basic(possibly insane) question about compilers.

[theju112]

i don't know if this question is valid or not.tried on google but i didnt get a solution.

does a compiler generate different machine codes for different cpus?
like does it generate different binary codes for intel and amd for the same program?

if so how does the compiler know what cpu the computer has?

then does a compiler generate different codes for different operating systems?

[Salem]

> does a compiler generate different machine codes for different cpus?
Yes.

> like does it generate different binary codes for intel and amd for the same program?
Possibly.
GCC for example will generate default code which will run on anything better than a 386.
Or you can have one of any number of machine specific flags which will generate more optimal code for a particular CPU variant.

> if so how does the compiler know what cpu the computer has?
You read the box the compiler came in (or the web page) to see what target(s) it supports.

> then does a compiler generate different codes for different operating systems?
The compiler probably doesn't care about your OS.

All the OS magic is usually hidden inside say libc, where the actual OS specific API's (say to open a file) reside.
To that end (creating an image that will run on a particular OS) is really a linker issue, not a compiler issue.

[laserlight]

i don't know if this question is valid or not.tried on google but i didnt get a solution.

does a compiler generate different machine codes for different cpus?

I tried on google and got a few links that looked like they might answer the question. Granted, they did not appear to answer the question directly, but it is pretty easy to infer the answer. (Like, if an alien wanted to know whether every country in the world used US dollar as the primary medium of exchange and after searching found a currency converter tool online, the alien would infer that there are currencies besides the US dollar, even though the currency converter did not provide an FAQ that explicitly stated this.)

I think you need to be more persistent with your searching. Just because there is no FAQ with your exact question does not mean that you should immediately turn to this forum for help with the excuse that you tried to search but failed.

[CommonTater]

This is complicated... The answer is...

It depends on the compiler.

Cross-platform compilers will generate different code for different CPUs and different code again for different OSs.... But you have to tell it which. It can't possibly know at run time so it's up to the end user to select software that is compatible with their CPU/OS...

For Windows...
On 32 bit OSs Intel and AMD both run on the same x86 instruction sets. That was the AMD's whole idea... to make an Intel compatible CPU and they went right out and did it better than Intel.

On 64 bit Windows there are 2 code sets... IA64 whitch is specific to the Itanium processor from Intel and X64 (aka amd64) which is for both Intel and AMD 64 bit processors.

GENERALLY (as in there are exceptions)... Code produced by 16 bit compilers (Turbo C, some early GCC versions, etc) will not run on a 64 bit OS; windows will tell you it's not a valid PE image. 32 bit x86 code will run on both Intel and AMD in both 32 and 64 bit OSs, but this may not always be the case. 64bit x64 code only runs on 64 bit Intel and AMD systems and most compilers will not create 64 bit code on 32 bit systems because there would be no way to test it. 64 bit IA64 code only runs on 64 bit Itanium based server systems.

[theju112]

I tried on google and got a few links that looked like they might answer the question. Granted, they did not appear to answer the question directly, but it is pretty easy to infer the answer. (Like, if an alien wanted to know whether every country in the world used US dollar as the primary medium of exchange and after searching found a currency converter tool online, the alien would infer that there are currencies besides the US dollar, even though the currency converter did not provide an FAQ that explicitly stated this.)

I think you need to be more persistent with your searching. Just because there is no FAQ with your exact question does not mean that you should immediately turn to this forum for help with the excuse that you tried to search but failed.

so you think im an alien(just joking).i know my all my posts sound like out of this world.it'll be that way till i am thrown out of here.

seriously i searched a lot...just wanted to save some time and wanted to be sure. will be careful next time.

All the OS magic is usually hidden inside say libc, where the actual OS specific API's (say to open a file) reside.
To that end (creating an image that will run on a particular OS) is really a linker issue, not a compiler issue.

thanks salem.i had read that libc contains library routines and headers but i didnt know apis would be in there. im not so familiar with APIs, all i know is that an api is used for performing specific functions on behalf of the programmer.

but your answer explains enough.

[CommonTater]

so you think im an alien(just joking).i know my all my posts sound like out of this world.it'll be that way till i am thrown out of here.

Welcome to my ignore list...

[Maz]

I tried on google and got a few links that looked like they might answer the question. Granted, they did not appear to answer the question directly, but it is pretty easy to infer the answer. (Like, if an alien wanted to know whether every country in the world used US dollar as the primary medium of exchange and after searching found a currency converter tool online, the alien would infer that there are currencies besides the US dollar, even though the currency converter did not provide an FAQ that explicitly stated this.)

I think you need to be more persistent with your searching. Just because there is no FAQ with your exact question does not mean that you should immediately turn to this forum for help with the excuse that you tried to search but failed.

