Re: A Famous Security Bug

On Mon, 25 Mar 2024 13:26:01 +0100
David Brown <david.brown@hesbynett.no> wrote:

On 25/03/2024 12:16, Michael S wrote:

On Sun, 24 Mar 2024 23:43:32 +0100
David Brown <david.brown@hesbynett.no> wrote: 

>
I could be  wrong here, of course.
 

 
It seems, you are.
 

 
It happens - and it was not unexpected here, as I said.  I don't have
all these compilers installed to test.
 
But it would be helpful if you had a /little/ more information.  If
you don't know why some compilers generate binaries that have memory
mapped at 0x400000, and others do not, fair enough.  I am curious,
but it's not at all important.
 

I am not an expert, but it does not look like the problem is directly
related to compiler or linker. All 32-bit Windows compilers/linkers,
including gcc, clang and MSVC, by default put symbol ___ImageBase at
address 4 MB. However loader relocates it to wherever it wants,
typically much higher.
I don't know for sure why loader does it to images generated by gcc,
clang and MSVC and does not do it to images generated by lccwin and
others, but I have an educated guess: most likely, these other compilers
link by default with an option similar to Microsoft's /Fixed
https://learn.microsoft.com/en-us/cpp/build/reference/fixed-fixed-base-address?view=msvc-170

The option disables ASLR and thus can shorten app load time and make
performance just a little snappier. Still, I wouldn't make it default.

To get similar behavior with [32-bit] MSVC user can specify '/linker
/fixed' on the command line. I don't know how to do it with gcc variant
supplied with msys2. But, I'd guess, if you google for long enough, you
can find it.