Re: [PATCH] iommupt/amdv1: avoid GCOV builds triggering FIELD_PREP build failure

[Jason Gunthorpe]

On Tue, Mar 10, 2026 at 09:31:36AM -0700, Sherry Yang wrote:
> After enabling CONFIG_GCOV_KERNEL and CONFIG_GCOV_PROFILE_ALL, following
> build failure is observed:
> 
> In function 'amdv1pt_install_leaf_entry',
>     inlined from '__do_map_single_page' at drivers/iommu/generic_pt/fmt/../iommu_pt.h:650:3,
>     inlined from '__map_single_page0' at drivers/iommu/generic_pt/fmt/../iommu_pt.h:661:1,
>     inlined from 'pt_descend' at drivers/iommu/generic_pt/fmt/../pt_iter.h:391:9,
>     inlined from '__do_map_single_page' at drivers/iommu/generic_pt/fmt/../iommu_pt.h:657:10,
>     inlined from '__map_single_page1.constprop' at drivers/iommu/generic_pt/fmt/../iommu_pt.h:661:1:
> ././include/linux/compiler_types.h:706:45: error: call to '__compiletime_assert_71' declared with attribute error: FIELD_PREP: value too large for the field
>   706 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>       |
> 
> ......
> 
> drivers/iommu/generic_pt/fmt/amdv1.h:220:26: note: in expansion of macro 'FIELD_PREP'
>   220 |                          FIELD_PREP(AMDV1PT_FMT_OA,
>       |                          ^~~~~~~~~~
> 
> In the path '__do_map_single_page()', level 0 always invokes
> 'pt_install_leaf_entry(&pts, map->oa, PAGE_SHIFT, …)'. At runtime that
> lands in the 'if (oasz_lg2 == isz_lg2)' arm of 'amdv1pt_install_leaf_entry()';
> the contiguous-only 'else' block is unreachable for 4 KiB pages.

I think this is fixed already by

commit 98d5110f90ae0dbc5f2f13f033e06f6d57009e0d
Author: Jason Gunthorpe <jgg@xxxxxxxx>
Date:   Mon Jan 19 20:19:49 2026 -0400

    iommupt: Make it clearer to the compiler that pts.level == 0 for single page
    
    Older versions of gcc and clang sometimes get tripped up by the build time
    assertion in FIELD_PREP because they can see that the argument to
    FIELD_PREP is constant but can't see that the if condition protecting it
    is also a constant false.

       In file included from <command-line>:
       In function 'amdv1pt_install_leaf_entry',
           inlined from '__do_map_single_page' at drivers/iommu/generic_pt/fmt/../iommu_pt.h:651:3,
           inlined from '__map_single_page0' at drivers/iommu/generic_pt/fmt/../iommu_pt.h:662:1,
           inlined from 'pt_descend' at drivers/iommu/generic_pt/fmt/../pt_iter.h:391:9,
           inlined from '__do_map_single_page' at drivers/iommu/generic_pt/fmt/../iommu_pt.h:658:10,
           inlined from '__map_single_page1.constprop' at drivers/iommu/generic_pt/fmt/../iommu_pt.h:662:1:


??

Jason