??? What on earth are you babbling Laser? Last time I checked in here, you were helpfull guy with posts containing knowledge that benefit the readers.

For me the original post appeared to be a valid question, related to C and containing greatly more interesting things to consider than the "snprintf's returnvalue may vary depending the operating system, and thus you should always handle both the negative and positive (larger than given buffer size) return values" - posts. Furthermore, now when Salem did answer to this question, this thread does benefit reader. It contains now some valuable information, which is much harder to find than the "thou shall not use void main, thou shall not use gets, ..." type of advieces these forums tend to be flooded with.

Aliens and currencies... For god's sake, couldn't you have used the time writing that took to produce something constructive instead?

[theju112]

This is complicated...

so is your answer. i am not ready for all this sir.
this is the first time im hearing IA64.
2 code sets in windows?is this something related to cisc and risc?

[hqt]

Sorry, when I learned assembler, I found that no one use assembler to write driver because each assembler just comparable with some type of processor (for example: you need an assembler A to write program for AMD and assembler B to write program for INTEL), they always write driver on some high language, (maybe the most is C) --->so my answer is: when you write a program, when compile it, each processor will have different binary code.

And how about different OS, I think obvious that different(and very different too @@)( except language like java that I don't know). for example, when you write on C on Windows, C will use some API functions of windows and if you use C on Linux, of course C will use other function--> so binary code will be different.

I have read somewhere, they tell that, slogan of java is "write once, run anywhere",It seems that binary code of two different OS are same!!! (but every java program, they run on "Java virtual machine", so maybe, this thing make two programs different

all information above maybe.... very wrong :">

[AndrewHunter]

i don't know if this question is valid or not.tried on google but i didnt get a solution.

does a compiler generate different machine codes for different cpus?
like does it generate different binary codes for intel and amd for the same program?

if so how does the compiler know what cpu the computer has?

then does a compiler generate different codes for different operating systems?

For future reference, posts such as these belong in the Tech Board. As for your questions, you are going to need to understand the difference between compilation and linking. Additionally, you are going to want to look at Instruction Set Architecture (ISA) and the ELF and PE file formats.

After reading through this information, you should be able to ask more informed questions, and hopefully have the required knowledge to narrow your search terms to prevent not being able to find the answer by yourself.

[theju112]

??? What on earth are you babbling Laser? Last time I checked in here, you were helpfull guy with posts containing knowledge that benefit the readers.

thanks for that maz . but youll probably change your mind if you read my other posts.

but as you pointed out i asked the question because i had a difficult time searching for the answer.

[AndrewHunter]

??? What on earth are you babbling Laser? Last time I checked in here, you were helpfull guy with posts containing knowledge that benefit the readers.

I don't know who you are, but your post was neither informative, funny, or even the slightest bit justified.

[BUNCH OF NONSENSE].....
all information above maybe.... very wrong :">

All the information is wrong and should be ignored. Please check your facts more thoroughly before posting replies.

[theju112]

Welcome to my ignore list...

please please wait wait wait......i am just fooling around.

please continue posting answers.

though we always end up on the wrong sides,i value your answers.

if you still want to add me to your ignore list,im helpless.

[CommonTater]

Sorry, when I learned assembler, I found that no one use assembler to write driver because each assembler just comparable with some type of processor (for example: you need an assembler A to write program for AMD and assembler B to write program for INTEL), they always write driver on some high language, (maybe the most is C) --->so my answer is: when you write a program, when compile it, each processor will have different binary code.

Not actually true... on 32 bit code, both Intel and AMD run the same basic x86 instruction sets and their code is interchangeable. Assemblers like MASM and POASM see no difference between them.

On 64 bit code you have two instruction sets... IA64 and x64 (aka amd64)... IA64 is specific to the Intel Itanium server chip... x64 code will run equally well on both Intel and AMD processors, provided the OS is compiled as 64 bit code.

Windows 64 bit versions run x86 code through an emulator (stupidly named WOW64) but do not run 16 bit IAPX code at all.

And how about different OS, I think obvious that different(and very different too @@)( except language like java that I don't know). for example, when you write on C on Windows, C will use some API functions of windows and if you use C on Linux, of course C will use other function--> so binary code will be different.

I have read somewhere, they tell that, slogan of java is "write once, run anywhere",It seems that binary code of two different OS are same!!! (but every java program, they run on "Java virtual machine", so maybe, this thing make two programs different

all information above maybe.... very wrong :">

The Java run time environment is OS specific... the token code interpreted by the runtime is not.

[hqt]

All the information is wrong and should be ignored. Please check your facts more thoroughly before posting replies.

ah I don't joke anything or tell something just for funny. but after some my stupid post about pointer, I see that I may... very stupid, so I don't trust information that I have learnt by myself