From: Yury Norov <ynorov@caviumnetworks.com>
To: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
        Catalin Marinas <catalin.marinas@arm.com>
Cc: Yury Norov <ynorov@caviumnetworks.com>,
        Andrew Pinski <pinskia@gmail.com>,
        Andrew Pinski <Andrew.Pinski@caviumnetworks.com>,
        Adam Borowski <kilobyte@angband.pl>,
        Chris Metcalf <cmetcalf@ezchip.com>,
        Steve Ellcey <sellcey@caviumnetworks.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@linaro.org>,
        Ramana Radhakrishnan <ramana.gcc@googlemail.com>,
        Florian Weimer <fweimer@redhat.com>,
        Bamvor Zhangjian <bamvor.zhangjian@huawei.com>,
        Andreas Schwab <schwab@suse.de>, Chris Metcalf <cmetcalf@mellanox.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>, schwidefsky@de.ibm.com,
        broonie@kernel.org, Joseph Myers <joseph@codesourcery.com>,
        christoph.muellner@theobroma-systems.com, szabolcs.nagy@arm.com,
        klimov.linux@gmail.com, Nathan_Lynch@mentor.com, agraf@suse.de,
        Prasun.Kapoor@caviumnetworks.com, geert@linux-m68k.org,
        philipp.tomsich@theobroma-systems.com, manuel.montezelo@gmail.com,
        linyongting@huawei.com, davem@davemloft.net, zhouchengming1@huawei.com
Subject: [PATCH 04/20] arm64: ilp32: add documentation on the ILP32 ABI for ARM64
Date: Thu,  2 Mar 2017 00:49:12 +0530
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Based on Andrew Pinski's patch-series.

Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>
---
 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 0000000..08935a3
--- /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.
+
+AARCH64/ILP32 userspace can pass garbage in the top halve of w0-w7 registers
+(syscall arguments). So top 32 bits are zeroed for them.
+
+Comparing to AARCH32, AARCH64/ILP32 has 64-bit length of following types:
+ino_t       is u64 type.
+off_t       is s64 type.
+blkcnt_t    is s64 type.
+fsblkcnt_t  is u64 type.
+fsfilcnt_t  is u64 type.
+rlim_t      is u64 type.
+
+AARCH64/ILP32 ABI uses standard syscall table which can be found at
+include/uapi/asm-generic/unistd.h, with the exceptions listed below.
+
+Syscalls which pass 64-bit values are handled by the code shared from
+AARCH32 and pass that value as a pair. Next syscalls are affected:
+fadvise64_64()
+fallocate()
+ftruncate64()
+pread64()
+pwrite64()
+readahead()
+sync_file_range()
+truncate64()
+
+ptrace() syscall is handled by compat version.
+
+shmat() syscall is handled by non-compat handler as aarch64/ilp32 has no
+limitation on 4-pages alignement for shared memory.
+
+statfs() and fstatfs() take the size of struct statfs as an argument.
+It is calculated differently in kernel and user spaces. So AARCH32 handlers
+are taken to handle it.
+
+struct rt_sigframe is redefined and contains struct compat_siginfo,
+as compat syscalls expects, and struct ilp32_sigframe, to handle
+AARCH64 register set and 32-bit userspace register representation.
+
+elf_gregset_t is taken from lp64 to handle registers properly.
-- 
2.7.4