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Search found 302 results on 13 pages for 'assembler'.

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• GNU ld removes section

  - by Jonatan

  I'm writing a boot script for an ARM-Cortex M3 based device. If I compile the assembler boot script and the C application code and then combine the object files and transfer them to my device everything works. However, if I use ar to create an archive (libboot.a) and combine that archive with the C application there is a problem: I've put the boot code in a section: .section .boot, "ax" .global _start _start: .word 0x10000800 /* Initial stack pointer (FIXME!) */ .word start .word nmi_handler .word hard_fault_handler ... etc ... I've found that ld strips this from the final binary (the section "boot" is not available). This is quite natural as there is no dependency on it that ld knows about, but it causes the device to not boot correctly. So my question is: what is the best way to force this code to be included?

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• Getting memory section information

  - by Basilevs

  Can somebody explain me how the following code works? # if defined(__ELF__) # define __SECTION_FLAGS ", \"aw\" , @progbits" /* writable flag needed for ld ".[cd]tors" sections bug workaround) */ # elif defined(__COFF__) # define __SECTION_FLAGS ", \"dr\"" /* untested, may be writable flag needed */ # endif asm ( ".section .ctors" __SECTION_FLAGS "\n" ".globl __ctors_begin__\n" "__ctors_begin__:\n" ".previous\n" ); asm /* ld ".[cd]tors" sections bug workaround */ ( ".section .ctors0" __SECTION_FLAGS "\n" ".globl __ctors0_begin__\n" "__ctors0_begin__:\n" ".previous\n" ); Similarly we are getting __ctors_end__ , __ctors0_end__ and destructors location is also obtained this way. After some ld bug workarounds all functions pointed by pointers from __ctors_begin__ to __ctors_end__ are executed. I don't know assembler and this code is impossible for me to interpret. BTW: I know that invoking C++ contructors/destructors from C is not a task to be considered safe or easy.

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• What does subl do here?

  - by drozzy

  So... I'm compiling into assembler, with gcc -S -O2 -m32: void h(int y){int x; x=y+1; f(y); f(2); } And it gives me the following: .file "sample.c" .text .p2align 4,,15 .globl h .type h, @function h: pushl %ebp movl %esp, %ebp subl $24, %esp movl 8(%ebp), %eax movl %eax, (%esp) call f movl $2, 8(%ebp) leave jmp f .size h, .-h .ident "GCC: (GNU) 4.4.3 20100127 (Red Hat 4.4.3-4)" .section .note.GNU-stack,"",@progbits Now I know what pushl and movel: they store the current frame pointer onto the stack and then set the value of the frame pointer register to the value of the Stack Pointer. But I have no idea what the subl $24, %esp is. Thanks!

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• n++ vs n=n+1. Which one is faster

  - by piemesons

  Somebody asked me Is n++ faster than n=n+1? My answer:-- ++ is a unary operator in C which(n++) takes only one machine instruction to execute while n=n+1 takes more than one machine instructions to execute. Anyone correct me if I am wrong, but in Assembler it take something like this: n++: inc n n = n + 1; mov ax n add ax 1 mov n ax its not exactli this, but it's near it.but in most cases a good compiler will change n = n + 1 to ++n.So A good compiler will generate same code for both and hence the same time to execute.

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• 80x86 16-bit asm: lea cx, [cx*8+cx] causes error on NASM (compiling .com file)

  - by larz

  Title says it all. The error NASM gives (dispite my working OS) is "invalid effective address". Now i've seen many examples of how to use LEA and i think i gots it right but yet my NASM dislikes it. I tried "lea cx, [cx+9]" and it worked; "lea cx, [bx+cx]" didn't. Now if i extended my registers to 32-bits (i.e. "lea ecx, [ecx*8+ecx]") everything would be well but i am restricted to use 16- and 8-bit registers only. Is here anyone so knoweledgeable who could explain me WHY my assembler doesn't let me use lea the way i supposed it should be used? Thanks.

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• Great projects, works, people in intersection of programming and art/music?

  - by jacob

  In a recent question I was introduced to the work of André Michelle, which blew me away. What other great people or works do you know in the fields of art and music? As someone with a love for math/programming and art/music I'd love to know more about people using sophisticated (or not so sophisticated) techniques to produce creative things. The software used can be anything from Max/MSP, Flash to simple C code or Assembler. Pointers to forums, blogs, newsletters and similar are very appreciated as well.

