[llvm] [BOLT] fix hugify for old krenels (#201813) (PR #201818)

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llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-bolt

Author: DmitriiMartynov

<details>
<summary>Changes</summary>

The PIE binary optimized with hugify option may crash on kernels below 5.10 due to unexpected segment alignment.

---
Full diff: https://github.com/llvm/llvm-project/pull/201818.diff


2 Files Affected:

- (modified) bolt/lib/Rewrite/RewriteInstance.cpp (+3-1) 
- (modified) bolt/test/runtime/hugify.c (+5) 


``````````diff
diff --git a/bolt/lib/Rewrite/RewriteInstance.cpp b/bolt/lib/Rewrite/RewriteInstance.cpp
index 9364e32939982..4b2f777000d50 100644
--- a/bolt/lib/Rewrite/RewriteInstance.cpp
+++ b/bolt/lib/Rewrite/RewriteInstance.cpp
@@ -705,6 +705,7 @@ Error RewriteInstance::discoverStorage(ELFObjectFile<ELFT> *ELFObjFile) {
 
   // Hugify: Additional huge page from left side due to
   // weird ASLR mapping addresses (4KB aligned)
+  // dm: no need for kernels 5.10 and above
   if (opts::Hugify && !BC->HasFixedLoadAddress) {
     NextAvailableAddress += BC->PageAlign;
   }
@@ -4251,9 +4252,10 @@ void RewriteInstance::mapCodeSections(BOLTLinker::SectionMapper MapSection) {
 
       // Hugify: Additional huge page from right side due to
       // weird ASLR mapping addresses (4KB aligned)
+      // dm: For kernels 5.10 and above alignment is enough
       if (opts::Hugify && !BC->HasFixedLoadAddress &&
           Section->getName() == LastNonColdSectionName)
-        Address = alignTo(Address, Section->getAlignment());
+        Address += BC->PageAlign;
     }
 
     // Make sure we allocate enough space for huge pages.
diff --git a/bolt/test/runtime/hugify.c b/bolt/test/runtime/hugify.c
index a4a718a1160df..ec234515351da 100644
--- a/bolt/test/runtime/hugify.c
+++ b/bolt/test/runtime/hugify.c
@@ -2,6 +2,11 @@
 
 #include <stdio.h>
 
+// For testing hugify on kernels below 5.10 without patch
+// "fs/binfmt_elf: use PT_LOAD p_align values for suitable start address"
+const char dummy_const_var_in_text[2 * 1024 * 1024 - 0x1000]
+    __attribute__((section(".text")));
+
 int main(int argc, char **argv) {
   printf("Hello world\n");
   return 0;

``````````

</details>


https://github.com/llvm/llvm-project/pull/201818