I have never seen this assembly syntax.
#include "syscall.h"
#include "traps.h"
#define SYSCALL(name) \
.globl name; \
name: \
movl $SYS_ ## name, %eax; \
int $T_SYSCALL; \
ret
SYSCALL(fork)
SYSCALL(exit)
SYSCALL(wait)
SYSCALL(pipe)
SYSCALL(read)
SYSCALL(write)
SYSCALL(close)
SYSCALL(kill)
SYSCALL(exec)
SYSCALL(open)
SYSCALL(mknod)
SYSCALL(unlink)
SYSCALL(fstat)
SYSCALL(link)
SYSCALL(mkdir)
SYSCALL(chdir)
SYSCALL(dup)
SYSCALL(getpid)
SYSCALL(sbrk)
SYSCALL(sleep)
SYSCALL(uptime)
For assembly language file with extension .S, gcc will use a C preprocessor.
In C, \ at the end of line means that "connect the next line to this line".
For that reason, the macro becomes
#define SYSCALL(name) .globl name; name: movl $SYS_ ## name, %eax; int $T_SYSCALL; ret
## operator will concatenate the tokens in its left and right.
Therefore, for example, SYSCALL(fork) will be expanded to
.globl fork; fork: movl $SYS_fork, %eax; int $T_SYSCALL; ret
This means
make the identifire fork public
define a label fork (this will work as a function)
in this function
assign an immediate value SYS_fork to register %eax
generate an interrupt with code T_SYSCALL
return from this function
Related
First of all, forgive my awful english.....
This is the prototype
FILE *popen(const char* cmd_string, const char* type);
Here is my question, the book says that when popen function is called, it will call exec to get a shell to execute the cmd_string we give to popen, but I'm not sure which shell will exec get, so can anyone give me an answer?
/bin/sh : From the doc:
The command argument is a pointer to a null-terminated string
containing a shell command line. This command is passed to /bin/sh
using the -c flag; interpretation, if any, is performed by the shell.
Let's try and see:
$ cat test.c
#include <stdio.h>
int main() {
FILE *fp;
char var[5];
fp = popen("echo $0", "r");
fgets(var, 5, fp);
printf("%s", var);
}
$ gcc -Wall test.c
$ ./a.out
sh
I am new to Frama-C framework and I am trying to do some contract testing with C programs. I intend to use E-ACSL plugin for this, and I tried a test program to see how it works, but I get some compilation errors. Here is my code:
#include <stdio.h>
#include <stdlib.h>
int main(void) {
int x = 0;
/*# assert x == 1;*/
/*# assert x == 0;*/
return 0;
}
Then, here is the Frama-C annotated code:
/* Generated by Frama-C */
#include "stdio.h"
#include "stdlib.h"
struct __e_acsl_mpz_struct {
int _mp_alloc ;
int _mp_size ;
unsigned long *_mp_d ;
};
typedef struct __e_acsl_mpz_struct __e_acsl_mpz_struct;
typedef __e_acsl_mpz_struct ( __attribute__((__FC_BUILTIN__)) __e_acsl_mpz_t)[1];
/*# ghost extern int __e_acsl_init; */
/*# ghost extern int __e_acsl_internal_heap; */
extern size_t __e_acsl_heap_allocation_size;
/*#
predicate diffSize{L1, L2}(ℤ i) =
\at(__e_acsl_heap_allocation_size,L1) -
\at(__e_acsl_heap_allocation_size,L2) ≡ i;
*/
int main(void)
{
int __retres;
int x = 0;
/*# assert x ≡ 1; */ ;
/*# assert x ≡ 0; */ ;
__retres = 0;
return __retres;
}
Finally, I try to compile it with gcc and the flags the manual indicates (page 13) but I get the following errors (and warnings):
$ gcc monitored_second.c -o monitored_second -leacsl -leacsl-gmp -leacsl -jemalloc -lpthread -lm
monitored_second.c:10:1: warning: ‘__FC_BUILTIN__’ attribute directive ignored [-Wattributes]
typedef __e_acsl_mpz_struct ( __attribute__((__FC_BUILTIN__)) __e_acsl_mpz_t)[1];
monitored_second.c:18:55: warning: ‘__FC_BUILTIN__’ attribute directive ignored [-Wattributes]
int line);
^
monitored_second.c:25:60: warning: ‘__FC_BUILTIN__’ attribute directive ignored [-Wattributes]
size_t ptr_size);
^
/usr/bin/ld: cannot find -leacsl
/usr/bin/ld: cannot find -leacsl-jemalloc
collect2: error: ld returned 1 exit status
I've also removed the "-rtl-bittree" label because it returns another error.
