[PATCH] Fix IAT (Import Address Table) alignment on AArch64

[Evgeny Karpov]

On Tue, Apr 07, 2026, Jan Beulich wrote:
> On 07.04.2026 16:47, Evgeny Karpov wrote:
> > On Tue, Apr 07, 2026, Jan Beulich wrote:
> >> On 07.04.2026 11:48, Evgeny Karpov wrote:
> >>> The IAT should be aligned to 8 bytes in aarch64-w64-mingw32, otherwise, it might
> >>> result in relocation issues.
> >>
> >> What is it that makes this different on aarch64? IOW I wonder if this is
> >> going too far or not far enough.
> >>
> >>> binutils/ChangeLog:
> >>>
> >>> 	* dlltool.c (make_head): Update.
> >>
> >> Please either omit the ChangeLog entry, or have it say something meaningful.
> > 
> > The updated decription:
> > ---
> > The IAT should be aligned to 8 bytes in aarch64-w64-mingw32, otherwise, it might
> > result in relocation issues.
> > 
> > When a function is imported from DLL, it generates the following code:
> > 
> > adrp    x19, __imp_fn
> > ldr     x19, [x19, #:lo12:__imp_fn]
> > 
> > 8 byte alignment is required for ldr relocation. Addresses are placed in IAT.
> > The size of the chunk on AArch64 is 8 bytes.
> > If IAT is not aligned to 8 bytes, the relocation issue appears.
> > This patch fixes this issue.
> 
> Much better, thanks. This addresses part of my earlier remark then as well,
> clarifying it's not "too much" that you do. The "too little" aspect remains,
> though: Looking at a random ia64 archive, I see .idata$5 to have 8-byte
> alignment there as well. Shouldn't .idata$5 always have machine-word
> alignment?

Based on PE Format documentation
https://learn.microsoft.com/en-us/windows/win32/debug/pe-format#import-address-table

4 byte addresses are used for PE32 and 8 byte addresses are used for PE32+.
There is no definition about the alignment, however it might be optional.
8 byte alignment appears as a requirement for an architecture.
For example, it requires 8 byte alignment for ldr relocation on AArch64.

Potentially, 8 byte alignment might be applied to all architectures,
however this might not be necessary for other relocations and could
slightly unnecessarily increase the size.

> > binutils/ChangeLog:
> > 
> >         * dlltool.c (make_head): Add 8 byte alignment.
> 
> This sadly still gives the impression of wider a change (all targets) than
> there is.

It will be changed to "Add 8 byte alignment on AArch64.".

Regards,
Evgeny