Skip to content

Correct documentation for HFA return values #4527

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Apr 25, 2023
Merged

Correct documentation for HFA return values #4527

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
5 changes: 3 additions & 2 deletions docs/build/arm64-windows-abi-conventions.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -204,7 +204,7 @@ A type is considered to be an HFA or HVA if all of the following hold:
- It doesn't have any non-trivial default or copy constructors, destructors, or assignment operators,
- All of its members have the same HFA or HVA type, or are float, double, or neon types that match the other members' HFA or HVA types.

HFA and HVA values with four or fewer elements are returned in s0-s3, d0-d3, or v0-v3, as appropriate.
HVA values with four or fewer elements are returned in s0-s3, d0-d3, or v0-v3, as appropriate.

Types returned by value are handled differently depending on whether they have certain properties, and whether the function is a non-static member function. Types which have all of these properties,
Copy link

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Maybe clearer to explicitly state "non-HVA types" here?

Copy link

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Actually, nevermind; there are rules for both HVAs and HFAs that aren't stated here, so that fix doesn't really help. I'm trying to work out the exact rules...


Expand All @@ -214,9 +214,10 @@ Types returned by value are handled differently depending on whether they have c

and are returned by non-member functions or static member functions, use the following return style:

- Types that are HFAs with four or fewer elements are returned in s0-s3, d0-d3, or v0-v3, as appropriate.
- Types less than or equal to 8 bytes are returned in x0.
- Types less than or equal to 16 bytes are returned in x0 and x1, with x0 containing the lower-order 8 bytes.
- For types greater than 16 bytes, the caller shall reserve a block of memory of sufficient size and alignment to hold the result. The address of the memory block shall be passed as an additional argument to the function in x8. The callee may modify the result memory block at any point during the execution of the subroutine. The callee isn't required to preserve the value stored in x8.
- For other aggregate types, the caller shall reserve a block of memory of sufficient size and alignment to hold the result. The address of the memory block shall be passed as an additional argument to the function in x8. The callee may modify the result memory block at any point during the execution of the subroutine. The callee isn't required to preserve the value stored in x8.

All other types use this convention:

Expand Down