9 ms·

I wonder what makes AT&T assembly syntax "objectively crap".

colejohnson66 9y ago
You need to explicitly specify what the parameter sizes and types are. Plus, the parameters are backwards compared to Intel syntax: Intel: mov eax, 5 AT&T: movl $5, %eax In basically every C-like programming language, you assign 5 to eax with `eax=5` not `5=eax`. I can also tell that I'm working with the `long` variant of `mov` just by looking at the types involved. Intel's syntax for memory access seems more natural. If I don't want to add `ebx` to the address, I can leave it out; I can't in AT&T; I have to have this seemingly random comma. Plus, what's with the format? Intel: mov eax, [ds:eax*4+16] AT&T: movl ds:16(,%eax,4)
- ajross 9y ago
  Interestingly, in the language you actually wrote that complaint in: > you assign 5 to eax AT&T speaks English, basically. We move A to B. Destination goes last. Both seem sane enough. And in fact both get really balled up when you have three and four-argument instructions.
  - colejohnson66 9y ago
    I'll grant that, but it's a programming language, so I kind of expect it to follow the order assignment does when I write in C++, C#, etc.
    - ajross 9y ago
      AT&T assembly style significantly predates C++ (and C# by like two decades), and co-evolved with C. And strictly this isn't an assignment, anyway. Assignment is an abstract operation in a programming language. This is a machine instruction[1] for a physical machine, which does exactly one thing. [1] Pause while the peanut gallery points out that in fact there are like ninety six different instructions in x86 called some variant of "MOV". Yeah, yeah, we know.
      - i336_ 9y ago
        What. When did `mov` get 96 different instructions?
        chipaca 9y ago
        I think it's just a bit of hyperbole. I don't know enough of this to know whether http://c9x.me/x86/html/file_module_x86_id_176.html http://c9x.me/x86/html/file_module_x86_id_176.html is complete, but it gives you a sense of it all. (also https://www.cl.cam.ac.uk/~sd601/papers/mov.pdf https://www.cl.cam.ac.uk/~sd601/papers/mov.pdf if you haven't seen it)
        i336_ 9y ago
        Huh, interesting. Apparently there are 35 rows in the table at http://www.felixcloutier.com/x86/MOV.html http://www.felixcloutier.com/x86/MOV.html (according to Chrome and `$0.childElementCount`). I only discovered gcc.godbolt.org links to documentation via context menu just the other day! Regarding the PDF... ouch. Wonder if any executable obfuscators have tried that approach :P (and I also wonder what sort of overhead it has.)
    - kbenson 9y ago
      > I kind of expect it to follow the order assignment does when I write in C++, C#, etc. There is no special precedence that should be applied to C. Similarity to C only imparts benefits to those that are fimilar with C-like languages or variants that follow that structure. That ends up being a lot of people because of how popular C and variants have been, but that's doesn't inherently make it better. It's sort of a pet peeve of mine when people point out differences from C as problems without any objective facts to back up whether it actually is more or less useful in some aspects. If we never stood up to that type of thinking, we'd all by much poorer in the programming language department.
      - hyperpape 9y ago
        This does raise the question: which languages other than AT&T assembly put the value first?
        AstralStorm 9y ago
        AT&T syntax puts the operator first, not the value. AT&T is Verb Subject Object. Intel is alien Verb Object Subject. Many kinds of S expressions result in similar code. That would mean Lisp derivatives.
        tom_mellior 9y ago
        > AT&T syntax puts the operator first, not the value. If "operator" has any meaning in assembly language, it would have to refer to the opcode. Both variants have the opcode (mov/movl) first. > AT&T is Verb Subject Object. Intel is alien Verb Object Subject. Both "move 5 into EAX" and "move into EAX the value 5" are imperatives. Neither of them has a subject, or more precisely, the subject is omitted (https://en.wikipedia.org/wiki/Imperative_mood https://en.wikipedia.org/wiki/Imperative_mood). In both of these, 5 is an object. "into EAX" is an adverbial phrase or something. It's true that one sounds more alien than the other when forcibly translated to English. Then again, assembly language is not English, so that's neither here nor there.
