elf: handle .ifunc action for dynamic abs relocs

kubkon · Jul 11, 2023 · d3caa57 · d3caa57
1 parent d461c91
commit d3caa57
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Showing 3 changed files with 36 additions and 26 deletions.
diff --git a/src/Elf.zig b/src/Elf.zig
@@ -87,6 +87,7 @@ comdat_groups_owners: std.ArrayListUnmanaged(ComdatGroupOwner) = .{},
 comdat_groups_table: std.AutoHashMapUnmanaged(u32, ComdatGroupOwner.Index) = .{},
 
 needs_tlsld: bool = false,
+num_ifunc_dynrelocs: usize = 0,
 default_sym_version: elf.Elf64_Versym,
 
 pub fn openPath(allocator: Allocator, options: Options, thread_pool: *ThreadPool) !*Elf {
@@ -2444,7 +2445,7 @@ fn sortRelaDyn(self: *Elf) void {
 }
 
 fn getNumIRelativeRelocs(self: *Elf) usize {
-    var count: usize = 0;
+    var count: usize = self.num_ifunc_dynrelocs;
 
     for (self.got.symbols.items) |sym_index| {
         const sym = self.getSymbol(sym_index);

diff --git a/src/Elf/Atom.zig b/src/Elf/Atom.zig
@@ -315,17 +315,12 @@ fn scanReloc(self: Atom, symbol: *Symbol, rel: elf.Elf64_Rela, action: RelocActi
             }
         },
 
-        .dynrel => {
+        .dynrel, .baserel, .ifunc => {
             self.checkTextReloc(symbol, elf_file);
             object.num_dynrelocs += 1;
-        },
 
-        .baserel => {
-            self.checkTextReloc(symbol, elf_file);
-            object.num_dynrelocs += 1;
+            if (action == .ifunc) elf_file.num_ifunc_dynrelocs += 1;
         },
-
-        .ifunc => self.unhandledRelocError(symbol, rel, action, elf_file),
     }
 }
 
@@ -348,23 +343,6 @@ inline fn checkTextReloc(self: Atom, symbol: *const Symbol, elf_file: *Elf) void
     }
 }
 
-inline fn unhandledRelocError(
-    self: Atom,
-    symbol: *const Symbol,
-    rel: elf.Elf64_Rela,
-    action: RelocAction,
-    elf_file: *Elf,
-) void {
-    elf_file.base.fatal("{s}: {s}: unhandled {} relocation at offset 0x{x} against symbol '{s}': action {s}", .{
-        self.getObject(elf_file).fmtPath(),
-        self.getName(elf_file),
-        fmtRelocType(rel.r_type()),
-        rel.r_offset,
-        symbol.getName(elf_file),
-        @tagName(action),
-    });
-}
-
 inline fn noPicError(self: Atom, symbol: *const Symbol, rel: elf.Elf64_Rela, elf_file: *Elf) void {
     elf_file.base.fatal(
         "{s}: {s}: {} relocation at offset 0x{x} against symbol '{s}' cannot be used; recompile with -fno-PIC",
@@ -726,7 +704,14 @@ fn resolveDynAbsReloc(
             });
         },
 
-        .ifunc => self.unhandledRelocError(target, rel, action, elf_file),
+        .ifunc => {
+            const S_ = @as(i64, @intCast(target.getAddress(.{ .plt = false }, elf_file)));
+            elf_file.addRelaDynAssumeCapacity(.{
+                .offset = P,
+                .type = elf.R_X86_64_IRELATIVE,
+                .addend = S_ + A,
+            });
+        },
     }
 }
 

diff --git a/test/elf.zig b/test/elf.zig
@@ -7,6 +7,7 @@ pub fn addElfTests(b: *Build, opts: Options) *Step {
         elf_step.dependOn(testCopyrelAlias(b, opts));
         elf_step.dependOn(testDsoIfunc(b, opts));
         elf_step.dependOn(testDsoPlt(b, opts));
+        elf_step.dependOn(testIfuncAlias(b, opts));
         elf_step.dependOn(testIfuncDynamic(b, opts));
         elf_step.dependOn(testIfuncFuncPtr(b, opts));
         elf_step.dependOn(testIfuncNoPlt(b, opts));
@@ -195,6 +196,28 @@ fn testDsoPlt(b: *Build, opts: Options) *Step {
     return test_step;
 }
 
+fn testIfuncAlias(b: *Build, opts: Options) *Step {
+    const test_step = b.step("test-elf-ifunc-alias", "");
+
+    const exe = cc(b, null, opts);
+    exe.addSourceBytes(
+        \\#include <assert.h>
+        \\void foo() {}
+        \\int bar() __attribute__((ifunc("resolve_bar")));
+        \\void *resolve_bar() { return foo; }
+        \\void *bar2 = bar;
+        \\int main() {
+        \\  assert(bar == bar2);
+        \\}
+    , "main.c");
+    exe.addArg("-fPIC");
+
+    const run = exe.run();
+    test_step.dependOn(run.step());
+
+    return test_step;
+}
+
 fn testIfuncDynamic(b: *Build, opts: Options) *Step {
     const test_step = b.step("test-elf-ifunc-dynamic", "");
 
@@ -309,6 +332,7 @@ fn testIfuncStatic(b: *Build, opts: Options) *Step {
 
     const exe = cc(b, null, opts);
     exe.addSourceBytes(
+        \\#include <stdio.h>
         \\void foo() __attribute__((ifunc("resolve_foo")));
         \\void hello() {
         \\  printf("Hello world\n");