Frama-C version is the latest: Sulfur-20171101
Got any idea of what is happening?
Thanks!
Normally, you should have a script called e-acsl-gcc.sh installed in the same directory as frama-c binary, that can take care of calling gcc with appropriate options. Its basic usage is documented in section 2.2 of the manual, and man e-acsl-gcc.sh gives more details on the options that can be used. In short, you should be able to type
e-acsl-gcc.sh -c \
--oexec-eacsl=first_monitored \
--oexec=first \
--ocode=first_monitored.i \
first.i
to obtain
an executable first_monitored with the e-acsl instrumentation
an executable first with the original program
a source file first_monitored.i with the e-acsl generated C code
Edit Looking at the linking command used by the script, I'd say that the command line proposed earlier in the manual is out of date (in particular, it refers to eacsl-jemalloc whereas e-acsl-gcc.sh seems to prefer eacsl-dlmalloc), which could probably be reported as a bug at https://bts.frama-c.com
Can someone explain why the following code yields different results on the second printf if I comment the first printf line or not, in 64 bits?
/* gcc -O0 -o test test.c */
#include <stdio.h>
#include <stdlib.h>
int main() {
char a[20] = {0};
char b = 'a';
int count=-1;
// printf("%.16llx %.16llx\n", a, &b);
printf("%x\n", *(a+count));
return 0;
}
I get the following results for the second printf:
commented: 0
uncommented: 61
Thanks in advance!
iansus
Can someone explain why the following code yields different results on the second printf if I comment the first printf line or not
Your program uses a[-1], and thus exhibits undefined behavior. Anything can happen, and figuring out exactly why one or the other thing happenes is pointless.
The precise reason is that you are reading memory that gets written to by the first printf (when commented in).
I get a different result (which is expected with undefined behavior):
// with first `printf` commented out:
ffffffff
// with it commented in:
00007fffffffdd20 00007fffffffdd1b
ffffffff
You could see where that memory is written to by setting a GDB watchpoint on it:
(gdb) p a[-1]
$1 = 0 '\000'
(gdb) p &a[-1]
$2 = 0x7fffffffdd1f ""
(gdb) watch *(int*)0x7fffffffdd1f
Hardware watchpoint 4: *(int*)0x7fffffffdd1f
(gdb) c
Continuing.
Hardware watchpoint 4: *(int*)0x7fffffffdd1f
Old value = 0
New value = 255
main () at t.c:12
12 printf("%.16llx %.16llx\n", a, &b);
It my case above, the value is written as part of initializing count=-1. That is, with my version of gcc, count is located just before a[0]. But this may depend on compiler version, exactly how this compiler was built, etc. etc.
I have dynamic library created as follows
cat myfile.cc
struct Tcl_Interp;
extern "C" int My_Init(Tcl_Interp *) { return 0; }
1) complile the cc file
g++ -fPIC -c myfile.cc
2) Creating a shared library
g++ -static-libstdc++ -static-libgcc -shared -o libmy.so myfile.o -L/tools/linux64/qt-4.6.0/lib -lQtCore -lQtGui
3) load the library from a TCL proc
then I give command
tclsh
and given command
% load libmy.so
is there any C++ function/ Qt equivalent to load that can load the shared library on demand from another C++ function.
My requirement is to load the dynamic library on run time inside the function and then use the qt functions directly
1) load the qt shared libraries (for lib1.so)
2) call directly the functions without any call for resolve
For example we have dopen, but for that for each function call we have to call dsym. My requirement is only call for shared library then directly call those functions.
