by Hi there,
I have some doubts regarding the usage of trace(1) or its
equivalent strace(1) (from sunsite.unc.edu and other sites)
for the SunOS
I got my program here (in C) as follows ->
It uses the dlsym() dlopen() functions (these functions are
available using the -ldl switch) to read the addresses of
symbol table entries and use these addresses to access these
values.A convenient way to map strings to virtual addresses
/*****************My program**********************************/
#include <dlfcn.h>
typedef int (*INT_FUNC_PTR)();
main()
{
void *p;
void *h;
int func();
printf("before the dlopen()\n");
h = dlopen(0,1);
printf("after the dlopen()\n");
if (!h) {
printf("I have failed here");
exit(1);
}
printf("before the dlsym()\n");
p = dlsym(h,"func");
printf("after the dlsym()\n");
if (!p ) {
printf("I have failed on second");
exit(1);
}
printf("p = %x\n",p);
printf("address = %x\n",func);
printf("calling the function\n");
((INT_FUNC_PTR) p) ();
}
func()
{
int i;
printf("read in a integer");
scanf("%d",&i);
i += 5 ;
printf("in func value of i = %d\n",i);
}
/************output of strace(1)*****************************/
open("/usr/lib/ld.so", RDONLY, 40300) = 4
read(4, "\81\3\1\b\0\0\80\0\0\0 \0\0\0\0\0\0\0\0\0\0\0\0 \0\0\0\0\0\0\0\0", 32) = 32
mmap(0, 40960, READ|EXEC, PRIVATE, 4, 0) = 0xf77e0000
mmap(0xf77e8000, 8192, READ|WRITE|EXEC, PRIVATE|FIXED, 4, 0x8000) = 0xf77e8000
open("/dev/zero", RDONLY, 7) = 5
getrlimit(STACK, {cur: 8388608, max: 402653184}) = 0
mmap(0xf7800000, 8192, READ|WRITE, PRIVATE|FIXED, 5, 0) = 0xf7800000
close(4) = 0
getuid() = 237 ([euid 237])
getgid() = 102 ([egid 102])
open("/etc/ld.so.cache", RDONLY, 5000100021) = 4
fstat(4, [REG ino 2022 nlnks 1 ...]) = 0
mmap(0, 4096, READ, SHARED, 4, 0) = 0xf77c0000
close(4) = 0
open("/usr/local/lib/X11", RDONLY, 1010525) = 4
fstat(4, [DIR ino 185120 nlnks 15 ...]) = 0
mmap(0xf7802000, 8192, READ|WRITE, PRIVATE|FIXED, 5, 0) = 0xf7802000
getdents(4, {Total: 52 dents}, 8192) = 1180
getdents(4, {Total: 0 dents}, 8192) = 0
close(4) = 0
open("/usr/local/ow/lib", RDONLY, 22) = 4
getdents(4, {Total: 77 dents}, 8192) = 1952
getdents(4, {Total: 0 dents}, 8192) = 0
mmap(0xf7804000, 8192, READ|WRITE, PRIVATE|FIXED, 5, 0) = 0xf7804000
close(4) = 0
open("/usr/local/interviews/lib/SUN4", RDONLY, 21) = -1 (No such file or directory)
open("/usr/lib/libdl.so.1.0", RDONLY, 22770) = 4
read(4, "\81\3\1\b\0\0 \0\0\0 \0\0\0\0\0\0\0\0\84\0\0\0 \0\0\0\0\0\0\0\0", 32) = 32
mmap(0, 16396, READ|EXEC, PRIVATE, 4, 0) = 0xf77a0000
mmap(0xf77a2000, 8192, READ|WRITE|EXEC, PRIVATE|FIXED, 4, 0x2000) = 0xf77a2000
close(4) = 0
open("/usr/lib/libc.so.1.6", RDONLY, 23010) = 4
read(4, "\81\3\1\b\0\6\c0\0\0\0@\0\0\0\0\0\0\0s \0\0\0 \0\0\0\0\0\0\0\0", 32) = 32
mmap(0, 458764, READ|EXEC, PRIVATE, 4, 0) = 0xf7710000
mmap(0xf777c000, 16384, READ|WRITE|EXEC, PRIVATE|FIXED, 4, 0x6c000) = 0xf777c000
close(4) = 0
close(5) = 0
ioctl(1, TCGETA, 0xf7ffec54) = 0
getpagesize() = 0x1000
brk(0x61b0) = 0
brk(0x71b0) = 0
write(1, "before the dlopen()\n", 20) = 20
write(1, "after the dlopen()\n", 19) = 19
write(1, "before the dlsym()\n", 19) = 19
write(1, "after the dlsym()\n", 18) = 18
write(1, "p = 23b0\n", 9) = 9
write(1, "address = 23b0\n", 15) = 15
write(1, "calling the function\n", 21) = 21
ioctl(0, TCGETA, 0xf7ffed6c) = 0
write(1, "read in a integer", 17) = 17
read(0, "10\n", 128) = 3
write(1, "in func value of i = 15\n", 24) = 24
close(0) = 0
close(1) = 0
close(2) = 0
rexit(1) = ?
/***********end of output from strace(1)*****************/
Now my questions to the gurus are ->
what is all the output that is generated before my actual
output? In which phase of the compilation is this done
(I guess it is the link phase but i am not sure)
I do have the source for strace(1) as it is PD,but I am
not able to debug it.
Why is all this output needed?.It appears that this output
is needed before the actual program even though I have
just the standard C library linked in and it is apparently
being done for all programs.
From the first line of the strace(1) output,it looks like
the ld.so program(the dynamic link editor) is being mapped
into the address space of my process).Why is this needed?
Also from the various lines in the output,it is clear that
the shared object versions of the standard C library
(libc.so.x.x) are being mapped into the process.Why?
Also why does the strace(1) program need /usr/local/ow/lib
and the directory entries for the X11 lib?
-> Also more interestingly the calls to dlopen(),dlsym()
exist no more in the output from strace(1),whereas the
calls to scanf() and standard I/O library calls are
mapped to read() and write() system calls as expected.
What is happening here?.
In short I am asking questions about the strace(1) or
the trace(1) program.
I would really appreciate it if some kind soul could
answer these questions.
If someone has the source for strace(1),could someone
lead me along the source?.
thanks.
Ramakrishna Saripalli
e-mail : rsar...@cs.clemson.edu
Man is a beast and usually has no control over his passions.