        hyperpape 9y ago
- throwaway-1209 9y ago
  Makes you wonder why not write it as e.g. "eax mov 5" or even "eax = 5".
  - tom_mellior 9y ago
    I've seen assembly languages that do separate target and source operands with an = sign. So you would write that something like: mov eax = 5 and use a similar style for other things, like: add eax = ebx, ecx This is very nice and clear. But it only really works for three-address assembly languages, i.e., where the target register may be different from the sources. In classical x86, the target of an add is identical to one of the operands. So you would need something like add eax += ebx or add eax = eax, ebx where you must duplicate a register. Presumably when these assembly languages were developed 40 years ago, this was perceived as too much syntax.
    - Koshkin 9y ago
      > nice and clear Looks absolutely horrible to me, why not simply eax = ebx + ecx ?
      - throwaway-1209 9y ago
        +1. Make it look more like a severely restricted version of C.
      - tom_mellior 9y ago
        I guess because there's no simple infix operator for every operation implemented by the machine. Also, the addition may be floating-point or 32, 16, or 8 bit, signed or unsigned, possibly vectorized. An opcode is a good place to express these things.
        throwaway-1209 9y ago
        Opcodes are fine, no one is saying everything has to be expressed as an operator. I'd like to see more of a C/C++ intrinsics syntax, but with total control over the order of instructions and register allocation. Basically same power as assembly, syntax close to intrinsics, but you tell it which registers to use, and there's one instruction per line, and they're executed exactly as you write them, with no creativity on the part of the compiler.
- rdtsc 9y ago
  Right, but the mnemonic reads better in AT&T then "move 5 to register eax" and Intel seems backwards.
  - spc476 9y ago
    It's what you get used to. I'm used to x86 being "dst,src". It never bothered me that on the Motorola 68000 it went "src,dst" as, it was what it was. Intel defined it one way, Motorola another way [1]. My gripe with AT&T style (and it's called AT&T because K&R wrote their assembler that way) is that it uses sigils to mark registers (something I've never seen any other assembler do) and specifically broke with the manufacturer's mnemonics. Yes, I can see why they did it that way (a consistent format for assembly across multiple architectures) but I don't necessarily agree with it (Go's assembler has gone father by not even bothering with the register names the manufacturer uses). Almost forgot---another annoying aspect of AT&T is the use of "$" to designate an immediate value. Every assembler I used (prior to my exposure to Unix) used "#" for immediate value, and "$" for hexadecimal. But noooo, AT&T had to use "$" for immediate, and "0x" to designate hexadecimal and thus, I hit a brick wall each time I read code in AT&T format. [1] Also interesting to note---Intel is little endian, Motorola is bigendian.
    - rdtsc 9y ago
      I learned on Intel and that's the only I can use. Just pointing out that reading the expression makes more sense in AT&T style so might be why they did it that way. And always wondered why the need for % in AT&T for registers. It seems like there would no ambiguity based on instruction.
- meditationapp 9y ago
  Why would you expect assignment order to be similar? Nothing else about c syntax is shared. If anything, at&t follows English: move literal 5 into register eax.
dboreham 9y ago
Wow. Literally a 40 year old thread!
- Taniwha 9y ago
  well not quite, but slightly more than 30 years - you point is right - those who don't read history are doomed to repeat it
TheCondor 9y ago
I thought gas did both...
- colejohnson66 9y ago
  It does, now, but it used to not.
codys 9y ago
All the intel docs use intel syntax, and for some instructions converting between the 2 syntax forms isn't immediately obvious.
- sigjuice 9y ago
  I wish there was a version of Intel's docs with AT&T syntax.
bgrainger 9y ago
The best set of arguments I've seen against it: http://x86asm.net/articles/what-i-dislike-about-gas/ http://x86asm.net/articles/what-i-dislike-about-gas/