You want boilerplate-less delay loading. On Windows, MSVC implements delay loading by emitting a stub that resolves the function through a function pointer. You can do the same. First, let's observe that function pointers and functions are interchangeable if all you do is call them. The syntax for invoking a function or a function pointer is the same:
void foo_impl() {}
void (*foo)() = foo_impl;
int main() {
foo_impl();
foo();
}
The idea is to set the function pointer initially to a thunk that will resolve the real function at runtime:
extern void (*foo)();
void foo_thunk() {
foo = QLibrary::resolve("libmylib", "foo");
if (!foo) abort();
return foo();
}
void (*foo)() = foo_thunk;
int main() {
foo(); // calls foo_thunk to resolve foo and calls foo from libmylib
foo(); // calls foo from libmylib
}
When you first call foo, it will really call foo_thunk, resolve the function address, and call real foo implementation.
To do this, you can split the library into two libraries:
The library implementation. It is unaware of demand-loading.
A demand-load stub.
The executable will link to the demand-load stub library; that is either static or dynamic. The demand-load stub will automatically resolve the symbols at runtime and call into the implementation.
If you're clever, you can design the header for the implementation such that the header itself can be used to generate all the stubs without having to enter their details twice.
Complete Example
Everything follows, it's also available from https://github.com/KubaO/stackoverflown/tree/master/questions/demand-load-39291032
The top-level project consists of:
lib1 - the dynamic library
lib1_demand - the static demand-load thunk for lib1
main - the application that uses lib1_demand
demand-load-39291032.pro
TEMPLATE = subdirs
SUBDIRS = lib1 lib1_demand main
main.depends = lib1_demand
lib1_demand.depends = lib1
We can factor out the cleverness into a separate header. This header allows us to define the library interface so that the thunks can be automatically generated.
The heavy use of preprocessor and a somewhat redundant syntax is needed due to limitations of C. If you wanted to implement this for C++ only, there'd be no need to repeat the argument list.
demand_load.h
// Configuration macros:
// DEMAND_NAME - must be set to a unique identifier of the library
// DEMAND_LOAD - if defined, the functions are declared as function pointers, **or**
// DEMAND_BUILD - if defined, the thunks and function pointers are defined
#if defined(DEMAND_FUN)
#error Multiple inclusion of demand_load.h without undefining DEMAND_FUN first.
#endif
#if !defined(DEMAND_NAME)
#error DEMAND_NAME must be defined
#endif
#if defined(DEMAND_LOAD)
// Interface via a function pointer
#define DEMAND_FUN(ret,name,args,arg_call) \
extern ret (*name)args;
#elif defined(DEMAND_BUILD)
// Implementation of the demand loader stub
#ifndef DEMAND_CAT
#define DEMAND_CAT_(x,y) x##y
#define DEMAND_CAT(x,y) DEMAND_CAT_(x,y)
#endif
void (* DEMAND_CAT(resolve_,DEMAND_NAME)(const char *))();
#if defined(__cplusplus)
#define DEMAND_FUN(ret,name,args,arg_call) \
extern ret (*name)args; \
ret name##_thunk args { \
name = reinterpret_cast<decltype(name)>(DEMAND_CAT(resolve_,DEMAND_NAME)(#name)); \
return name arg_call; \
}\
ret (*name)args = name##_thunk;
#else
#define DEMAND_FUN(ret,name,args,arg_call) \
extern ret (*name)args; \
ret name##_impl args { \
name = (void*)DEMAND_CAT(resolve_,DEMAND_NAME)(#name); \
name arg_call; \
}\
ret (*name)args = name##_impl;
#endif // __cplusplus
#else
// Interface via a function
#define DEMAND_FUN(ret,name,args,arg_call) \
ret name args;
#endif
Then, the dynamic library itself:
lib1/lib1.pro
TEMPLATE = lib
SOURCES = lib1.c
HEADERS = lib1.h
INCLUDEPATH += ..
DEPENDPATH += ..
Instead of declaring the functions directly, we'll use DEMAND_FUN from demand_load.h. If DEMAND_LOAD_LIB1 is defined when the header is included, it will offer a demand-load interface to the library. If DEMAND_BUILD is defined, it'll define the demand-load thunks. If neither is defined, it will offer a normal interface.
