<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/90358>90358</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Putting a function in a special `__TEXT,__foo` section results in underalignment
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          dougsonos
      </td>
    </tr>
</table>

<pre>
    To reproduce (on macOS):

```
// section_test.cpp
struct Class {
        __attribute__((section("__TEXT,__foo,regular,pure_instructions")))
        static int test(int x, int y)
        {
                return x + y;
        }
};

int main(int argc, const char*[])
{
        return Class::test(argc, argc);
}

// clang -c -o section_test.o section_test.cpp
// otool -l section_test.o
```

Output is:

```
Section
 sectname __foo
   segname __TEXT
      addr 0x0000000000000030
 size 0x0000000000000020
    offset 520
     align 2^1 (2)   <<<<<<<<<<< underaligned section
```

I would have hoped for an alignment of 4 because that is the (sub)target's `getMinFunctionAlignment()`.

Analysis so far:

- Section alignment comes from the most-aligned object in it - MCObjectStreamer
- the `llvm::Function` has an alignment of 2 (comments say: for C++ ABI reasons)
- the `MachineFunction` has an alignment of 4 (for arm64)
- normally the `MachineFunction`'s alignment is used, but because `hasSection()` is true for the Function, the alignment of 2 wins (logic in `AsmPrinter::getGVAlignment`)
- the `MCSection` remains aligned to 2 because all of its functions are aligned to 2
- the normal text section's alignment is 4 because the `MachineFunction`s are 4-byte-aligned and not overridden by AsmPrinter

This seems like a catch-22: the `MachineFunction` alignment should win, but is getting overridden by the section's alignment, yet the section's alignment comes from the llvm::Function, which doesn't know anything at all (would use 1 except for a C++ ABI reason making it 2).

Interestingly, a function that is not a C++ method declared inline in its class, if it has a section attribute, is aligned correctly.
</pre>
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