Architectures that split 64-bit values across registers pairs usually do
so according to their C ABI calling convention (which means endianness).
Add some notes to that effect, and change the readahead example to show
a little endian example (since that is way more common than big endian).
Also start a new list of syscalls that this issue does not apply to.
Signed-off-by: Mike Frysinger <vapier@xxxxxxxxxx>
---
man2/syscall.2 | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/man2/syscall.2 b/man2/syscall.2
index fcb0a7e21248..80f83fd1aaac 100644
--- a/man2/syscall.2
+++ b/man2/syscall.2
@@ -102,13 +102,14 @@ Thus, using
instead of the wrapper provided by glibc,
the
.BR readahead ()
-system call would be invoked as follows on the ARM architecture with the EABI:
+system call would be invoked as follows on the ARM architecture with the EABI
+in little endian mode:
.in +4n
.nf
syscall(SYS_readahead, fd, 0,
- (unsigned int) (offset >> 32),
(unsigned int) (offset & 0xFFFFFFFF),
+ (unsigned int) (offset >> 32),
count);
.fi
.in
@@ -124,6 +125,8 @@ register pair.
That means inserting a dummy value into
.I r1
(the second argument of 0).
+Care also must be taken so that the split follows endian conventions
+(according to the C ABI for the platform).
Similar issues can occur on MIPS with the O32 ABI,
on PowerPC with the 32-bit ABI, and on Xtensa.
@@ -140,6 +143,11 @@ The affected system calls are
.BR sync_file_range (2),
and
.BR truncate64 (2).
+
+This does not affect syscalls that manually split and assemble 64-bit values
+such as
+.BR _llseek (2).
+Welcome to the wonderful world of historical baggage.
.SS Architecture calling conventions
Every architecture has its own way of invoking and passing arguments to the
kernel.
--
2.12.0
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