[NFC][sanitizer] Add checks for impossible state

[vitalybuka]

Before it was touched here afec953.

Important assumption that the stack is descending, but I don't think we
support ascending stack anyware.

[llvmbot]

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: Vitaly Buka (vitalybuka)

Changes

I don't have reproducers, and don't know if this
branch is even possible but it looks like a typo
in 031c40d.

Before the patch:
For order "stk_begin, tls_begin, stk_end, tls_end", range [stk_end, tls_end) was discarded.
For order "stk_begin, tls_begin, tls_end, stk_end", range [stk_end, stk_end) was discarded.

After the patch:
For order "stk_begin, tls_begin, stk_end, tls_end", range [stk_end, tls_end) goes to tls.
For order "stk_begin, tls_begin, tls_end, stk_end", range [stk_end, stk_end) goes to tls.

---

Full diff: https://github.com/llvm/llvm-project/pull/108672.diff

1 Files Affected:

• (modified) compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp (+1-1)

diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp
index c3c717bbdbe4c9..579d163479858c 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp
@@ -642,7 +642,7 @@ void GetThreadStackAndTls(bool main, uptr *stk_addr, uptr *stk_size,
   if (!main) {
     // If stack and tls intersect, make them non-intersecting.
     if (*tls_addr > *stk_addr && *tls_addr < *stk_addr + *stk_size) {
-      if (*stk_addr + *stk_size < *tls_addr + *tls_size)
+      if (*stk_addr + *stk_size > *tls_addr + *tls_size)
         *tls_size = *stk_addr + *stk_size - *tls_addr;
       *stk_size = *tls_addr - *stk_addr;
     }

[MaskRay]

I believe the intention was:

Before the patch:
"stk_begin, tls_begin, stk_end, tls_end": range [stk_end, tls_end) was discarded.

However, the case is invalid and impossible. If stk_begin<tls_begin<stk_end, the tls range must be a subrange of [stk_begin,stk_end).

After the patch:
"stk_begin, tls_begin, stk_end, tls_end": range [stk_end, tls_end) goes to tls.

I think this is a no-op.

"stk_begin, tls_begin, tls_end, stk_end": range [stk_end, stk_end) goes to tls.

This extension effect isn't needed.

---

I think we can remove this statement.

[vitalybuka]

I think we can remove this statement.

More aggressive checks

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[fmayer]

Important assumption that the stack is descending, but I don't think we
support ascending stack anyware.

Put this into a comment.