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• Using the "naked" attribute for functions in GCC

  - by Art Spasky

  GCC documentation (http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html) states in 6.29 Declaring Attributes of Functions "naked Use this attribute on the ARM, AVR, IP2K, RX and SPU ports to indicate that the specified function does not need prologue/epilogue sequences generated by the compiler. It is up to the programmer to provide these sequences. The only statements that can be safely included in naked functions are asm statements that do not have operands. All other statements, including declarations of local variables, if statements, and so forth, should be avoided. Naked functions should be used to implement the body of an assembly function, while allowing the compiler to construct the requisite function declaration for the assembler." Can I safely call functions using C syntax from naked functions, or only by using asm?

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• How to specify execution time of x86 and PowerPC instructions?

  - by Goofy

  Hello! I have to approximate execution time of PowerPC and x86 assembler code.I understand that I cannot compute exact it dependson many problems (current processor state - x86 processor dicides internal instructions in microinstructions, memory access time obtainig code from cache of from slower memory etc.). I found some information in Intel Optimizaction reference (APPENDIX C), but it does not provide information about all general purpose instructions. Is there any complete reference about it? What about PowerPC processors? Where can I fund such information?

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• Lablgtk2 Installation on Windows.

  - by Animesh

  Hi there people, I am currently relearning Ocaml and am in the need of a good editor. There is a new editor from OcamlForge: OCamlEditor http://ocamleditor.forge.ocamlcore.org/. Prerequisite for installation is Lablgtk2. Installing Lablgtk2 on windows is not straight forward and there is good instruction here: http://wwwfun.kurims.kyoto-u.ac.jp/soft/lsl/install-win32.txt I have completed the first two steps and in the third step, as warned, it is failing on the native code version. This is where I am left stranded. How do I check to see if the assembler is on my path? What am I missing here? Please help me move forward from this point. Sincere thanks. Animesh

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• C++ word to bytes

  - by Vit

  Hi, I tried to read CPUID using assembler in C++. I know there is function for it in , but I want the asm way. So, after CPUID is executed, it should fill eax,ebx,ecx registers with ASCII coded string. But my problem is, since I can in asm adress only full, or half eax register, how to break that 32 bits into 4 bytes. I used this: #include <iostream> #include <stdlib.h> int main() { _asm { cpuid /*There I need to mov values from eax,ebx and ecx to some propriate variables*/ } system("PAUSE"); return(0); }

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• Is there a technical way to speed up a general program above current PC speed limit?

  - by Maksee

  Let's imagine I developed a Windows console application implementing some algorithm calculating something. Let's say it doesn't use any threads, just straightforward linear approach with ifs, loops and so on. Is there any technical way to make if run it 100x times faster than on the most advanced current PC? For example one of the way would be to run it on a super computer that emulates i386 faster than any of the existing PCs. But in this case the question what computer and does it really have ability to emulate Windows. In other words, is there real examples of such approach? Although in general it looks useless, but if there is a way, one could develop some program on his general home computer and pay for running it much faster on some other hardware. I suppose that this question could be asked on superuser.com, but since there are possible specific with such things as assembler instructions or threads, I thought that stackoverflow.com is better

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• Interrupt On GAS

  - by Nathan Campos

  I'm trying to convert my simple program from Intel syntax to the AT&T(to compile it with GAS). I've successfully converted a big part of my application, but I'm still getting an error with the int(the interrupts). My function is like this: printf: mov $0x0e, %ah mov $0x07, %bl nextchar: lodsb or %al, %al jz return int 10 jmp nextchar return: ret msg db "Welcome To Track!", 0Ah But when I compile it, I got this: hello.S: Assembler messages: hello.S:13: Error: operand size mismatch for int' hello.S:19: Error: no such instruction:msg db "Hello, World!",0Ah' What I need to do?

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• Software Protection: Shuffeling my application?

