adr@quiche.cs.mcgill.ca (Alain DURAND) (09/21/90)
Hello,
I've troubles with word alignments on different unix machine:
sizeof(struct foo) doesn't return the same thing on a sun3, sun386i
and sparc. Is there an option to set at compilation time or somewere
in the kernel to fix that?
thanks for any answer, please reply by E-Mail at:
adr@quiche.cs.mcgill.camikey@quiche.cs.mcgill.ca (Michael GALLOP) (09/25/90)
In article <4046@quiche.cs.mcgill.ca> adr@quiche.cs.mcgill.ca (Alain DURAND) writes: >Hello, > > I've troubles with word alignments on different unix machine: >sizeof(struct foo) doesn't return the same thing on a sun3, sun386i >and sparc. Is there an option to set at compilation time or somewere >in the kernel to fix that? >thanks for any answer, please reply by E-Mail at: > >adr@quiche.cs.mcgill.ca > Please note: The poster is only a grad student at Mcgill and does not reflect the undergrad education :-) Well Alain. There are several different factors. First off when dealing with any two machines, your request will likely return different values. One of the reasons-perhaps the main one- is the different architectures in the CPUs of the machines. From what I remember 80X86 swaps the bytes around from the way the SPARC deals with them More importantly is the difference in word size. An 80386 is a 32 bit machine -in some modes. In fact all of these are 32 bit machines. However the register addressing is different on each one. The Sparc uses circular addressing, whereas the i386 uses a form of virtual addressing. Also, an important factor is the overhead of your C compiler, your OS. These _MIGHT_ (probably won't) affect the result returned.... This, coupled with the different ways that each OS allocates memory will result in your observations. Why, though are you asking ? You can't magic number a (Not can't- shouldn't) malloc. So you should if ((malloc (sizeof (foo))==NULL) or whatever is needed. As for patching it in the kernel, I couldn't possibly see why, or how, you'd do that. By hard wiring a value like that in the kernel, you cause havoc in the rest of the OS. Especially in a 386. If you were to do that on a 386 in 386 protected mode, or, worse in virtual 8086 mode, the page frame would cause a memory fault- I should know, I spent many hours chasing my mistake on that one I tried to align with a magic number :-( -and dump the machine. -- | mikey@quiche.cs.mcgill.ca | Mike Gallop | |"Stealing from one author is plagarism....Stealing from many is research" | I shall walk through the valley of Death and I shall fear no evil....... ..Except, perhaps, a sadistics assignment
mikey@quiche.cs.mcgill.ca (Michael GALLOP) (09/25/90)
In article <4046@quiche.cs.mcgill.ca> adr@quiche.cs.mcgill.ca (Alain DURAND) writes: >Hello, > > I've troubles with word alignments on different unix machine: >sizeof(struct foo) doesn't return the same thing on a sun3, sun386i >and sparc. Is there an option to set at compilation time or somewere >in the kernel to fix that? >thanks for any answer, please reply by E-Mail at: > >adr@quiche.cs.mcgill.ca > Please note: The poster is only a grad student at Mcgill and does not reflect the undergrad education :- ) Well Alain. There are several different factors. First off when dealing with any two machines, your request will likely return different values. One of the reasons-perhaps the main one- is the different architectures in the CPUs of the machines. From what I remember 80X86 swaps the bytes around from the way the SPARC deals with them More importantly is the difference in word size. An 80386 is a 32 bit machine -in some modes. In fact all of these are 32 bit machines. However the register addressing is different on each one. The Sparc uses circular addressing, whereas the i386 uses a form of virtual addressing. Further, an important factor is the overhead of your C compiler, your OS. These _MIGHT_ ( probably won't) affect the result returned.... This, coupled with the different ways that each OS allocates memory will result in your observations. Why, though are you asking ? You can't magic number a (Not can't- shouldn't) malloc. So you should if ( ( malloc ( sizeof ( foo ) ) ==NULL ) or whatever is needed. As for patching it in the kernel, I couldn't possibly see why, or how, you'd do that. By hard wiring a value like that in the kernel, you cause havoc in the rest of the OS. Especially in a 386. If you were to do that on a 386 in 386 protected mode, or, worse in virtual 8086 mode, the page frame would cause a memory fault- I should know, I spent many hours chasing my mistake on that one I tried to align with a magic number :- ( -and dump the machine. -- | mikey@quiche.cs.mcgill.ca | Mike Gallop | |"Stealing from one author is plagarism....Stealing from many is research" | I shall walk through the valley of Death and I shall fear no evil....... ..Except, perhaps, a sadistics assignment