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> Note that my tutorial uses the AT&T assembly language syntax instead of Intel syntax. This makes me curious: how widely used is the AT&T syntax these days? I

> Note that my tutorial uses the AT&T assembly language syntax instead of Intel syntax. This makes me curious: how widely used is the AT&T syntax these days? I could easily be wrong, but my impression was that most work is done in the Intel syntax. This may be ignorance on my part, as the Intel syntax is all I've ever used on Intel processors. I've coded in a dozen other assembly languages for various processors, but Intel chips seem to be the only ones with two different assembly language syntaxes, right down to the source/destination order.

muststopmyths 6y ago
gdb and lldb's default disassembly syntax is AT&T, so I'd say it's pretty widespread.
lokedhs 6y ago
The M68k has two different syntaxes too. The argument order is still the same (src,dest, the correct order in my opinion), but other things are different, with the main difference being indirect addressing which is (a0) in Motorola syntax, while it's a0@ in AT&T syntax. So while the changes might not be as huge, it's definitely not just Intel.
- masklinn 6y ago
  > The argument order is still the same (src,dest, the correct order in my opinion) OTOH dest, src matches every assignment ever, and is much more regular when extending to multi-parameter mnemonics (e.g. madd).
  - colejohnson66 6y ago
    I’m going to ignore the characters such as % and $, and also the parameter order (sortove) There’s also the fact that the Intel and AMD x86 manuals list them as MNEMONIC dst, src1 GAS does this: MNEMONIC src1, dst Which is fine, but what about 3 and 4 operand instructions? I always have to look that up. 8087 FPU instructions also (in GAS), due to a historical quirk, are in “Intel” form: MNEMONIC dst, src Then there’s that whole indirect syntax of: segment:displacement(base,index,scale) Whereas “Intel” syntax is much clearer: segment:[base + index*scale + displacement] This leads to weird things like: [ebx*2+10] ; I can see what that’s doing 10(,%ebx,2) ; I need to remember what the order is and convert it in my head I’m not trying to convince anyone here. If you like “AT&T” syntax, that’s fine with me. I just prefer “Intel” syntax because of these reasons.
retrac 6y ago
It's still the same division as always. Linux and other UNIXes on x86 and x86_64 generally use AT&T syntax. The rest of the x86 world uses Intel syntax. And of course *nix has always been a minority on x86. > I've coded in a dozen other assembly languages for various processors, but Intel chips seem to be the only ones with two different assembly language syntaxes, It's a historical quirk. Generally, today if there is a widely used and accepted assembler syntax targeting the architecture, UNIX porters would use that assembler's syntax. GAS accepts normal ARM style syntax, for example. But that's today. x86 is ancient. And so is UNIX on the x86. Going all the way back to the late 1970s, the 8086 was one of the first microprocessors that could host a decent UNIX environment. The rush was on as soon as the chip was released. (Most of the porting fervour would shift to the 68000 about 18 months later when that came out.) There was no established assembler aside from the one from Intel. MASM wouldn't be written for another couple years. UNIX at this point already had a full quasi-portable toolchain, which of course was familiar to the porters. And they planned to live in an all-UNIX world anyway. The only assembly anyone would ever write would, hopefully, be a dozen lines in the kernel. So they just adapted what they had and what worked. The old PDP-11 UNIX assembler, backwards syntax and prefixes and all. And here we are 40 years later.
jart 6y ago
AT&T syntax is best syntax. Linux, GCC, LLVM, etc. all use it. Scott Wolchok writes it in a style that's more verbose than it needs to be. It's probably a good call since this is an educational blog post. Like there's some nuance to when you need things like q on statements `movq %rdi,8(%rsp)`. For example, this is fine: `mov %rdi,8(%rsp)` but you need it if you move an immediate to memory, e.g. `movq $123,8(%rsp)`. I like to avoid them because mnemonics like `orb` don't appear to the untrained eye as the `or` instruction! The GNU-style suffixes can also appear multiple times within an instruction name in various combinations, e.g. pclmullqlqdq vs. pclmulhqhqdq.
- swolchok 6y ago
  > Scott Wolchok writes it I didn’t write it, I just copied the compiler output from Godbolt so that the article could be read on mobile, where Godbolt’s UI doesn’t work so well and switching tabs back and forth is difficult.