You need to explicitly specify what the parameter sizes and types are. Plus, the parameters are backwards compared to Intel syntax: Intel: mov eax, 5 AT&T: movl $5, %eax In basically every C-like programming language, you assign 5 to eax with `eax=5` not `5=eax`. I can also tell that I'm working with the `long` variant of `mov` just by looking at the types involved. Intel's syntax for memory access seems more natural. If I don't want to add `ebx` to the address, I can leave it out; I can't in AT&T; I have to have this seemingly random comma. Plus, what's with the format? Intel: mov eax, [ds:eax*4+16] AT&T: movl ds:16(,%eax,4)

ajross 9y ago
Interestingly, in the language you actually wrote that complaint in: > you assign 5 to eax AT&T speaks English, basically. We move A to B. Destination goes last. Both seem sane enough. And in fact both get really balled up when you have three and four-argument instructions.
- colejohnson66 9y ago
  I'll grant that, but it's a programming language, so I kind of expect it to follow the order assignment does when I write in C++, C#, etc.
  - ajross 9y ago
    AT&T assembly style significantly predates C++ (and C# by like two decades), and co-evolved with C. And strictly this isn't an assignment, anyway. Assignment is an abstract operation in a programming language. This is a machine instruction[1] for a physical machine, which does exactly one thing. [1] Pause while the peanut gallery points out that in fact there are like ninety six different instructions in x86 called some variant of "MOV". Yeah, yeah, we know.
    - i336_ 9y ago
      What. When did `mov` get 96 different instructions?
      - chipaca 9y ago
        I think it's just a bit of hyperbole. I don't know enough of this to know whether http://c9x.me/x86/html/file_module_x86_id_176.html http://c9x.me/x86/html/file_module_x86_id_176.html is complete, but it gives you a sense of it all. (also https://www.cl.cam.ac.uk/~sd601/papers/mov.pdf https://www.cl.cam.ac.uk/~sd601/papers/mov.pdf if you haven't seen it)
        i336_ 9y ago
        Huh, interesting. Apparently there are 35 rows in the table at http://www.felixcloutier.com/x86/MOV.html http://www.felixcloutier.com/x86/MOV.html (according to Chrome and `$0.childElementCount`). I only discovered gcc.godbolt.org links to documentation via context menu just the other day! Regarding the PDF... ouch. Wonder if any executable obfuscators have tried that approach :P (and I also wonder what sort of overhead it has.)
  - kbenson 9y ago
    > I kind of expect it to follow the order assignment does when I write in C++, C#, etc. There is no special precedence that should be applied to C. Similarity to C only imparts benefits to those that are fimilar with C-like languages or variants that follow that structure. That ends up being a lot of people because of how popular C and variants have been, but that's doesn't inherently make it better. It's sort of a pet peeve of mine when people point out differences from C as problems without any objective facts to back up whether it actually is more or less useful in some aspects. If we never stood up to that type of thinking, we'd all by much poorer in the programming language department.
    - hyperpape 9y ago
      This does raise the question: which languages other than AT&T assembly put the value first?
      - AstralStorm 9y ago
        AT&T syntax puts the operator first, not the value. AT&T is Verb Subject Object. Intel is alien Verb Object Subject. Many kinds of S expressions result in similar code. That would mean Lisp derivatives.
        tom_mellior 9y ago
        > AT&T syntax puts the operator first, not the value. If "operator" has any meaning in assembly language, it would have to refer to the opcode. Both variants have the opcode (mov/movl) first. > AT&T is Verb Subject Object. Intel is alien Verb Object Subject. Both "move 5 into EAX" and "move into EAX the value 5" are imperatives. Neither of them has a subject, or more precisely, the subject is omitted (https://en.wikipedia.org/wiki/Imperative_mood https://en.wikipedia.org/wiki/Imperative_mood). In both of these, 5 is an object. "into EAX" is an adverbial phrase or something. It's true that one sounds more alien than the other when forcibly translated to English. Then again, assembly language is not English, so that's neither here nor there.
