[llvm] [BOLT][Linux] Fix linux_banner lookup (PR #144962)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-bolt

Author: Maksim Panchenko (maksfb)

<details>
<summary>Changes</summary>

While detecting the Linux kernel version, look for `linux_banner` symbol with local visibility if the global one was not found.

Fixes #<!-- -->144847

---
Full diff: https://github.com/llvm/llvm-project/pull/144962.diff


2 Files Affected:

- (modified) bolt/lib/Rewrite/LinuxKernelRewriter.cpp (+25-17) 
- (modified) bolt/test/X86/linux-version.S (+11) 


``````````diff
diff --git a/bolt/lib/Rewrite/LinuxKernelRewriter.cpp b/bolt/lib/Rewrite/LinuxKernelRewriter.cpp
index 5a5e044184d0b..174721a3a0539 100644
--- a/bolt/lib/Rewrite/LinuxKernelRewriter.cpp
+++ b/bolt/lib/Rewrite/LinuxKernelRewriter.cpp
@@ -432,25 +432,33 @@ class LinuxKernelRewriter final : public MetadataRewriter {
 };
 
 Error LinuxKernelRewriter::detectLinuxKernelVersion() {
-  if (BinaryData *BD = BC.getBinaryDataByName("linux_banner")) {
-    const BinarySection &Section = BD->getSection();
-    const std::string S =
-        Section.getContents().substr(BD->getOffset(), BD->getSize()).str();
-
-    const std::regex Re(R"---(Linux version ((\d+)\.(\d+)(\.(\d+))?))---");
-    std::smatch Match;
-    if (std::regex_search(S, Match, Re)) {
-      const unsigned Major = std::stoi(Match[2].str());
-      const unsigned Minor = std::stoi(Match[3].str());
-      const unsigned Rev = Match[5].matched ? std::stoi(Match[5].str()) : 0;
-      LinuxKernelVersion = LKVersion(Major, Minor, Rev);
-      BC.outs() << "BOLT-INFO: Linux kernel version is " << Match[1].str()
-                << "\n";
-      return Error::success();
-    }
+  // Check for global and local linux_banner symbol.
+  BinaryData *BD = BC.getBinaryDataByName("linux_banner");
+  if (!BD)
+    BD = BC.getBinaryDataByName("linux_banner/1");
+
+  if (!BD)
+    return createStringError(errc::executable_format_error,
+                             "unable to locate linux_banner");
+
+  const BinarySection &Section = BD->getSection();
+  const std::string S =
+      Section.getContents().substr(BD->getOffset(), BD->getSize()).str();
+
+  const std::regex Re(R"---(Linux version ((\d+)\.(\d+)(\.(\d+))?))---");
+  std::smatch Match;
+  if (std::regex_search(S, Match, Re)) {
+    const unsigned Major = std::stoi(Match[2].str());
+    const unsigned Minor = std::stoi(Match[3].str());
+    const unsigned Rev = Match[5].matched ? std::stoi(Match[5].str()) : 0;
+    LinuxKernelVersion = LKVersion(Major, Minor, Rev);
+    BC.outs() << "BOLT-INFO: Linux kernel version is " << Match[1].str()
+              << "\n";
+    return Error::success();
   }
+
   return createStringError(errc::executable_format_error,
-                           "Linux kernel version is unknown");
+                           "Linux kernel version is unknown: " + S);
 }
 
 void LinuxKernelRewriter::processLKSections() {
diff --git a/bolt/test/X86/linux-version.S b/bolt/test/X86/linux-version.S
index e680d0d64a21f..a3d7f365304aa 100644
--- a/bolt/test/X86/linux-version.S
+++ b/bolt/test/X86/linux-version.S
@@ -17,6 +17,11 @@
 # RUN:   -Wl,--image-base=0xffffffff80000000,--no-dynamic-linker,--no-eh-frame-hdr
 # RUN: llvm-bolt %t.exe -o %t.out 2>&1 | FileCheck --check-prefix=CHECK-C %s
 
+# RUN: %clang -DD -target x86_64-unknown-unknown \
+# RUN:   %cflags -nostdlib %s -o %t.exe \
+# RUN:   -Wl,--image-base=0xffffffff80000000,--no-dynamic-linker,--no-eh-frame-hdr
+# RUN: llvm-bolt %t.exe -o %t.out 2>&1 | FileCheck --check-prefix=CHECK-D %s
+
   .text
   .globl foo
   .type foo, %function
@@ -46,6 +51,12 @@ linux_banner:
 #endif
 # CHECK-C: BOLT-INFO: Linux kernel version is 6.6
 
+#ifdef D
+  .hidden linux_banner
+  .string  "Linux version 6.6.15.2-2-xxx\n"
+#endif
+# CHECK-D: BOLT-INFO: Linux kernel version is 6.6
+
   .size  linux_banner, . - linux_banner
 
 ## Fake Linux Kernel sections.

``````````

</details>


https://github.com/llvm/llvm-project/pull/144962