fix: copy_file skip files larger than 1GB (Fixes #4039)

[IamHuskar]

Dotnet runtime may create 2TB memory-mapped files. 'copy_file' will persist this file.

[IamHuskar]

I'm not completely certain this is the correct fix, and English isn't my first language. Feel free to modify anything in this PR
@rocallahan @khuey

[rocallahan]

I think this fix should be in TraceWriter::write_mapped_region(), in copy_file_or_trace in particular. As I said in the linked issue, the code that starts if ((km.prot() & PROT_EXEC) tries to copy executable files into the trace for use by debuggers. But if the file is too big, then we shouldn't be doing this. We can check the size of km, we don't need to re-stat anything.

[IamHuskar]

I think this fix should be in TraceWriter::write_mapped_region(), in copy_file_or_trace in particular. As I said in the linked issue, the code that starts if ((km.prot() & PROT_EXEC) tries to copy executable files into the trace for use by debuggers. But if the file is too big, then we shouldn't be doing this. We can check the size of km, we don't need to re-stat anything.

I previously attempted to modify this part, but the size of km is not equal to the file size obtained through the fstat function call. I have already added a test case in the PR. Did I misunderstand something? I think I should place the file size check function in copy_file_or_trace, rather than inside the copy_file function.

[IamHuskar]

the CI test failed on ARM, but it works fine on my ARM device.

[rocallahan]

I previously attempted to modify this part, but the size of km is not equal to the file size obtained through the fstat function call. I have already added a test case in the PR. Did I misunderstand something? I think I should place the file size check function in copy_file_or_trace, rather than inside the copy_file function.

I see. Ok then, check the file size --- that makes sense, actually, since we're going to copy the whole file, and we don't want to copy too much.

But this check should still go next to the PROT_EXEC condition, because the goal here is "copy files when the mapping is PROT_EXEC, unless the file is too big".

[IamHuskar]

Why is the MAP_SHARED check placed after copy_file? Can we change the order of these if conditions?
If the km region is MAP_SHARED, src.setTrace will be executed, but at that point, the file copying has already been completed.