        hyperpape 9y ago
throwaway-1209 9y ago
Makes you wonder why not write it as e.g. "eax mov 5" or even "eax = 5".
- tom_mellior 9y ago
  I've seen assembly languages that do separate target and source operands with an = sign. So you would write that something like: mov eax = 5 and use a similar style for other things, like: add eax = ebx, ecx This is very nice and clear. But it only really works for three-address assembly languages, i.e., where the target register may be different from the sources. In classical x86, the target of an add is identical to one of the operands. So you would need something like add eax += ebx or add eax = eax, ebx where you must duplicate a register. Presumably when these assembly languages were developed 40 years ago, this was perceived as too much syntax.
  - Koshkin 9y ago
    > nice and clear Looks absolutely horrible to me, why not simply eax = ebx + ecx ?
    - throwaway-1209 9y ago
      +1. Make it look more like a severely restricted version of C.
    - tom_mellior 9y ago
      I guess because there's no simple infix operator for every operation implemented by the machine. Also, the addition may be floating-point or 32, 16, or 8 bit, signed or unsigned, possibly vectorized. An opcode is a good place to express these things.
      - throwaway-1209 9y ago
        Opcodes are fine, no one is saying everything has to be expressed as an operator. I'd like to see more of a C/C++ intrinsics syntax, but with total control over the order of instructions and register allocation. Basically same power as assembly, syntax close to intrinsics, but you tell it which registers to use, and there's one instruction per line, and they're executed exactly as you write them, with no creativity on the part of the compiler.
rdtsc 9y ago
Right, but the mnemonic reads better in AT&T then "move 5 to register eax" and Intel seems backwards.
- spc476 9y ago
  It's what you get used to. I'm used to x86 being "dst,src". It never bothered me that on the Motorola 68000 it went "src,dst" as, it was what it was. Intel defined it one way, Motorola another way [1]. My gripe with AT&T style (and it's called AT&T because K&R wrote their assembler that way) is that it uses sigils to mark registers (something I've never seen any other assembler do) and specifically broke with the manufacturer's mnemonics. Yes, I can see why they did it that way (a consistent format for assembly across multiple architectures) but I don't necessarily agree with it (Go's assembler has gone father by not even bothering with the register names the manufacturer uses). Almost forgot---another annoying aspect of AT&T is the use of "$" to designate an immediate value. Every assembler I used (prior to my exposure to Unix) used "#" for immediate value, and "$" for hexadecimal. But noooo, AT&T had to use "$" for immediate, and "0x" to designate hexadecimal and thus, I hit a brick wall each time I read code in AT&T format. [1] Also interesting to note---Intel is little endian, Motorola is bigendian.
  - rdtsc 9y ago
    I learned on Intel and that's the only I can use. Just pointing out that reading the expression makes more sense in AT&T style so might be why they did it that way. And always wondered why the need for % in AT&T for registers. It seems like there would no ambiguity based on instruction.
meditationapp 9y ago
Why would you expect assignment order to be similar? Nothing else about c syntax is shared. If anything, at&t follows English: move literal 5 into register eax.

dboreham 9y ago

Wow. Literally a 40 year old thread!

Taniwha 9y ago
well not quite, but slightly more than 30 years - you point is right - those who don't read history are doomed to repeat it

TheCondor 9y ago

I thought gas did both...

colejohnson66 9y ago
It does, now, but it used to not.

codys 9y ago

All the intel docs use intel syntax, and for some instructions converting between the 2 syntax forms isn't immediately obvious.

sigjuice 9y ago
I wish there was a version of Intel's docs with AT&T syntax.

bgrainger 9y ago

The best set of arguments I've seen against it: http://x86asm.net/articles/what-i-dislike-about-gas/ http://x86asm.net/articles/what-i-dislike-about-gas/