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revolution 13 Feb 2009, 11:11
I get no problems on my XP box with that.
Curiously, Olly does not know what the flag means, it just displays "20" and leaves it at that. |
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13 Feb 2009, 11:11 |
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revolution 13 Feb 2009, 13:23
I've done some searching around and found a number of applications that always use this flag. It seems that there is no downside to doing this. If you boot in 3GB mode then the flag is used, if you boot normally then the flag is ignored.
Although, not all versions of Windows support 3GB mode so if your app requires a large memory space then just putting this switch won't help you unless the user has also configured the OS for it. |
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13 Feb 2009, 13:23 |
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Tomasz Grysztar 13 Feb 2009, 13:37
Well, I think it won't do any harm to have this flag always on.
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13 Feb 2009, 13:37 |
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asmfan 13 Feb 2009, 14:55
Tomasz Grysztar wrote: Well, I think it won't do any harm to have this flag always on. It is harm! Think how much use jg instead of ja in their 32bit apps. That will be run under x64 with 4GiB of memory. The flas should be set on demand the same way like format PE... L_A_Aware or shorter just aware in header. _________________ Any offers? |
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13 Feb 2009, 14:55 |
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Tomasz Grysztar 13 Feb 2009, 15:00
Well, I was not aware of people using JG when comparing addresses.
But that's some point. |
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13 Feb 2009, 15:00 |
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revolution 13 Feb 2009, 15:27
Nobody needs to compare addresses like that. Windows still allocates memory at 0x7FFxxxxx for itself so it is not like you get a contiguous block of RAM to use that straddles the boundary to 0x80000000. You have to allocate separate regions to be able to use the high RAM. Doing an address comparison across different regions would not really make sense.
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13 Feb 2009, 15:27 |
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sinsi 13 Feb 2009, 22:10
Pushing the Limits of Windows: Virtual Memory
Quote: Since the high bit of a pointer referencing an address below 2GB is always zero, they would use the high bit in their pointers as a flag for their own data, clearing it of course before referencing the data. If they ran with a 3GB address space they would inadvertently truncate pointers that have values greater than 2GB, causing program errors including possible data corruption. So if you write your own code, you should be OK. Quote: That will be run under x64 with 4GiB of memory. 32-bit apps still only have 4G of addresses, so DLLs and stuff still get loaded below 4G - you could have 16TiB of RAM, but your 32-bit app still has a 32-bit address space. |
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13 Feb 2009, 22:10 |
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revolution 14 Feb 2009, 01:57
I have some code that uses spare bits in an address pointer to store data. But I've never used the high bits. The low bits (usually the lower two) are always zero for pointers to dword aligned structures and dword data. A simple masking can extract the lower data bits and/or the higher address bits.
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14 Feb 2009, 01:57 |
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asmfan 14 Feb 2009, 09:30
[q]32-bit apps still only have 4G of addresses, so DLLs and stuff still get loaded below 4G - you could have 16TiB of RAM, but your 32-bit app still has a 32-bit address space.[/q]
yes you are right. [q]That will be run under x64 with 4GiB of memory.[/q] it was about virtual memory availability to 32bit UM app. |
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14 Feb 2009, 09:30 |
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sinsi 14 Feb 2009, 09:48
OK, but 32-bit apps work exactly the same under 64-bit windows, no matter where the actual 4KiB page comes from, but the app can only address 4Gib of address space.
I can't think of a time I've used 'jg' instead of 'ja' - signed dwords are (for me) a pain in the arse... |
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14 Feb 2009, 09:48 |
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asmfan 14 Feb 2009, 13:06
4KiB, 2MiB or 1GiB pages.
Anyway this flag sould be set with caution to unsigned vs signed arithmetic with addresses. Good that you write right code, then you can set this flag for sure. |
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14 Feb 2009, 13:06 |
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Alphonso 14 Feb 2009, 18:48
So I guess as there is a very small chance it might cause problems it would be best to leave it as it is (not enabled) and those who code such that its not a problem could easily modify the package themselves to use it. Does that sound about right?
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14 Feb 2009, 18:48 |
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LocoDelAssembly 14 Feb 2009, 18:57
Would it be too cumbersome to add a new directive or perhaps a new option to the assembler? Something like "format pe [gui|console] [version] [dll] [at address] [on file] [large]" (perhaps I'm missing some components but I think you can get the idea
) |
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14 Feb 2009, 18:57 |
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Alphonso 15 Feb 2009, 11:00
Do you mean something like this...
LAE= Large Address Enabled ??? Code: ;TABLES.INC . . symbols_3: ;3 character symbols . . db 'gui',1Bh,2 db 'lae',1Bh,82h ;<-- add LAE symbol, is 82h free/okay? db 'mm0',10h,0B0h . . Code: ;FORMATS.INC . . pe_settings: . . cmp al,80h je dll_flag cmp al,81h je wdm_flag cmp al,82h ;<-- check for LAE je lae_flag ; jmp pe_settings . . wdm_flag: bts [format_flags],9 jc setting_already_specified jmp pe_settings lae_flag: ;<-- bts [format_flags],13 ;is bit 13 free/okay ? jc setting_already_specified ; jmp pe_settings subsystem_setting: . . mov dword [edx+14h],0E0h ; size of optional header mov dword [edx+16h],10B010Eh; flags and magic value mov eax,[format_flags] ;<-- and eax, 1 shl 13 ; ugly code by or byte [edx+16h],ah ; alphonso the butcher ! mov eax,[image_base] ; . . PS don't be surprised if the above code breaks something or does not work.
EDIT : Forgot to add, use as for example Code: format PE GUI 4.0 LAE
entry start
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. Last edited by Alphonso on 15 Feb 2009, 11:05; edited 1 time in total |
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15 Feb 2009, 11:00 |
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revolution 15 Feb 2009, 11:04
Alphonso: Good job. I like it when people are prepared to look into the source to see how things work.
One thing we need to convince Tomasz of is to use symbolic constants. |
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15 Feb 2009, 11:04 |
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LocoDelAssembly 15 Feb 2009, 15:15
Yep, good one Alphonso.
Thanks  |
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15 Feb 2009, 15:15 |
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Tomasz Grysztar 19 Feb 2009, 10:37
revolution wrote: If you boot in 3GB mode then the flag is used, if you boot normally then the flag is ignored. The flag appears also to be used in WoW64 - well, it seemed quite obvious. And in WoW64 your application may actually get to use the whole 4 GB space, not only 3 GB. So you have any suggestions for the name of the flag? Maybe something like "largeaddr"? |
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19 Feb 2009, 10:37 |
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Alphonso 21 Feb 2009, 10:42
Judging by the responses it looks as if its going to be left up to you Tomasz
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21 Feb 2009, 10:42 |
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revolution 21 Feb 2009, 14:46
The name is not really important. So sure, that suggestion is fine.
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21 Feb 2009, 14:46 |
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