does the loader changes the relocation table when it knows segmentation is off (noaways)?
let me try to explain my vague question.
A few days ago i started to learn about paging and segmentation, and I understood that today the segmentation is ignored by setting all the segments base to 0 and their max to the limit- 2^32 (also known as flat memory model).
But before that, and also today(altough ignored), each memory reference was combined of a segment register: segment offset. the segment register is a selector that contains an index to the segment in the segments table, which contains the base address of the segment. as I said before now its all 0. this memory reference is also known as "logical address".
From the way i see it, in the times where each segment had its own memory space, we would reach the first byte of code with: call CS:0 and the first byte of data with [DS:0].
But today it just would not work (i think), because all the segments uses the same memory space so the code needs to be different. foe Example, the first byte of code shoould be at (arbitrary address) call CS:0x4567 (just absolute and not an offset like before)
and the first data byte will be at (arbitrary address) [DS:0x12121212].
So it turns out that the same code should be a little bit different when it will be loaded to the ram with or without segmentation. so my question is, am I talking sense? if not please explain me the truth because all I mentioned are speculations. And if I am correct, does the loader do all this relocation magic (because it knows whether segmentation is on or off)? because in the way I see it, with segmentation on and off the code should be a little bit different from the reasons i mentioned above.
thank you, and have a nice day.
assembly memory-management linker operating-system
asked Nov 24 '18 at 11:08
ליאב לויליאב לוי
304
add a comment |
let me try to explain my vague question.
A few days ago i started to learn about paging and segmentation, and I understood that today the segmentation is ignored by setting all the segments base to 0 and their max to the limit- 2^32 (also known as flat memory model).
But before that, and also today(altough ignored), each memory reference was combined of a segment register: segment offset. the segment register is a selector that contains an index to the segment in the segments table, which contains the base address of the segment. as I said before now its all 0. this memory reference is also known as "logical address".
From the way i see it, in the times where each segment had its own memory space, we would reach the first byte of code with: call CS:0 and the first byte of data with [DS:0].
But today it just would not work (i think), because all the segments uses the same memory space so the code needs to be different. foe Example, the first byte of code shoould be at (arbitrary address) call CS:0x4567 (just absolute and not an offset like before)
and the first data byte will be at (arbitrary address) [DS:0x12121212].
So it turns out that the same code should be a little bit different when it will be loaded to the ram with or without segmentation. so my question is, am I talking sense? if not please explain me the truth because all I mentioned are speculations. And if I am correct, does the loader do all this relocation magic (because it knows whether segmentation is on or off)? because in the way I see it, with segmentation on and off the code should be a little bit different from the reasons i mentioned above.
thank you, and have a nice day.
assembly memory-management linker operating-system
asked Nov 24 '18 at 11:08
ליאב לויליאב לוי
304
can someone answer? :/
– ליאב לוי
Nov 24 '18 at 13:56
add a comment |
let me try to explain my vague question.
A few days ago i started to learn about paging and segmentation, and I understood that today the segmentation is ignored by setting all the segments base to 0 and their max to the limit- 2^32 (also known as flat memory model).
But before that, and also today(altough ignored), each memory reference was combined of a segment register: segment offset. the segment register is a selector that contains an index to the segment in the segments table, which contains the base address of the segment. as I said before now its all 0. this memory reference is also known as "logical address".
From the way i see it, in the times where each segment had its own memory space, we would reach the first byte of code with: call CS:0 and the first byte of data with [DS:0].
But today it just would not work (i think), because all the segments uses the same memory space so the code needs to be different. foe Example, the first byte of code shoould be at (arbitrary address) call CS:0x4567 (just absolute and not an offset like before)
and the first data byte will be at (arbitrary address) [DS:0x12121212].
So it turns out that the same code should be a little bit different when it will be loaded to the ram with or without segmentation. so my question is, am I talking sense? if not please explain me the truth because all I mentioned are speculations. And if I am correct, does the loader do all this relocation magic (because it knows whether segmentation is on or off)? because in the way I see it, with segmentation on and off the code should be a little bit different from the reasons i mentioned above.
thank you, and have a nice day.
assembly memory-management linker operating-system
asked Nov 24 '18 at 11:08
ליאב לויליאב לוי
304
let me try to explain my vague question.
A few days ago i started to learn about paging and segmentation, and I understood that today the segmentation is ignored by setting all the segments base to 0 and their max to the limit- 2^32 (also known as flat memory model).
But before that, and also today(altough ignored), each memory reference was combined of a segment register: segment offset. the segment register is a selector that contains an index to the segment in the segments table, which contains the base address of the segment. as I said before now its all 0. this memory reference is also known as "logical address".
From the way i see it, in the times where each segment had its own memory space, we would reach the first byte of code with: call CS:0 and the first byte of data with [DS:0].
But today it just would not work (i think), because all the segments uses the same memory space so the code needs to be different. foe Example, the first byte of code shoould be at (arbitrary address) call CS:0x4567 (just absolute and not an offset like before)
and the first data byte will be at (arbitrary address) [DS:0x12121212].
So it turns out that the same code should be a little bit different when it will be loaded to the ram with or without segmentation. so my question is, am I talking sense? if not please explain me the truth because all I mentioned are speculations. And if I am correct, does the loader do all this relocation magic (because it knows whether segmentation is on or off)? because in the way I see it, with segmentation on and off the code should be a little bit different from the reasons i mentioned above.
thank you, and have a nice day.
assembly memory-management linker operating-system
assembly memory-management linker operating-system
asked Nov 24 '18 at 11:08
ליאב לויליאב לוי
304
asked Nov 24 '18 at 11:08
ליאב לויליאב לוי
304
edited Nov 24 '18 at 15:54
ליאב לוי
asked Nov 24 '18 at 11:08
ליאב לויליאב לוי
304
asked Nov 24 '18 at 11:08
ליאב לויליאב לוי
304
asked Nov 24 '18 at 11:08
ליאב לויליאב לוי
304
304
can someone answer? :/
– ליאב לוי
Nov 24 '18 at 13:56
add a comment |
can someone answer? :/
– ליאב לוי
Nov 24 '18 at 13:56
can someone answer? :/
– ליאב לוי
Nov 24 '18 at 13:56
can someone answer? :/
– ליאב לוי
Nov 24 '18 at 13:56
add a comment |
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can someone answer? :/
– ליאב לוי
Nov 24 '18 at 13:56