We take care to undefine the implementation-specific macros so that the global namespace is not polluted. We can then include multiple libraries the project, each one individually selectable between demand- and non-demand loading.
lib1/lib1.h
#ifndef LIB_H
#define LIB_H
#ifdef __cplusplus
extern "C" {
#endif
#define DEMAND_NAME LIB1
#ifdef DEMAND_LOAD_LIB1
#define DEMAND_LOAD
#endif
#include "demand_load.h"
#undef DEMAND_LOAD
DEMAND_FUN(int, My_Add, (int i, int j), (i,j))
DEMAND_FUN(int, My_Subtract, (int i, int j), (i,j))
#undef DEMAND_FUN
#undef DEMAND_NAME
#ifdef __cplusplus
}
#endif
#endif
The implementation is uncontroversial:
lib1/lib1.c
#include "lib1.h"
int My_Add(int i, int j) {
return i+j;
}
int My_Subtract(int i, int j) {
return i-j;
}
For the user of such a library, demand loading is reduced to defining one macro and using the thunk library lib1_demand instead of the dynamic library lib1.
main/main.pro
if (true) {
# Use demand-loaded lib1
DEFINES += DEMAND_LOAD_LIB1
LIBS += -L../lib1_demand -llib1_demand
} else {
# Use direct-loaded lib1
LIBS += -L../lib1 -llib1
}
QT = core
CONFIG += console c++11
CONFIG -= app_bundle
TARGET = demand-load-39291032
TEMPLATE = app
INCLUDEPATH += ..
DEPENDPATH += ..
SOURCES = main.cpp
main/main.cpp
#include "lib1/lib1.h"
#include <QtCore>
int main() {
auto a = My_Add(1, 2);
Q_ASSERT(a == 3);
auto b = My_Add(3, 4);
Q_ASSERT(b == 7);
auto c = My_Subtract(5, 7);
Q_ASSERT(c == -2);
}
Finally, the implementation of the thunk. Here we have a choice between using dlopen+dlsym or QLibrary. For simplicity, I opted for the latter:
lib1_demand/lib1_demand.pro
QT = core
TEMPLATE = lib
CONFIG += staticlib
INCLUDEPATH += ..
DEPENDPATH += ..
SOURCES = lib1_demand.cpp
HEADERS = ../demand_load.h
lib1_demand/lib1_demand.cpp
#define DEMAND_BUILD
#include "lib1/lib1.h"
#include <QLibrary>
void (* resolve_LIB1(const char * name))() {
auto f = QLibrary::resolve("../lib1/liblib1", name);
return f;
}
Quite apart from the process of loading a library into your C++ code (which Kuber Ober's answer covers just fine) the code that you are loading is wrong; even if you manage to load it, your code will crash! This is because you have a variable of type Tcl_Interp at file scope; that's wrong use of the Tcl library. Instead, the library provides only one way to obtain a handle to an interpreter context, Tcl_CreateInterp() (and a few other functions that are wrappers round it), and that returns a Tcl_Interp* that has already been initialised correctly. (Strictly, it actually returns a handle to what is effectively an internal subclass of Tcl_Interp, so you really can't usefully allocate one yourself.)
The correct usage of the library is this:
Tcl_FindExecutable(NULL); // Or argv[0] if you have it
Tcl_Interp *interp = Tcl_CreateInterp();
// And now, you can use the rest of the API as you see fit
That's for putting a Tcl interpreter inside your code. To do it the other way round, you create an int My_Init(Tcl_Interp*) function as you describe and it is used to tell you where the interpreter is, but then you wouldn't be asking how to load the code, as Tcl has reasonable support for that already.
I am trying to compile my 1st Assembler program for UNIX, but get a lot of errors. For example, this code (expected to read and write a number from keyboard) gives me "Segmentation fault" message:
.data
.code32
printf_format:
.string "%d\n"
scanf_format:
.string "%d"
number:
.space 4
.text
.globl main
main:
pushl $number
pushl $scanf_format
call scanf
addl $8, %esp
pushl number
pushl $printf_format
call printf
addl $8, %esp
movl $0, %eax
ret
Your example works fine, if you compile it with gcc -m32 example.s. If you use a GAS/LD-combination, you cannot terminate it with ret. Use instead:
pushl $0
call exit