arm64:ilp32: add documentation on the ILP32 ABI for ARM64

Based on Andrew Pinski's original patch-series and adapted with changes
to reduce the duplication of code-paths and resolve issue found during
LTP testing.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Signed-off-by: Christoph Muellner <christoph.muellner@theobroma-systems.com>
Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>
Signed-off-by: Andrew Pinski <Andrew.Pinski@caviumnetworks.com>
Reviewed-by: David Daney <david.daney@cavium.com>

1 files changed, 55 insertions, 0 deletions

diff --git a/Documentation/arm64/ilp32.txt b/Documentation/arm64/ilp32.txt
new file mode 100644
index 000000000000..4f6860b7004a
--- /dev/null
+++ b/Documentation/arm64/ilp32.txt
@@ -0,0 +1,55 @@
+ILP32 AARCH64 SYSCALL ABI
+=========================
+Written by Andrew Pinski <apinski@cavium.com>
+Updated by Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
+
+
+This document describes the ILP32 syscall ABI and where it differs
+from the generic linux syscall interface.
+
+Some structures are changed to reduce the difference in the code path
+for both ILP32 and LP64 ABIs for signal handling.
+
+The following structures have been changed so the layout of the
+structures are the same between ILP32 and LP64 ABIs, including:
+ * sigval_t        contains pointers
+ * sigevent        Uses sigval_t which causes it to be the same.  Special
+                   handing is needed for reading; in the mq_notify syscall
+ * sigaction       Conversion is handled in the userland (glibc), as the
+		    userland data structures are defined in glibc anyway.
+
+A number of structures differ between ILP32 and LP64, including:
+ * timespec        uses time_t and suseconds_t
+ * timeval         uses time_t and suseconds_t
+ * stat            uses timespec/time_t
+ * semid64_ds      uses time_t.
+ * msqid64_ds      uses time_t.
+ * shmid64_ds      uses time_t.
+ * rt_sigframe     uses siginfo and ucontext.
+ * siginfo_t       uses clock_t and sigval_t
+ * ucontext        uses stack_t and sigset_t
+ * fd_set          This is done to avoid endian issues between ILP32 and
+		   LP64. Syscalls consuming fd_set use timespec.
+ * struct msgbuf   The specification of 'struct msgbuf' defines the 'mtype'
+                   field as a 'long' (i.e. 32bit for ILP32, but 64bit for
+		   LP64).  Functions that operate on 'struct msgbuf' need
+		   to be passed through the compat-syscalls to resolve
+		   this.
+ * stack_t         contains pointers (handled in the compatibility layer)
+
+Also the syscalls which normally would pass 64bit values as two arguments;
+now pass the 64bit value as one argument.  Also they have been renamed
+(removing the 64 from the name) to avoid confusion.
+The list of these LP64 syscalls reused by ILP32 clients is:
+ * fcntl
+ * statfs
+ * fstatfs
+ * truncate
+ * ftruncate
+ * lseek
+ * sendfile
+ * newfstatat
+ * fstat
+ * mmap
+ * fadvise64
+