そこで、次の「Hello World!」プログラムを使用してシステムコールを理解しようとしています。
#include <stdio.h>
int main(){
printf("Hello World!\n");
return 0;
}
次に、実行可能ファイルに対して strace を実行すると、次の結果が得られます。
execve("./hello", ["./hello"], [/* 62 vars */]) = 0
brk(0) = 0x85a5000
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb774f000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/home/miguel/GNUstep/Library/Libraries/tls/i686/sse2/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/home/miguel/GNUstep/Library/Libraries/tls/i686/sse2", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/home/miguel/GNUstep/Library/Libraries/tls/i686/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/home/miguel/GNUstep/Library/Libraries/tls/i686", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/home/miguel/GNUstep/Library/Libraries/tls/sse2/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/home/miguel/GNUstep/Library/Libraries/tls/sse2", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/home/miguel/GNUstep/Library/Libraries/tls/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/home/miguel/GNUstep/Library/Libraries/tls", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/home/miguel/GNUstep/Library/Libraries/i686/sse2/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/home/miguel/GNUstep/Library/Libraries/i686/sse2", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/home/miguel/GNUstep/Library/Libraries/i686/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/home/miguel/GNUstep/Library/Libraries/i686", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/home/miguel/GNUstep/Library/Libraries/sse2/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/home/miguel/GNUstep/Library/Libraries/sse2", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/home/miguel/GNUstep/Library/Libraries/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/home/miguel/GNUstep/Library/Libraries", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/usr/lib/tls/i686/sse2/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/tls/i686/sse2", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/usr/lib/tls/i686/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/tls/i686", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/usr/lib/tls/sse2/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/tls/sse2", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/usr/lib/tls/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/tls", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/usr/lib/i686/sse2/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/i686/sse2", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/usr/lib/i686/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/i686", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/usr/lib/sse2/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/sse2", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/usr/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\1\1\1\3\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\300\177\1\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0755, st_size=2035943, ...}) = 0
mmap2(NULL, 1801892, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb7573000
mmap2(0xb7724000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1b0000) = 0xb7724000
mmap2(0xb7729000, 7844, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb7729000
close(3) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7572000
set_thread_area({entry_number:-1, base_addr:0xb7572700, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0 (entry_number:6)
mprotect(0xb7724000, 12288, PROT_READ) = 0
mprotect(0xb7750000, 4096, PROT_READ) = 0
fstat64(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 1), ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7571000
write(1, "Hello World!\n", 13) = 13
exit_group(0) = ?
+++ exited with 0 +++
ディスクに存在しないライブラリを開こうとするシステム コールが多数あります。なぜこのプログラムはそれらのファイルにアクセスしようとしているのでしょうか。これを防ぐにはどうすればよいですか。
変数 LD_LIBRARY_PATH の内容は次のとおりです。
/home/miguel/GNUstep/Library/Libraries:/usr/lib
答え1
これはすべて完全に正常です。ライブラリ検索の失敗を防ぐことはできません。
execve("./hello", ["./hello"], [/* 62 vars */]) = 0
これがあなたのプログラムの始まりです。動的にリンクされているため、最初に実行されるコードはdynamic loader。
brk(0) = 0x85a5000
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb774f000
ダイナミック ローダーはヒープ領域を割り当てています。
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
ダイナミック ローダーは、プリロードするダイナミック ライブラリがあるかどうかを確認します。 ダイナミック ライブラリはありません。
open("/home/miguel/GNUstep/Library/Libraries/tls/i686/sse2/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/home/miguel/GNUstep/Library/Libraries/tls/i686/sse2", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/home/miguel/GNUstep/Library/Libraries/tls/i686/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/home/miguel/GNUstep/Library/Libraries/tls/i686", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/home/miguel/GNUstep/Library/Libraries/tls/sse2/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/home/miguel/GNUstep/Library/Libraries/tls/sse2", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/home/miguel/GNUstep/Library/Libraries/tls/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/home/miguel/GNUstep/Library/Libraries/tls", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/home/miguel/GNUstep/Library/Libraries/i686/sse2/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/home/miguel/GNUstep/Library/Libraries/i686/sse2", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/home/miguel/GNUstep/Library/Libraries/i686/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/home/miguel/GNUstep/Library/Libraries/i686", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/home/miguel/GNUstep/Library/Libraries/sse2/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/home/miguel/GNUstep/Library/Libraries/sse2", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/home/miguel/GNUstep/Library/Libraries/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/home/miguel/GNUstep/Library/Libraries", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/usr/lib/tls/i686/sse2/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/tls/i686/sse2", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/usr/lib/tls/i686/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/tls/i686", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/usr/lib/tls/sse2/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/tls/sse2", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/usr/lib/tls/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/tls", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/usr/lib/i686/sse2/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/i686/sse2", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/usr/lib/i686/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/i686", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/usr/lib/sse2/libc.so.6", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/sse2", 0xbf8df160) = -1 ENOENT (No such file or directory)
open("/usr/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
ダイナミック ローダーはlibc6、標準ライブラリである を探しています。 いくつかのディレクトリを検索します。まず で指定されたディレクトリを検索しLD_LIBRARY_PATH、次に にリストされているディレクトリを/etc/ld.so.conf検索します (詳細についてはマニュアルを参照してください)。 各ディレクトリで、ローダーはまずいくつかのサブディレクトリをチェックします。どのハードウェア機能が存在するかを判断します (P6の指示、SSE2) を実行し、これらの追加機能を使用してより効率的に実行できるライブラリ バイナリのバージョンを探します。すべての機能を使用できるものが見つからない場合は、より汎用的なバージョンを探します。最終的に、ライブラリは標準のシステム ディレクトリ内の非特殊バージョンで見つかります。
read(3, "\177ELF\1\1\1\3\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\300\177\1\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0755, st_size=2035943, ...}) = 0
mmap2(NULL, 1801892, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb7573000
mmap2(0xb7724000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1b0000) = 0xb7724000
mmap2(0xb7729000, 7844, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb7729000
close(3) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7572000
set_thread_area({entry_number:-1, base_addr:0xb7572700, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0 (entry_number:6)
mprotect(0xb7724000, 12288, PROT_READ) = 0
mprotect(0xb7750000, 4096, PROT_READ) = 0
標準ライブラリがロードされ、その初期化コードが実行されます。
fstat64(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 1), ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7571000
これは呼び出しを実行した結果ですprintf。
write(1, "Hello World!\n", 13) = 13
exit_group(0) = ?
これはプログラムの終了であり、stdout バッファのフラッシュが含まれます。