Yury & Pavel,

On 24 May 2018, at 14:15, Yury Norov [off-list ref] wrote:

Hi Pavel,

On Wed, May 23, 2018 at 04:06:20PM +0200, Pavel Machek wrote:

quoted

On Wed 2018-05-16 11:18:52, Yury Norov wrote:

quoted

Based on Andrew Pinski's patch-series.

Signed-off-by: Yury Norov <redacted>

So Andrew's signoff should be here?

Yes it should, but it lost since v4. I'll restore it.

quoted

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---
Documentation/arm64/ilp32.txt | 45 +++++++++++++++++++++++++++++++++++
1 file changed, 45 insertions(+)
create mode 100644 Documentation/arm64/ilp32.txt

diff --git a/Documentation/arm64/ilp32.txt b/Documentation/arm64/ilp32.txt
new file mode 100644
index 000000000000..d0fd5109c4b2
--- /dev/null
+++ b/Documentation/arm64/ilp32.txt

@@ -0,0 +1,45 @@
+ILP32 AARCH64 SYSCALL ABI
+=========================
+
+This document describes the ILP32 syscall ABI and where it differs
+from the generic compat linux syscall interface.

I was hoping to learn what ILP32 is / what is it good for, but no,
this does not tell me... it would be good to do a short explanation
here, and maybe reference it from cover letter of the series...
								Pavel

ILP32 is ABI acronym that means "Integers, Longs and Pointers are 32-bit".
And LP64 means "Longs and Pointers are 64-bit”.

Just a nitpick: ILP32 is in fact just the memory model, but calling from ILP32
code into the Linux kernel requires modifications to the syscall-ABI due to
datastructure layout changing (every time a pointer or a ‘long’ is present in
a structure). As such structures are passed between the userspace and the
kernel (and also due to the fact that time_t is an ‘unsigned long’ in the C
language standard), modifications to the syscall ABI in Linux are needed to
support ILP32 processes calling into the kernel.

Things get a bit more involved, as the final consensus was to pass 64bit
quantities in the lower half of 2 64bit registers instead of as a single register:
this makes the way (on AArch64) that an ILP32 process calls into the kernel
more dissimilar from a LP64 process calling the same syscall.

What this rambling boils down to is: “ILP32" is the memory model, whereas
this series deals with the “Linux/AArch64 syscall ABI for ILP32 processes”.

Thanks,
Phil.

There's AN490 - "ILP32 for AArch64 Whitepaper" from ARM which covers
the topic:
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dai0490a/ar01s01.html

And some talks:
http://connect.linaro.org/resource/bkk16/bkk16-305b/

Briefly, ILP32 is 32-bit ABI that works with AARCH64 instruction set. It looks
better in some performance tests, and is useful for compatibility with 32-bit
legacy code.

If you're more familiar with x86 terminology, in ARM world LP64 corresponds
to x86_64, AARCH32_EL0 corresponds to x86_32, and ILP32 corresponds to x32
ABI.

I'll add link to AN490 in next submission.

Yury

quoted

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