Compiling Native Code in Android - Pro Android Games - page 50

Debugging with strace
For some reason, the native test program for the library runs in version 1.0 R2 of the SDK, but fails to
load in 1.5 R2. The output gives a clue: the file bionic/linker/linker.c:1581 fails to load the library.
There is a simple Linux tool called strace that can help in this situation.
The strace tool runs the specified command until it exits. It intercepts and records the system calls
that are called by a process and the signals that are received by a process. The name of each system call,
its arguments, and its return value are printed. This is a useful diagnostic and debugging tool for solving
problems with programs for which the source is not readily available. You will find that a great deal can
be learned about a system and its system calls by tracing even ordinary programs.
The topic source provides an Android version of strace . ( strace is now a built into versions 1.5 and
later of the Android SDK.) Let's push it and see what is going on, as shown in Listing 2-9.
Listing 2-9. strace Tool Output
$ adb push strace /data
$ adb shell
# cd /data
# ./strace ./testlib
execve("./testlib", ["./testlib"], [/* 10 vars */]) = 0
getpid() = 835
gettid() = 835
sigaction(SIGILL, {0xb0001a99, [], SA_RESTART}, {SIG_DFL}, 0) = 0
sigaction(SIGABRT, {0xb0001a99, [], SA_RESTART}, {SIG_DFL}, 0) = 0
sigaction(SIGBUS, {0xb0001a99, [], SA_RESTART}, {SIG_DFL}, 0) = 0
stat64("/system/lib/libch02.so", 0xbef9ea58) = -1 ENOENT (No such file or directory)
stat64("/lib/libch02.so", 0xbef9ea58) = -1 ENOENT (No such file or directory)
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40000000
mprotect(0x40000000, 4096, PROT_READ) = 0
fstat64(1, {st_mode=S_IFCHR|0600, st_rdev=makedev(136, 1), ...}) = 0
brk(0) = 0x11000
brk(0x11000) = 0x11000
brk(0x12000) = 0x12000
mprotect(0x40000000, 4096, PROT_READ|PROT_WRITE) = 0
mprotect(0x40000000, 4096, PROT_READ) = 0
ioctl(1, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
write(1, "bionic/linker/linker.c:1581| ERR"..., 70bionic/linker/linker.c:1581| ERROR: 835
could not load 'libch02.so'
) = 70
write(1, "bionic/linker/linker.c:1641| ERR"..., 61bionic/linker/linker.c:1641| ERROR: failed
to link ./testlib
) = 61
write(1, "bionic/linker/linker.c:1741| ERR"..., 71bionic/linker/linker.c:1741| ERROR: CANNOT
LINK EXECUTABLE './testlib'
) = 71
exit_group(-1) = ?
Process 835 detached