[Mono-dev] RVA Irregularities

[Kornél Pál]

Hi,

I don't know how ProcessModule.BaseAddress is implemented on Linux but 
you shouldn't use this.

If you want to look at the IL code open the file using FileStream or use 
Cecil.

Note that even if you modify IL code that would not affect code that is 
already compiled to native code.

Also note that RVA's are not required to be preserved when the image is 
loaded to memory.

Mono on Windows is using LoadLibrary in most cases that will map the 
image according to the RVAs but Linux has no support for PE files so 
images are just loaded without mapping PE sections to their designated 
virtual addresses.

Kornél

Nathan McCauley wrote:
> The following code excerpt from the attached C# program behaves 
> differently on Mono 2.0.1runtime for Windows and Mono 2.0.1 runtime on 
> the OpenSUSE VMWare image.  It contains a lookup of the base address 
> (contained in getBaseAddress()).  The loop should print the program's 
> Main() function IL code at runtime.  This RVA was found by looking it up 
> in ILDASM. 
> 
> The program was compiled the MS compiler.
> 
>    IntPtr baseAddr = getBaseAddress();
> 
>  for (int offset = 0x211c; offset < 0x2169; offset++)
>             {
>                     Console.WriteLine("Addr = {0:X}\tByte = {1:X}",
>                          baseAddr.ToInt32() + offset,
>              Marshal.ReadByte(new IntPtr(baseAddr.ToInt32() + offset)));
>             }
> 
> 
> 
> It seems like the loader is behaving differently on each platform.  Is 
> there something I should be doing to mitigate this behavior?
> 
> 
> Windows Mono Runtime output:
> Addr = 40211C   Byte = 13
> Addr = 40211D   Byte = 30
> Addr = 40211E   Byte = 4
> Addr = 40211F   Byte = 0
> Addr = 402120   Byte = 4B
> Addr = 402121   Byte = 0
> Addr = 402122   Byte = 0
> Addr = 402123   Byte = 0
> Addr = 402124   Byte = 2
> Addr = 402125   Byte = 0
> Addr = 402126   Byte = 0
> Addr = 402127   Byte = 11
> Addr = 402128   Byte = 28
> Addr = 402129   Byte = 1
> Addr = 40212A   Byte = 0
> Addr = 40212B   Byte = 0
> Addr = 40212C   Byte = 6
> Addr = 40212D   Byte = A
> Addr = 40212E   Byte = 20
> Addr = 40212F   Byte = 1C
> Addr = 402130   Byte = 21
> Addr = 402131   Byte = 0
> Addr = 402132   Byte = 0
> Addr = 402133   Byte = B
> Addr = 402134   Byte = 2B
> Addr = 402135   Byte = 34
> Addr = 402136   Byte = 72
> Addr = 402137   Byte = 69
> Addr = 402138   Byte = 0
> Addr = 402139   Byte = 0
> 
> Linux Mono Runtime output:
> Addr = B7DDB11C Byte = C
> Addr = B7DDB11D Byte = 2
> Addr = B7DDB11E Byte = 0
> Addr = B7DDB11F Byte = 0
> Addr = B7DDB120 Byte = 1
> Addr = B7DDB121 Byte = 0
> Addr = B7DDB122 Byte = 30
> Addr = B7DDB123 Byte = 0
> Addr = B7DDB124 Byte = 30
> Addr = B7DDB125 Byte = 0
> Addr = B7DDB126 Byte = 30
> Addr = B7DDB127 Byte = 0
> Addr = B7DDB128 Byte = 30
> Addr = B7DDB129 Byte = 0
> Addr = B7DDB12A Byte = 30
> Addr = B7DDB12B Byte = 0
> Addr = B7DDB12C Byte = 34
> Addr = B7DDB12D Byte = 0
> Addr = B7DDB12E Byte = 62
> Addr = B7DDB12F Byte = 0
> Addr = B7DDB130 Byte = 30
> Addr = B7DDB131 Byte = 0
> Addr = B7DDB132 Byte = 0
> Addr = B7DDB133 Byte = 0
> Addr = B7DDB134 Byte = 44
> Addr = B7DDB135 Byte = 0
> Addr = B7DDB136 Byte = E
> Addr = B7DDB137 Byte = 0
> Addr = B7DDB138 Byte = 1
> Addr = B7DDB139 Byte = 0
> 
> 
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