[llvm-bugs] [Bug 48677] New: [asan][win] Interceptor failures on Windows Insider builds

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=48677

            Bug ID: 48677
           Summary: [asan][win] Interceptor failures on Windows Insider
                    builds
           Product: compiler-rt
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: asan
          Assignee: unassignedbugs at nondot.org
          Reporter: dmajor at mozilla.com
                CC: hans at chromium.org, llvm-bugs at lists.llvm.org,
                    nicolasweber at gmx.de, rnk at google.com

In newer Windows Insider builds (20277 to 20231 at least), various system
functions are no longer preceded by sufficient `int 3` padding to insert a
hotpatch. 

This leads to two problems:

1. ASan falls back to using trampolines, which means it needs to scan through
more instructions than before, so it starts seeing encodings that
`GetInstructionSize()` doesn't know about.

That's easy enough to fix, but then...

2. The increased length of trampolines means a higher risk of clobbering a
branch target. In particular, a later part of `ntdll!strrchr` contains a jump
back to the +3 offset, which is now garbage.

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