linux-kernel - [PATCH 07/24] arm64: ilp32: add documentation on the ILP32 ABI for ARM64

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Message-Id: <20180516081910.10067-8-ynorov@caviumnetworks.com>
Date:   Wed, 16 May 2018 11:18:52 +0300
From:   Yury Norov <ynorov@...iumnetworks.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Arnd Bergmann <arnd@...db.de>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-api@...r.kernel.org
Cc:     Yury Norov <ynorov@...iumnetworks.com>,
        Adam Borowski <kilobyte@...band.pl>,
        Alexander Graf <agraf@...e.de>,
        Alexey Klimov <klimov.linux@...il.com>,
        Andreas Schwab <schwab@...e.de>,
        Andrew Pinski <pinskia@...il.com>,
        Bamvor Zhangjian <bamv2005@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Christoph Muellner <christoph.muellner@...obroma-systems.com>,
        Dave Martin <Dave.Martin@....com>,
        "David S . Miller" <davem@...emloft.net>,
        Florian Weimer <fweimer@...hat.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        James Hogan <james.hogan@...tec.com>,
        James Morse <james.morse@....com>,
        Joseph Myers <joseph@...esourcery.com>,
        Lin Yongting <linyongting@...wei.com>,
        Manuel Montezelo <manuel.montezelo@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Nathan_Lynch <Nathan_Lynch@...tor.com>,
        Philipp Tomsich <philipp.tomsich@...obroma-systems.com>,
        Prasun Kapoor <Prasun.Kapoor@...iumnetworks.com>,
        Ramana Radhakrishnan <ramana.gcc@...glemail.com>,
        Steve Ellcey <sellcey@...iumnetworks.com>,
        Szabolcs Nagy <szabolcs.nagy@....com>
Subject: [PATCH 07/24] arm64: ilp32: add documentation on the ILP32 ABI for ARM64

Based on Andrew Pinski's patch-series.

Signed-off-by: Yury Norov <ynorov@...iumnetworks.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 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.
+
+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. Following 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 alignment 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 expect, and struct ilp32_ucontext, to handle
+AARCH64 register set and 32-bit userspace register representation.
+
+elf_gregset_t is taken from lp64 to handle registers properly.
-- 
2.17.0