From d9817f63d5dded8efbfde4ea7f7c268e590b267c Mon Sep 17 00:00:00 2001
From: Luke Street <luke@street.dev>
Date: Wed, 4 Sep 2024 19:56:22 -0600
Subject: [PATCH] Fix .note.split warnings for older mwld versions

Prior to mwld GC 3.0a3, the linker doesn't support ELF .note sections
properly. With GC 2.7, it crashes if the section type is SHT_NOTE.
Use the same section type as .mwcats.* so the linker ignores it.
---
 src/util/elf.rs | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/util/elf.rs b/src/util/elf.rs
index 1ef2cd3..0281600 100644
--- a/src/util/elf.rs
+++ b/src/util/elf.rs
@@ -12,7 +12,7 @@ use indexmap::IndexMap;
 use objdiff_core::obj::split_meta::{SplitMeta, SHT_SPLITMETA, SPLITMETA_SECTION};
 use object::{
     elf,
-    elf::{SHF_ALLOC, SHF_EXECINSTR, SHF_WRITE, SHT_NOBITS, SHT_PROGBITS},
+    elf::{SHF_ALLOC, SHF_EXECINSTR, SHF_WRITE, SHT_LOUSER, SHT_NOBITS, SHT_PROGBITS},
     write::{
         elf::{ProgramHeader, Rel, SectionHeader, SectionIndex, SymbolIndex, Writer},
         StringId,
@@ -34,6 +34,8 @@ use crate::{
     },
 };
 
+pub const SHT_MWCATS: u32 = SHT_LOUSER + 0x4A2A82C2;
+
 enum BoundaryState {
     /// Looking for a file symbol, any section symbols are queued
     LookForFile(Vec<(u64, String)>),
@@ -456,7 +458,7 @@ pub fn write_elf(obj: &ObjInfo, export_all: bool) -> Result<Vec<u8>> {
     };
 
     // Generate .note.split section
-    let mut split_meta = if let Some(metadata) = &obj.split_meta {
+    let mut split_meta = if let (Some(metadata), Some(_)) = (&obj.split_meta, &obj.mw_comment) {
         // Reserve section
         let name = writer.add_section_name(SPLITMETA_SECTION.as_bytes());
         let index = writer.reserve_section_index();
@@ -825,9 +827,16 @@ pub fn write_elf(obj: &ObjInfo, export_all: bool) -> Result<Vec<u8>> {
     // Write .note.split section header
     if let Some((metadata, idx)) = &split_meta {
         let out_section = &out_sections[*idx];
+        let mut sh_type = SHT_SPLITMETA;
+        if matches!(&obj.mw_comment, Some(comment) if comment.version < 14) {
+            // Prior to mwld GC 3.0a3, the linker doesn't support ELF .note sections
+            // properly. With GC 2.7, it crashes if the section type is SHT_NOTE.
+            // Use the same section type as .mwcats.* so the linker ignores it.
+            sh_type = SHT_MWCATS;
+        }
         writer.write_section_header(&SectionHeader {
             name: Some(out_section.name),
-            sh_type: SHT_SPLITMETA,
+            sh_type,
             sh_flags: 0,
             sh_addr: 0,
             sh_offset: out_section.offset as u64,