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Date:   Sun, 27 Feb 2022 10:45:13 -0800
From:   Kees Cook <>
To:     Kees Cook <>
Cc:     David Gow <>,
        "Gustavo A. R. Silva" <>,
        Nathan Chancellor <>,
        Nick Desaulniers <>,
        Rasmus Villemoes <>,
        Vitor Massaru Iha <>,
        Daniel Latypov <>,
        Anton Ivanov <>,
        Jeff Dike <>,
        Richard Weinberger <>,
        Masahiro Yamada <>,
        Arnd Bergmann <>,,,,,,,
Subject: [PATCH v3 3/7] um: Cleanup syscall_handler_t definition/cast, fix warning

From: David Gow <>

The syscall_handler_t type for x86_64 was defined as 'long (*)(void)',
but always cast to 'long (*)(long, long, long, long, long, long)' before
use. This now triggers a warning (see below).

Define syscall_handler_t as the latter instead, and remove the cast.
This simplifies the code, and fixes the warning.

In file included from ../arch/um/include/asm/processor-generic.h:13
                 from ../arch/x86/um/asm/processor.h:41
                 from ../include/linux/rcupdate.h:30
                 from ../include/linux/rculist.h:11
                 from ../include/linux/pid.h:5
                 from ../include/linux/sched.h:14
                 from ../include/linux/ptrace.h:6
                 from ../arch/um/kernel/skas/syscall.c:7:
../arch/um/kernel/skas/syscall.c: In function ‘handle_syscall’:
../arch/x86/um/shared/sysdep/syscalls_64.h:18:11: warning: cast between incompatible function types from ‘long int (*)(void)’ to ‘long int (*)(long int,  long int,  long int,  long int,  long int,  long int)’ [
   18 |         (((long (*)(long, long, long, long, long, long)) \
      |           ^
../arch/x86/um/asm/ptrace.h:36:62: note: in definition of macro ‘PT_REGS_SET_SYSCALL_RETURN’
   36 | #define PT_REGS_SET_SYSCALL_RETURN(r, res) (PT_REGS_AX(r) = (res))
      |                                                              ^~~
../arch/um/kernel/skas/syscall.c:46:33: note: in expansion of macro ‘EXECUTE_SYSCALL’
   46 |                                 EXECUTE_SYSCALL(syscall, regs));
      |                                 ^~~~~~~~~~~~~~~

Signed-off-by: David Gow <>
Signed-off-by: Kees Cook <>
This is just a re-send of the above linked patch, collecting it into this series.
 arch/x86/um/shared/sysdep/syscalls_64.h | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/um/shared/sysdep/syscalls_64.h b/arch/x86/um/shared/sysdep/syscalls_64.h
index 48d6cd12f8a5..b6b997225841 100644
--- a/arch/x86/um/shared/sysdep/syscalls_64.h
+++ b/arch/x86/um/shared/sysdep/syscalls_64.h
@@ -10,13 +10,12 @@
 #include <linux/msg.h>
 #include <linux/shm.h>
-typedef long syscall_handler_t(void);
+typedef long syscall_handler_t(long, long, long, long, long, long);
 extern syscall_handler_t *sys_call_table[];
 #define EXECUTE_SYSCALL(syscall, regs) \
-	(((long (*)(long, long, long, long, long, long)) \
-	  (*sys_call_table[syscall]))(UPT_SYSCALL_ARG1(&regs->regs), \
+	(((*sys_call_table[syscall]))(UPT_SYSCALL_ARG1(&regs->regs), \
 		 		      UPT_SYSCALL_ARG2(&regs->regs), \
 				      UPT_SYSCALL_ARG3(&regs->regs), \
 				      UPT_SYSCALL_ARG4(&regs->regs), \

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