Add support for -mcmodel=large relocations

Issue #27
davidlattimore · Aug 13, 2024 · 0eadaae · 0eadaae
1 parent c9cadf8
commit 0eadaae
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Showing 4 changed files with 53 additions and 9 deletions.
diff --git a/wild/tests/sources/cpp-integration.cc b/wild/tests/sources/cpp-integration.cc
@@ -13,6 +13,10 @@
 //#CompArgs:-fno-pie -fmerge-constants
 //#LinkArgs:--cc=g++ -no-pie -Wl,-z,now
 
+//#Config:model-large:default
+//#CompArgs:-mcmodel=large
+//#LinkArgs:--cc=g++ -Wl,-z,now
+
 #include <iostream>
 #include <string>
 

diff --git a/wild_lib/src/elf.rs b/wild_lib/src/elf.rs
@@ -382,10 +382,25 @@ const _ASSERTS: () = {
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub(crate) enum RelocationKind {
     Absolute,
+
+    /// The address of the symbol, relative to the place of the relocation.
     Relative,
-    Got,
+
+    /// The address of the symbol, relative to the base address of the GOT.
+    SymRelGotBase,
+
+    /// The offset of the symbol's GOT entry, relative to the start of the GOT.
+    GotRelGotBase,
+
+    /// The address of the symbol's PLT entry, relative to the base address of the GOT.
+    PltRelGotBase,
+
+    /// The address of the symbol's PLT entry, relative to the place of relocation.
     PltRelative,
+
+    /// The address of the symbol's GOT entry, relative to the place of the relocation.
     GotRelative,
+
     TlsGd,
     TlsLd,
     DtpOff,
@@ -408,9 +423,20 @@ impl RelocationKindInfo {
         let (kind, size) = match r_type {
             object::elf::R_X86_64_64 => (RelocationKind::Absolute, 8),
             object::elf::R_X86_64_PC32 => (RelocationKind::Relative, 4),
-            object::elf::R_X86_64_GOT32 => (RelocationKind::Got, 4),
+            object::elf::R_X86_64_PC64 => (RelocationKind::Relative, 8),
+            object::elf::R_X86_64_GOT32 => (RelocationKind::GotRelGotBase, 4),
+            object::elf::R_X86_64_GOT64 => (RelocationKind::GotRelGotBase, 8),
+            object::elf::R_X86_64_GOTOFF64 => (RelocationKind::SymRelGotBase, 8),
             object::elf::R_X86_64_PLT32 => (RelocationKind::PltRelative, 4),
+            object::elf::R_X86_64_PLTOFF64 => (RelocationKind::PltRelGotBase, 8),
             object::elf::R_X86_64_GOTPCREL => (RelocationKind::GotRelative, 4),
+
+            // For now, we rely on GOTPC64 and GOTPC32 always referencing the symbol
+            // _GLOBAL_OFFSET_TABLE_, which means that we can just treat these a normal relative
+            // relocations and avoid any special processing when writing.
+            object::elf::R_X86_64_GOTPC64 => (RelocationKind::Relative, 8),
+            object::elf::R_X86_64_GOTPC32 => (RelocationKind::Relative, 4),
+
             object::elf::R_X86_64_32 | object::elf::R_X86_64_32S => (RelocationKind::Absolute, 4),
             object::elf::R_X86_64_16 => (RelocationKind::Absolute, 2),
             object::elf::R_X86_64_PC16 => (RelocationKind::Relative, 2),

diff --git a/wild_lib/src/elf_writer.rs b/wild_lib/src/elf_writer.rs
@@ -1502,6 +1502,12 @@ fn apply_relocation(
             .got_address()?
             .wrapping_add(addend)
             .wrapping_sub(place),
+        RelocationKind::GotRelGotBase => resolution
+            .got_address()?
+            .sub(layout.got_base())
+            .wrapping_add(addend),
+        RelocationKind::SymRelGotBase => resolution.value().wrapping_sub(layout.got_base()),
+        RelocationKind::PltRelGotBase => resolution.plt_address()?.wrapping_sub(layout.got_base()),
         RelocationKind::PltRelative => resolution
             .plt_address()?
             .wrapping_add(addend)
@@ -1534,7 +1540,6 @@ fn apply_relocation(
             .wrapping_sub(layout.tls_end_address())
             .wrapping_add(addend),
         RelocationKind::None => 0,
-        other => bail!("Unsupported relocation kind {other:?}"),
     };
     let value_bytes = value.to_le_bytes();
     let end = offset_in_section as usize + rel_info.byte_size;

diff --git a/wild_lib/src/layout.rs b/wild_lib/src/layout.rs
@@ -1211,6 +1211,11 @@ impl<'data> Layout<'data> {
         let group_layout = &self.group_layouts[file_id.group()];
         &group_layout.files[file_id.file()]
     }
+
+    /// Returns the base address of the global offset table.
+    pub(crate) fn got_base(&self) -> u64 {
+        self.section_layouts.get(output_section_id::GOT).mem_offset
+    }
 }
 
 fn layout_sections(
@@ -2161,15 +2166,19 @@ fn process_relocation(
 
 fn resolution_flags(rel_kind: RelocationKind) -> ResolutionFlags {
     match rel_kind {
-        RelocationKind::PltRelative => ResolutionFlags::PLT | ResolutionFlags::GOT,
-        RelocationKind::Got | RelocationKind::GotRelative => ResolutionFlags::GOT,
+        RelocationKind::PltRelative | RelocationKind::PltRelGotBase => {
+            ResolutionFlags::PLT | ResolutionFlags::GOT
+        }
+        RelocationKind::GotRelGotBase | RelocationKind::GotRelative => ResolutionFlags::GOT,
         RelocationKind::GotTpOff => ResolutionFlags::GOT_TLS_OFFSET,
         RelocationKind::TlsGd => ResolutionFlags::GOT_TLS_MODULE,
         RelocationKind::TlsLd => ResolutionFlags::empty(),
-        RelocationKind::Absolute => ResolutionFlags::DIRECT,
-        RelocationKind::Relative => ResolutionFlags::DIRECT,
-        RelocationKind::DtpOff | RelocationKind::TpOff => ResolutionFlags::DIRECT,
-        RelocationKind::None => ResolutionFlags::DIRECT,
+        RelocationKind::Absolute
+        | RelocationKind::Relative
+        | RelocationKind::DtpOff
+        | RelocationKind::TpOff
+        | RelocationKind::SymRelGotBase
+        | RelocationKind::None => ResolutionFlags::DIRECT,
     }
 }