muststopmyths 6y ago

gdb and lldb's default disassembly syntax is AT&T, so I'd say it's pretty widespread.

lokedhs 6y ago

The M68k has two different syntaxes too. The argument order is still the same (src,dest, the correct order in my opinion), but other things are different, with the main difference being indirect addressing which is (a0) in Motorola syntax, while it's a0@ in AT&T syntax. So while the changes might not be as huge, it's definitely not just Intel.

masklinn 6y ago
> The argument order is still the same (src,dest, the correct order in my opinion) OTOH dest, src matches every assignment ever, and is much more regular when extending to multi-parameter mnemonics (e.g. madd).
- colejohnson66 6y ago
  I’m going to ignore the characters such as % and $, and also the parameter order (sortove) There’s also the fact that the Intel and AMD x86 manuals list them as MNEMONIC dst, src1 GAS does this: MNEMONIC src1, dst Which is fine, but what about 3 and 4 operand instructions? I always have to look that up. 8087 FPU instructions also (in GAS), due to a historical quirk, are in “Intel” form: MNEMONIC dst, src Then there’s that whole indirect syntax of: segment:displacement(base,index,scale) Whereas “Intel” syntax is much clearer: segment:[base + index*scale + displacement] This leads to weird things like: [ebx*2+10] ; I can see what that’s doing 10(,%ebx,2) ; I need to remember what the order is and convert it in my head I’m not trying to convince anyone here. If you like “AT&T” syntax, that’s fine with me. I just prefer “Intel” syntax because of these reasons.

retrac 6y ago

It's still the same division as always. Linux and other UNIXes on x86 and x86_64 generally use AT&T syntax. The rest of the x86 world uses Intel syntax. And of course *nix has always been a minority on x86. > I've coded in a dozen other assembly languages for various processors, but Intel chips seem to be the only ones with two different assembly language syntaxes, It's a historical quirk. Generally, today if there is a widely used and accepted assembler syntax targeting the architecture, UNIX porters would use that assembler's syntax. GAS accepts normal ARM style syntax, for example. But that's today. x86 is ancient. And so is UNIX on the x86. Going all the way back to the late 1970s, the 8086 was one of the first microprocessors that could host a decent UNIX environment. The rush was on as soon as the chip was released. (Most of the porting fervour would shift to the 68000 about 18 months later when that came out.) There was no established assembler aside from the one from Intel. MASM wouldn't be written for another couple years. UNIX at this point already had a full quasi-portable toolchain, which of course was familiar to the porters. And they planned to live in an all-UNIX world anyway. The only assembly anyone would ever write would, hopefully, be a dozen lines in the kernel. So they just adapted what they had and what worked. The old PDP-11 UNIX assembler, backwards syntax and prefixes and all. And here we are 40 years later.

jart 6y ago

AT&T syntax is best syntax. Linux, GCC, LLVM, etc. all use it. Scott Wolchok writes it in a style that's more verbose than it needs to be. It's probably a good call since this is an educational blog post. Like there's some nuance to when you need things like q on statements `movq %rdi,8(%rsp)`. For example, this is fine: `mov %rdi,8(%rsp)` but you need it if you move an immediate to memory, e.g. `movq $123,8(%rsp)`. I like to avoid them because mnemonics like `orb` don't appear to the untrained eye as the `or` instruction! The GNU-style suffixes can also appear multiple times within an instruction name in various combinations, e.g. pclmullqlqdq vs. pclmulhqhqdq.

swolchok 6y ago
> Scott Wolchok writes it I didn’t write it, I just copied the compiler output from Godbolt so that the article could be read on mobile, where Godbolt’s UI doesn’t work so well and switching tabs back and forth is difficult.