Dont internalize extern definitions and add proper section info

Author: altugbozkurt07

src/llvm/mod.rs

@@ -16,10 +16,11 @@ use llvm_sys::{
     LLVMAttributeFunctionIndex, LLVMLinkage, LLVMVisibility,
     bit_reader::LLVMParseBitcodeInContext2,
     core::{
-        LLVMCreateMemoryBufferWithMemoryRange, LLVMDisposeMemoryBuffer, LLVMDisposeMessage,
-        LLVMGetEnumAttributeKindForName, LLVMGetMDString, LLVMGetModuleInlineAsm, LLVMGetTarget,
-        LLVMGetValueName2, LLVMRemoveEnumAttributeAtIndex, LLVMSetLinkage, LLVMSetModuleInlineAsm2,
-        LLVMSetVisibility,
+        LLVMCountBasicBlocks, LLVMCreateMemoryBufferWithMemoryRange, LLVMDisposeMemoryBuffer,
+        LLVMDisposeMessage, LLVMGetEnumAttributeKindForName, LLVMGetMDString,
+        LLVMGetModuleInlineAsm, LLVMGetTarget, LLVMGetValueName2, LLVMIsAFunction,
+        LLVMIsAGlobalVariable, LLVMIsDeclaration, LLVMRemoveEnumAttributeAtIndex, LLVMSetLinkage,
+        LLVMSetModuleInlineAsm2, LLVMSetSection, LLVMSetVisibility,
     },
     error::{
         LLVMDisposeErrorMessage, LLVMGetErrorMessage, LLVMGetErrorTypeId, LLVMGetStringErrorTypeId,
@@ -41,6 +42,7 @@ use llvm_sys::{
         LLVMCreatePassBuilderOptions, LLVMDisposePassBuilderOptions, LLVMRunPasses,
     },
 };
+use log::info;
 use tracing::{debug, error};
 pub(crate) use types::{
     context::{InstalledDiagnosticHandler, LLVMContext},
@@ -261,6 +263,28 @@ pub(crate) fn internalize(
     export_symbols: &HashSet<Cow<'_, [u8]>>,
 ) {
     if !name.starts_with(b"llvm.") && !export_symbols.contains(name) {
+        if unsafe { !LLVMIsAFunction(value).is_null() } {
+            let num_blocks = unsafe { LLVMCountBasicBlocks(value) };
+            if num_blocks == 0 {
+                unsafe { LLVMSetSection(value, c".ksyms".as_ptr()) };
+                info!(
+                    "not internalizing undefined function {}",
+                    str::from_utf8(name).unwrap_or("<invalid utf8>")
+                );
+                return;
+            }
+        }
+        if unsafe { !LLVMIsAGlobalVariable(value).is_null() } {
+            if unsafe { LLVMIsDeclaration(value) != 0 } {
+                unsafe { LLVMSetSection(value, c".ksyms".as_ptr()) };
+                info!(
+                    "not internalizing undefined global variable {}",
+                    str::from_utf8(name).unwrap_or("<invalid utf8>")
+                );
+                return;
+            }
+        }
+
         unsafe { LLVMSetLinkage(value, LLVMLinkage::LLVMInternalLinkage) };
         unsafe { LLVMSetVisibility(value, LLVMVisibility::LLVMDefaultVisibility) };
     }

tests/assembly/extern_linkage.rs

@@ -0,0 +1,43 @@
+// assembly-output: bpf-linker
+// compile-flags: --crate-type cdylib -C link-arg=--emit=llvm-ir
+
+#![no_std]
+
+// aux-build: loop-panic-handler.rs
+extern crate loop_panic_handler;
+
+// Extern declarations
+extern "C" {
+    fn bpf_kfunc_call_test_acquire(arg: *mut u64) -> *mut u64;
+    fn bpf_kfunc_call_test_release(arg: *mut u64);
+    static bpf_prog_active: u32;
+    static CONFIG_HZ: u64;
+}
+
+#[no_mangle]
+#[link_section = "tc"]
+pub fn test_extern_symbols() -> u64 {
+    unsafe {
+        let mut val: u64 = 42;
+        let ptr = bpf_kfunc_call_test_acquire(&mut val as *mut u64);
+        bpf_kfunc_call_test_release(ptr);
+        
+        let active = core::ptr::read_volatile(&bpf_prog_active);
+        let hz = core::ptr::read_volatile(&CONFIG_HZ);
+        active as u64 + hz
+    }
+}
+
+
+// Verify extern variables: external, not internal
+// CHECK: @bpf_prog_active = external{{.*}}global i32{{.*}}section ".ksyms"
+// CHECK: @CONFIG_HZ = external{{.*}}global i64{{.*}}section ".ksyms"
+// CHECK-NOT: @bpf_prog_active = internal
+// CHECK-NOT: @CONFIG_HZ = internal
+// Verify extern functions preserve linkage/calling convention/function signature
+// CHECK: declare ptr @bpf_kfunc_call_test_acquire(ptr){{.*}}section ".ksyms"
+// CHECK: declare void @bpf_kfunc_call_test_release(ptr){{.*}}section ".ksyms"
+// CHECK-NOT: declare internal{{.*}}@bpf_kfunc_call_test_acquire unnamed_addr #0
+// CHECK-NOT: declare internal{{.*}}@bpf_kfunc_call_test_release unnamed_addr #0
+// CHECK-NOT: declare{{.*}}fastcc{{.*}}@bpf_kfunc_call_test_acquire unnamed_addr #0 
+// CHECK-NOT: declare{{.*}}fastcc{{.*}}@bpf_kfunc_call_test_release unnamed_addr #0