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

[via llvm-commits]

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

>From 97e6791030b93b4157d6dfda56049bf55750a754 Mon Sep 17 00:00:00 2001
From: Dmitrii Martynov <martynovdmitryvladimirovich at yandex.ru>
Date: Fri, 5 Jun 2026 13:03:50 +0300
Subject: [PATCH] [BOLT] fix hugify for old krenels (#201813)

The PIE binary optimized with hugify option may crash on kernels
below 5.10 due to unexpected segment alignment.
---
 bolt/lib/Rewrite/RewriteInstance.cpp | 4 +++-
 bolt/test/runtime/hugify.c           | 5 +++++
 2 files changed, 8 insertions(+), 1 deletion(-)

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;