  - by Martijn Courteaux

  Hi, I want to continue on my previous question: http://stackoverflow.com/questions/3007168/torrents-can-i-protect-my-software-by-sending-wrong-bytes Developer Art suggested to add a unique key to the application, to identifier the cracker. But JAB said that crackers can search where my unique key is located by checking for binary differences, if the cracker has multiple copies of my software. Then crackers change that key to make them self anonymous. That is true. Now comes the question: If I want to add a unique key, are there tools to shuffle (a kind of obfuscation) the program modules? So, that a binary compare would say that the two files are completely different. So they can't locate the identifier key. I'm pretty sure it is possible (maybe by replacing assembler blocks and make some jumps). I think it would be enough to make 30 to 40 shuffles of my software. Thanks

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• How to make columns as wide as the widest entry?

  - by Helper Method

  For a gcc cheatsheet I'm writing, I want to create a table which should describe how gcc interprets different file endings. The table I created so far is defined as follows: |====================================================================== |.c |C source code which must be preprocessed. |.i |C source code which should not be preprocessed. |.h |C header file to be turned into a precompiled header. |.s |Assembler code. |other | An object file to be fed straight into linking. Any file name with no recognized suffix is treated this way. |====================================================================== The problem I have is that the table spans the total page width, but what I want is that each column only is as wide as it's widest entry, and that the table will span only as much witdh as it needs.

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• JMP instruction in Flex/bison

  - by Imran

  Hallo everybody, Can someone help me out of my situation, im searching for a instrucior that implements the JMP (Jump) instructior like in Assembler. I've found out that it could be withe the goto function of Flex/Bison but i have no really idea how to do. Have got anyone idea. Im very grateful of yours help. Thanks. Here is an example how it looks like. with the JMP instructor, he goes to the label L1. :L1 IF FLAG AND X"0001" EVT 23; ELSE WAIT 500 ms; JMP L1; END IF;

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• Why Aren't Programs Written In Assembly More Often?

  - by mudge

  It seems to be a mainstream opinion that assembly programming takes longer and is more difficult to program in than a higher level language such as C. Therefore it seems to be recommend or assumed that it is better to write in a higher level language for these reasons and for the reason of better portability. Recently I've been writing in x86 assembly and it has dawned on me that perhaps these reasons are not really true, except perhaps portability. Perhaps it is more of a matter of familiarity and knowing how to write assembly well. I also noticed that programming in assembly is quite different than programming in an HLL. Perhaps a good and experienced assembly programmer could write programs just as easily and as quickly as an experienced C programmer writing in C. Perhaps it is because assembly programming is quite different than HLLs, and so requires different thinking, methods and ways, which makes it seem very awkward to program in for the unfamiliar, and so gives it its bad name for writing programs in. If portability isn't an issue, then really, what would C have over a good assembler such as NASM?

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• How can I truncate the mangled C++ identifiers shown by GDB's disassemble command?

  - by Rhys Ulerich

  GDB's disassemble command is nice for short C identifiers, e.g. main. For long, mangled C++ identifiers the verbosity is overkill. For example, using icpc I see results like (gdb) disassemble 0x49de2f 0x49de5b Dump of assembler code from 0x49de2f to 0x49de5b: 0x000000000049de2f <_ZN5pecos8suzerain16fftw_multi_array6detail18c2c_buffer_processIPA2_dPKSt7complexIdEilNS2_26complex_copy_differentiateIS4_EEEEvT_T1_T2_T0_SD_SE_RKT3_+167>: mov 0x18(%rsp),%rsi Displays that long are annoying in the CLI. They make GDB's TUI assembly display all but useless. Is there a way to tell GDB to show a truncated identifier? Say clip all but 50 characters?

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• Are there still completely new programming languages and -paradigms to be born?

  - by llasa

  Are there still completely new programming languages and -paradigms (which will actually go mainstream and still be used decades after their appearance) to be born? What I'm talking about are groundbreaking things like the rise of object oriented programming, C++, or PHP. With new programming languages I mean that they actually are completely different from what you know, as different as when you set a guy who used assembler for a decade, and even programmed some kind of 3D game in it, in front of something as high-level as PHP, Ruby or Python? Which new paradigms and programming languages are there to come? What could be different about them? Who will possibly create them and how fast will they rise?

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• What platforms have something other than 8-bit char?

