Merge pull request #125 from kubkon/elf-aarch64-thunks

elf: thunks algorithm fixes
kubkon · Mar 11, 2024 · 60afc8a · 60afc8a
2 parents 19cd7ed + 1bb8134
commit 60afc8a
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Showing 3 changed files with 75 additions and 3 deletions.
diff --git a/src/Elf.zig b/src/Elf.zig
@@ -2236,6 +2236,8 @@ fn writeAtoms(self: *Elf) !void {
     const tracy = trace(@src());
     defer tracy.end();
 
+    const gpa = self.base.allocator;
+
     const slice = self.sections.slice();
     for (slice.items(.shdr), slice.items(.atoms)) |shdr, atoms| {
         if (atoms.items.len == 0) continue;
@@ -2274,6 +2276,16 @@ fn writeAtoms(self: *Elf) !void {
         try self.base.file.pwriteAll(buffer, shdr.sh_offset);
     }
 
+    for (self.thunks.items) |thunk| {
+        const shdr = slice.items(.shdr)[thunk.out_shndx];
+        const offset = thunk.value + shdr.sh_offset;
+        const buffer = try gpa.alloc(u8, thunk.size(self));
+        defer gpa.free(buffer);
+        var stream = std.io.fixedBufferStream(buffer);
+        try thunk.write(self, stream.writer());
+        try self.base.file.pwriteAll(buffer, offset);
+    }
+
     try self.reportUndefs();
 }
 

diff --git a/src/Elf/thunks.zig b/src/Elf/thunks.zig
@@ -18,12 +18,12 @@ pub fn createThunks(shndx: u32, elf_file: *Elf) !void {
         start_atom.value = try advance(shdr, start_atom.size, start_atom.alignment);
         i += 1;
 
-        while (i < atoms.len and
-            shdr.sh_size - start_atom.value < maxAllowedDistance(cpu_arch)) : (i += 1)
-        {
+        while (i < atoms.len) : (i += 1) {
             const atom_index = atoms[i];
             const atom = elf_file.getAtom(atom_index).?;
             assert(atom.flags.alive);
+            const alignment = try math.powi(u32, 2, atom.alignment);
+            if (mem.alignForward(u64, shdr.sh_size, alignment) - start_atom.value >= maxAllowedDistance(cpu_arch)) break;
             atom.value = try advance(shdr, atom.size, atom.alignment);
         }
 

diff --git a/test/elf.zig b/test/elf.zig
@@ -62,6 +62,7 @@ pub fn addElfTests(b: *Build, options: common.Options) *Step {
     elf_step.dependOn(testSharedAbsSymbol(b, opts));
     elf_step.dependOn(testStrip(b, opts));
     elf_step.dependOn(testThunks(b, opts));
+    elf_step.dependOn(testThunks2(b, opts));
     elf_step.dependOn(testTlsCommon(b, opts));
     elf_step.dependOn(testTlsDesc(b, opts));
     elf_step.dependOn(testTlsDescImport(b, opts));
@@ -2165,6 +2166,65 @@ fn testThunks(b: *Build, opts: Options) *Step {
     return test_step;
 }
 
+fn testThunks2(b: *Build, opts: Options) *Step {
+    const test_step = b.step("test-elf-thunks2", "");
+
+    if (builtin.target.cpu.arch != .aarch64) return skipTestStep(test_step);
+
+    const src =
+        \\#include <stdio.h>
+        \\__attribute__((aligned(0x8000000))) int bar() {
+        \\  return 42;
+        \\}
+        \\int foobar();
+        \\int foo() {
+        \\  return bar() - foobar();
+        \\}
+        \\__attribute__((aligned(0x8000000))) int foobar() {
+        \\  return 42;
+        \\}
+        \\int main() {
+        \\  printf("bar=%d, foo=%d, foobar=%d", bar(), foo(), foobar());
+        \\  return foo();
+        \\}
+    ;
+
+    {
+        const exe = cc(b, "a.out", opts);
+        exe.addCSource(src);
+        exe.addArg("-ffunction-sections");
+
+        const run = exe.run();
+        run.expectStdOutEqual("bar=42, foo=0, foobar=42");
+        run.expectExitCode(0);
+        test_step.dependOn(run.step());
+
+        const check = exe.check();
+        check.max_bytes = std.math.maxInt(u32);
+        check.checkInSymtab();
+        check.checkContains("_libc_start_main$thunk");
+        test_step.dependOn(&check.step);
+    }
+
+    {
+        const exe = cc(b, "a.out", opts);
+        exe.addCSource(src);
+
+        const run = exe.run();
+        run.expectStdOutEqual("bar=42, foo=0, foobar=42");
+        run.expectExitCode(0);
+        test_step.dependOn(run.step());
+
+        const check = exe.check();
+        check.max_bytes = std.math.maxInt(u32);
+        check.checkInSymtab();
+        check.checkContains("_libc_start_main$thunk");
+        test_step.dependOn(&check.step);
+    }
+
+    return test_step;
+}
+
 fn testTlsCommon(b: *Build, opts: Options) *Step {
     const test_step = b.step("test-elf-tls-common", "");