[PATCH 02/18] arm64: ilp32: add documentation on the ILP32 ABI for ARM64

[Yury Norov]

Based on Andrew Pinski's patch-series.

Signed-off-by: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx>
---
 Documentation/arm64/ilp32.txt | 46 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 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..b96c18f
--- /dev/null
+++ b/Documentation/arm64/ilp32.txt
@@ -0,0 +1,46 @@
+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 potentially access top halves of registers that
+are passed as syscall arguments, so such registers (w0-w7) are deloused.
+
+AARCH64/ILP32 provides next types turned to 64-bit (comparing to AARCH32):
+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 64bit 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()
+sys_mmap()
+
+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 sfruct 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