  - by Craig McQueen

  Every now and then, someone on SO points out that char (aka 'byte') isn't necessarily 8 bits. It seems that 8-bit char is almost universal. I would have thought that for mainstream platforms, it is necessary to have an 8-bit char to ensure its viability in the marketplace. Both now and historically, what platforms use a char that is not 8 bits, and why would they differ from the "normal" 8 bits? When writing code, and thinking about cross-platform support (e.g. for general-use libraries), what sort of consideration is it worth giving to platforms with non-8-bit char? In the past I've come across some Analog Devices DSPs for which char is 16 bits. DSPs are a bit of a niche architecture I suppose. (Then again, at the time hand-coded assembler easily beat what the available C compilers could do, so I didn't really get much experience with C on that platform.)

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• Working with QWords

  - by Glenn1234

  I'm learning and in the course of that working on an assembler conversion which uses QWORDs a lot (x86-32bit). Now my reference material doesn't have anything on working with such values beyond the obvious of splitting them up into the 32-bit registers. I guess they're on the old side. The newer processors have mmx and sse instructions and the like. Would I be served well to look into those instructions for solving this? What is the best way to handle doing work on QWORD values?

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• Dynamically create labels in gas macros?

  - by pgod

  Hi everyone, I would like to dynamically create a set of labels in an assembly function using a gas macro. I would like to do something like this: .macro set_up_jumptab_entry prefix, from=0, to=10 .quad \prefix_\item .if \to-\from set_up_jumptab_entry \prefix,"(\from+1)",\to .endif .endm set_up_jumptab_entry myfunc 0 10 Here \prefix_\item would be something like myfunction_7. Now, I can find lots of examples of recursive invocation, but I haven't found one of just label concatenation involving passed-in macro arguments. Gas is quite poorly documented, so answering this question is difficult for me. Can you concatenate arguments to macros with other tokens to make single tokens? What's your favorite gas assembler reference?

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• A general question about compilation and interpretation.

  - by wucnuc

  Hi stackoverflow, I apologize in advance for the possible stupidity of this question. However, the following has been the source of some confusion for me and I know the people here will be able to handily clear up the confusion for me. Basically, I would like to finally understand the relationship between any and all of the following terms. Some of the terms I do actually understand pretty well, but some of them are similar in my mind and I would like to once and for all to see their relationships/distinctions laid out all at once. They are: compiler interpreter bytecode machine code assembler assembly language binary object code executable Ideally, an answer would use examples from Java and C++ and other well-known programming languages that a young-ish student like me would be familiar with. Also, if you want to throw in any other useful terms that would be fine too :)

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• What segments does C compiled program use?

  - by b-gen-jack-o-neill

  Hi, I read on OSDev wiki, that protected mode of x86 architecture allow you to create separate segments for code and data, while you cannot write into code section. That Windows (yes, this is the platform) loads new code into code segment, and data are created on data segment. But, if this is the case, how does program know it must switch segments to the data segment? Becouse if I understand it right, all adress instructions point to the segment you run the code from, unless you switch the descriptor. But I also read, that so colled flat memory model allows you to run code and data within one segment. But I read this only in connection to assembler. So, please, what is the case with C compiled code on Windows? Thanks.

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• How to find the jmp address during a x86 function call?

  - by Bruce

  Suppose we have a call foo statement. So when the assembler encounters a call statement it breaks it down into - push ip + 6 jmp <addr of foo> I have the return address in a register ebx. Now I want to find out the "addr of foo". How do I do it? I want to confirm that the push statement is present before the jmp. Will the memory map look something like this? ------- push (what will be the value stored in this byte?? opcode ??) ------- jmp (what will be the value stored in this byte?? opcode ??) ------- jmp byte 1 ------- jmp byte 2 ------- jmp byte 3 ------- jmp byte 4 ------- return address stored in ebx ------- What are the opcodes for push and jmp?

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• Quick CPU ring mode protection question

  - by b-gen-jack-o-neill

  Hi, me again :) I am very curious in messing up with HW. But my top level "messing" so far was linked or inline assembler in C program. If my understanding of CPU and ring mode is right, I cannot directly from user mode app access some low level CPU features, like disabling interrupts, or changing protected mode segments, so I must use system calls to do everything I want. But, if I am right, drivers can run in ring mode 0. I actually don´t know much about drivers, but this is what I ask for. I just want to know, is learning how to write your own drivers and than call them the way I should go, to do what I wrote? I know I could write whole new OS (at least to some point), but what I exactly want to do is acessing some low level features of HW from standart windows application. So, is driver the way to go?

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