
mips | syscall | v0 | v0 | v1 | a3 | 1, 6 |
nios2 | trap | r2 | r2 | - | r7 | |
parisc | ble 0x100(%sr2, %r0) | r20 | r28 | - | - | |
powerpc | sc | r0 | r3 | - | r0 | 1 |
powerpc64 | sc | r0 | r3 | - | cr0.SO | 1 |
riscv | ecall | a7 | a0 | a1 | - | |
s390 | svc 0 | r1 | r2 | r3 | - | 3 |
s390x | svc 0 | r1 | r2 | r3 | - | 3 |
superh | trap #0x17 | r3 | r0 | r1 | - | 4, 6 |
sparc/32 | t 0x10 | g1 | o0 | o1 | psr/csr | 1, 6 |
sparc/64 | t 0x6d | g1 | o0 | o1 | psr/csr | 1, 6 |
tile | swint1 | R10 | R00 | - | R01 | 1 |
x86-64 | syscall | rax | rax | rdx | - | 5 |
x32 | syscall | rax | rax | rdx | - | 5 |
xtensa | syscall | a2 | a2 | - | - |
Notes:
2 つ目の表は、システムコールの引数を渡すのに使用されるレジスターの一覧である。
Arch/ABI | arg1 | arg2 | arg3 | arg4 | arg5 | arg6 | arg7 | 備考 |
alpha | a0 | a1 | a2 | a3 | a4 | a5 | - | |
arc | r0 | r1 | r2 | r3 | r4 | r5 | - | |
arm/OABI | r0 | r1 | r2 | r3 | r4 | r5 | r6 | |
arm/EABI | r0 | r1 | r2 | r3 | r4 | r5 | r6 | |
arm64 | x0 | x1 | x2 | x3 | x4 | x5 | - | |
blackfin | R0 | R1 | R2 | R3 | R4 | R5 | - | |
i386 | ebx | ecx | edx | esi | edi | ebp | - | |
ia64 | out0 | out1 | out2 | out3 | out4 | out5 | - | |
m68k | d1 | d2 | d3 | d4 | d5 | a0 | - | |
microblaze | r5 | r6 | r7 | r8 | r9 | r10 | - | |
mips/o32 | a0 | a1 | a2 | a3 | - | - | - | 1 |
mips/n32,64 | a0 | a1 | a2 | a3 | a4 | a5 | - | |
nios2 | r4 | r5 | r6 | r7 | r8 | r9 | - | |
parisc | r26 | r25 | r24 | r23 | r22 | r21 | - | |
powerpc | r3 | r4 | r5 | r6 | r7 | r8 | r9 | |
powerpc64 | r3 | r4 | r5 | r6 | r7 | r8 | - | |
riscv | a0 | a1 | a2 | a3 | a4 | a5 | - | |
s390 | r2 | r3 | r4 | r5 | r6 | r7 | - | |
s390x | r2 | r3 | r4 | r5 | r6 | r7 | - | |
superh | r4 | r5 | r6 | r7 | r0 | r1 | r2 | |
sparc/32 | o0 | o1 | o2 | o3 | o4 | o5 | - | |
sparc/64 | o0 | o1 | o2 | o3 | o4 | o5 | - | |
tile | R00 | R01 | R02 | R03 | R04 | R05 | - | |
x86-64 | rdi | rsi | rdx | r10 | r8 | r9 | - | |
x32 | rdi | rsi | rdx | r10 | r8 | r9 | - | |
xtensa | a6 | a3 | a4 | a5 | a8 | a9 | - |
Notes:
これらの表にはすべての呼び出し規約が記載されているわけではない点に注意すること --- アーキテクチャーによっては、ここに記載されていない他のレジスターが見境なく上書きされる場合もある。
int
main(int argc, char *argv[])
{
pid_t tid;
tid = syscall(SYS_gettid);
syscall(SYS_tgkill, getpid(), tid, SIGHUP);
}