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Date: Fri, 3 May 2024 16:33:00 -0700
From: "Paul E. McKenney" <paulmck@kernel.org>
To: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Daniel Sneddon <daniel.sneddon@linux.intel.com>,
	Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Alexandre Chartre <alexandre.chartre@oracle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Sean Christopherson <seanjc@google.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Nikolay Borisov <nik.borisov@suse.com>,
	KP Singh <kpsingh@kernel.org>, Waiman Long <longman@redhat.com>,
	Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH v4 3/5] x86/syscall: Mark exit[_group] syscall handlers
 __noreturn
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On Fri, May 03, 2024 at 01:44:17PM -0700, Josh Poimboeuf wrote:
> On Fri, May 03, 2024 at 12:57:00PM -0700, Josh Poimboeuf wrote:
> > On Thu, May 02, 2024 at 04:48:13PM -0700, Paul McKenney wrote:
> > > On Sun, Apr 21, 2024 at 2:47 PM Paul McKenney <paulmckrcu@gmail.com> wrote:
> > > >
> > > > And this definitely helped, thank you!
> > > >
> > > > However, this one still remains:
> > > >
> > > > vmlinux.o: warning: objtool: ia32_sys_call+0x29b6:
> > > > __ia32_sys_exit_group() is missing a __noreturn annotation
> > > 
> > > And looking at the patched code, this function looks to me to be
> > > correctly marked.
> > > 
> > > No idea...  :-/
> > 
> > Ah, I think I missed fixing syscall_32.tbl.  Lemme see how to do that...
> 
> Can you try adding this on top?
> 
> diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
> index 5f8591ce7f25..f30b608d14dc 100644
> --- a/arch/x86/entry/syscalls/syscall_32.tbl
> +++ b/arch/x86/entry/syscalls/syscall_32.tbl
> @@ -12,7 +12,7 @@
>  # The abi is always "i386" for this file.
>  #
>  0	i386	restart_syscall		sys_restart_syscall
> -1	i386	exit			sys_exit
> +1	i386	exit			sys_exit			0 noreturn
>  2	i386	fork			sys_fork
>  3	i386	read			sys_read
>  4	i386	write			sys_write
> @@ -263,7 +263,7 @@
>  249	i386	io_cancel		sys_io_cancel
>  250	i386	fadvise64		sys_ia32_fadvise64
>  # 251 is available for reuse (was briefly sys_set_zone_reclaim)
> -252	i386	exit_group		sys_exit_group
> +252	i386	exit_group		sys_exit_group			0 noreturn
>  253	i386	lookup_dcookie
>  254	i386	epoll_create		sys_epoll_create
>  255	i386	epoll_ctl		sys_epoll_ctl

Thank you!

But for non-KCSAN builds, I get the following diagnostics:

In file included from arch/x86/entry/syscall_32.c:17:
/arch/x86/include/generated/asm/syscalls_32.h:2:20: error: expected declaration specifiers or ‘...’ before numeric constant
    2 | __SYSCALL_NORETURN(1, sys_exit)

For KCSAN builds, I instead get the following diagnostics:

In file included from arch/x86/entry/syscall_32.c:17:
/arch/x86/include/generated/asm/syscalls_32.h:2:20: error: expected parameter declarator
__SYSCALL_NORETURN(1, sys_exit)

Does arch/x86/entry/syscall_32.c need the following additional patch?

A quick smoke test passes, but perhaps I am just getting lucky...

							Thanx, Paul

------------------------------------------------------------------------

diff --git a/arch/x86/entry/syscall_32.c b/arch/x86/entry/syscall_32.c
index aab31760b4e3e..d9ae910ea6f33 100644
--- a/arch/x86/entry/syscall_32.c
+++ b/arch/x86/entry/syscall_32.c
@@ -14,9 +14,13 @@
 #endif
 
 #define __SYSCALL(nr, sym) extern long __ia32_##sym(const struct pt_regs *);
+#define __SYSCALL_NORETURN(nr, sym) extern long __noreturn __ia32_##sym(const struct pt_regs *);
 #include <asm/syscalls_32.h>
 #undef __SYSCALL
 
+#undef __SYSCALL_NORETURN
+#define __SYSCALL_NORETURN __SYSCALL
+
 #define __SYSCALL(nr, sym) __ia32_##sym,
 const sys_call_ptr_t ia32_sys_call_table[] = {
 #include <asm/syscalls_32.h>