[compiler-rt] [hwasan] Don't check code model if there are no real globals (PR #131152)

[Thurston Dang via llvm-commits]

https://github.com/thurstond updated https://github.com/llvm/llvm-project/pull/131152

>From 7ee3d2e808b2e89f6628138e03c4db8a1b8b7fa3 Mon Sep 17 00:00:00 2001
From: Thurston Dang <thurston at google.com>
Date: Thu, 13 Mar 2025 14:55:47 +0000
Subject: [PATCH 1/2] [hwasan] Don't check code model if there are no real
 globals

Currently, the code model check is always performed even if there are no real globals, because the HWASan compiler pass always leaves a note. This unnecessarily adds a 2**32 byte size limit.

This patch elides the check if the globals note doesn't actually contain globals, thus allowing larger libraries to be successfully instrumented without globals.

Sent from my iPhone
---
 compiler-rt/lib/hwasan/hwasan_globals.cpp | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/compiler-rt/lib/hwasan/hwasan_globals.cpp b/compiler-rt/lib/hwasan/hwasan_globals.cpp
index 7e0f3df20dd05..6663a8f0e82c4 100644
--- a/compiler-rt/lib/hwasan/hwasan_globals.cpp
+++ b/compiler-rt/lib/hwasan/hwasan_globals.cpp
@@ -73,16 +73,21 @@ ArrayRef<const hwasan_global> HwasanGlobalsFor(ElfW(Addr) base,
         continue;
       }
 
-      // Only libraries with instrumented globals need to be checked against the
-      // code model since they use relocations that aren't checked at link time.
-      CheckCodeModel(base, phdr, phnum);
-
       auto *global_note = reinterpret_cast<const hwasan_global_note *>(desc);
       auto *globals_begin = reinterpret_cast<const hwasan_global *>(
           note + global_note->begin_relptr);
       auto *globals_end = reinterpret_cast<const hwasan_global *>(
           note + global_note->end_relptr);
 
+      // Only libraries with instrumented globals need to be checked against the
+      // code model since they use relocations that aren't checked at link time.
+      //
+      // There is always a HWASan globals note ("Create the note even if we
+      // aren't instrumenting globals. - HWAddressSanitizer.cpp), but we can
+      // elide the code model check if there are no real globals.
+      if (globals_begin != globals_end)
+        CheckCodeModel(base, phdr, phnum);
+
       return {globals_begin, globals_end};
     }
   }

>From 7b3b1490c39a3d7f4776b17ea60a558f6976be0c Mon Sep 17 00:00:00 2001
From: Thurston Dang <thurston at google.com>
Date: Thu, 13 Mar 2025 15:01:58 +0000
Subject: [PATCH 2/2] Formatting

---
 compiler-rt/lib/hwasan/hwasan_globals.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler-rt/lib/hwasan/hwasan_globals.cpp b/compiler-rt/lib/hwasan/hwasan_globals.cpp
index 6663a8f0e82c4..e2723450e26ec 100644
--- a/compiler-rt/lib/hwasan/hwasan_globals.cpp
+++ b/compiler-rt/lib/hwasan/hwasan_globals.cpp
@@ -83,7 +83,7 @@ ArrayRef<const hwasan_global> HwasanGlobalsFor(ElfW(Addr) base,
       // code model since they use relocations that aren't checked at link time.
       //
       // There is always a HWASan globals note ("Create the note even if we
-      // aren't instrumenting globals. - HWAddressSanitizer.cpp), but we can
+      // aren't instrumenting globals." - HWAddressSanitizer.cpp), but we can
       // elide the code model check if there are no real globals.
       if (globals_begin != globals_end)
         CheckCodeModel(base, phdr, phnum);