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From 2d85a5b7a1011386d66cc36512a54e80b6cfa515 Mon Sep 17 00:00:00 2001
From: Cheyenne Wills <cwills@sinenomine.net>
Date: Fri, 22 Jan 2021 07:57:55 -0700
Subject: [PATCH 8/8] Linux 5.11: Test 32bit compat with in_compat_syscall
Linux 5.11 removed the TIF_IA32 thread flag with commit:
x86: Reclaim TIF_IA32 and TIF_X32 (8d71d2bf6efec)
The flag TIF_IA32 was being used by openafs to determine if the task was
handling a syscall request from a 32 bit process. Building against a
Linux 5.11 kernel results in a build failure as TIF_IA32 is undefined.
The function 'in_compat_syscall' was introduced in Linux 4.6 as
the preferred method to determine if a syscall needed to handle a
compatible call (e.g. 32bit application).
To resolve the build problem, use 'in_compat_syscall' if present (Linux
4.6 and later) to determine if the syscall needs to handle a
compatibility mode call.
Add autoconf check for in_compat_syscall.
Notes about in_compat_syscall:
In Linux 4.6 'in_compat_syscall' was defined for all architectures with
a generic return of 'is_compat_task', but allows architecture specific
overriding implementations (x86 and sparc).
At 4.6 (and later), the function 'is_compat_task' is defined only for
the following architectures to return:
Arch Returns
======= ==============================
arm64 test_thread_flag(TIF_32BIT);
mips test_thread_flag(TIF_32BIT_ADDR)
parisc test_ti_thread_flag(task_thread_info(t), TIF_32BIT)
powerpc is_32bit_task()
s390 test_thread_flag(TIF_31BIT)
sparc test_thread_flag(TIF_32BIT)
If the Linux kernel is not built with compat mode, is_compat_task and
in_compat_syscall is set to always return 0
Linux commit that introduced in_compat_syscall:
compat: add in_compat_syscall to ask whether we're in a compat syscall
(5180e3e24fd3e8e7)
Reviewed-on: https://gerrit.openafs.org/14499
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit 78ef922612bef5f5fd6904896e84b9d2ea802404)
Change-Id: I4eca62f19ae58fd830915feff5098cec2825f099
Reviewed-on: https://gerrit.openafs.org/14511
Reviewed-by: Cheyenne Wills <cwills@sinenomine.net>
Tested-by: Cheyenne Wills <cwills@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>
---
src/afs/LINUX/osi_machdep.h | 4 +++-
src/cf/linux-kernel-func.m4 | 6 ++++++
2 files changed, 9 insertions(+), 1 deletion(-)
diff --git a/src/afs/LINUX/osi_machdep.h b/src/afs/LINUX/osi_machdep.h
index 9ecdaf0bf..066c1885f 100644
--- a/src/afs/LINUX/osi_machdep.h
+++ b/src/afs/LINUX/osi_machdep.h
@@ -167,7 +167,9 @@ static inline long copyinstr(char *from, char *to, int count, int *length) {
static inline int
afs_in_compat_syscall(void)
{
-# if defined(AFS_SPARC64_LINUX26_ENV)
+# if defined(HAVE_LINUX_IN_COMPAT_SYSCALL)
+ return in_compat_syscall();
+# elif defined(AFS_SPARC64_LINUX26_ENV)
return test_thread_flag(TIF_32BIT);
# elif defined(AFS_SPARC64_LINUX24_ENV)
return (current->thread.flags & SPARC_FLAG_32BIT) != 0;
diff --git a/src/cf/linux-kernel-func.m4 b/src/cf/linux-kernel-func.m4
index e45a30540..5b4060238 100644
--- a/src/cf/linux-kernel-func.m4
+++ b/src/cf/linux-kernel-func.m4
@@ -157,6 +157,12 @@ AC_CHECK_LINUX_FUNC([lru_cache_add_file],
[#include <linux/swap.h>],
[lru_cache_add_file(NULL);])
+dnl Linux 4.6 introduced in_compat_syscall as replacement for is_compat_task
+dnl for certain platforms.
+AC_CHECK_LINUX_FUNC([in_compat_syscall],
+ [#include <linux/compat.h>],
+ [in_compat_syscall();])
+
dnl lru_cache_add exported in Linux 5.8
dnl replaces lru_cache_add_file
AC_CHECK_LINUX_FUNC([lru_cache_add],
--
2.30.1
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