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

[Evgeny Karpov]

On Wed, Apr 08, 2026, Jan Beulich wrote:
> On 08.04.2026 11:05, Evgeny Karpov wrote:
> > On Wed, Apr 08, 2026, Jan Beulich wrote:
> >> On 07.04.2026 19:12, Evgeny Karpov wrote:
> >>> 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.
> >>
> >> Applying 8-byte alignment uniformly might add padding between .idata$4 and
> >> .idata$5 for PE32, which likely is unwanted (and possibly is wrong).
> > 
> > Most likely, it does not break the PE format as it has an RVA to IAT, however it is 
> > definitely might bring unwanted padding to PE32.
> > 
> >>>>> 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.".
> >>
> >> If you insist on enforcing the alignment only for Arm64, then the code
> >> comment itself also wants extending to clarify why that target is special.
> >> As said, I think we should follow what MS tools do and arrange for 4- / 8-
> >> byte alignment for all targets.
> > 
> > Based on this suggestion, the patch can be changed to:
> > 
> > +      /* Align IAT (Import Address Table) to 8 bytes for PE32+.
> > +        https://learn.microsoft.com/en-us/windows/win32/debug/pe-format#import-address-table.  */
> > +      if (create_for_pep)
> > +       fprintf (f, "\t.align 3\n");
> 
> Any reason to then not also go the final small step and use
> 
>        fprintf (f, "\t.p2align %d\n", create_for_pep ? 3 : 2);

It looks like the alignment to 4 is not necessary because it is already aligned to
4 by INIT_SEC_DATA (IDATA5, ".idata$5", SEC_HAS_CONTENTS, 2).
 
> ? (Note that you can't use .align when no longer targeting a specific arch;
> it needs to be .balign or .p2align.)

It will be changed to .p2align.

Regards,
Evgeny