Re: [PATCH v4 3/5] x86/syscall: Mark exit[_group] syscall handlers __noreturn

[Paul E. McKenney]

On Fri, Apr 19, 2024 at 02:09:49PM -0700, Josh Poimboeuf wrote:
> The direct-call syscall dispatch functions don't know that the exit()
> and exit_group() syscall handlers don't return.  As a result the call
> sites aren't optimized accordingly.
> 
> Fix that by marking those exit syscall declarations as __noreturn.
> 
> Fixes the following warnings:
> 
>   vmlinux.o: warning: objtool: x64_sys_call+0x2804: __x64_sys_exit() is missing a __noreturn annotation
>   vmlinux.o: warning: objtool: ia32_sys_call+0x29b6: __ia32_sys_exit_group() is missing a __noreturn annotation
> 
> Fixes: 7390db8aea0d ("x86/bhi: Add support for clearing branch history at syscall entry")
> Reported-by: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
> Closes: https://lkml.kernel.org/lkml/6dba9b32-db2c-4e6d-9500-7a08852f17a3@paulmck-laptop
> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

Looks good, but it does not apply on top of current -next and I don't
trust myself to hand-apply it (something about having just got off of
a flight across the big pond).

Could you please let me know what else do I need to pull in to be able
to cleanly apply this one?

							Thanx, Paul

> ---
>  arch/x86/entry/syscall_64.c            | 4 ++++
>  arch/x86/entry/syscall_x32.c           | 4 ++++
>  arch/x86/entry/syscalls/syscall_64.tbl | 6 +++---
>  arch/x86/um/sys_call_table_32.c        | 1 +
>  arch/x86/um/sys_call_table_64.c        | 1 +
>  scripts/syscalltbl.sh                  | 6 ++++--
>  tools/objtool/noreturns.h              | 4 ++++
>  7 files changed, 21 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/entry/syscall_64.c b/arch/x86/entry/syscall_64.c
> index 96ea1f8a1d3f..ff36a993a07e 100644
> --- a/arch/x86/entry/syscall_64.c
> +++ b/arch/x86/entry/syscall_64.c
> @@ -8,9 +8,13 @@
>  #include <asm/syscall.h>
>  
>  #define __SYSCALL(nr, sym) extern long __x64_##sym(const struct pt_regs *);
> +#define __SYSCALL_NORETURN(nr, sym) extern long __noreturn __x64_##sym(const struct pt_regs *);
>  #include <asm/syscalls_64.h>
>  #undef __SYSCALL
>  
> +#undef __SYSCALL_NORETURN
> +#define __SYSCALL_NORETURN __SYSCALL
> +
>  #define __SYSCALL(nr, sym) __x64_##sym,
>  const sys_call_ptr_t sys_call_table[] = {
>  #include <asm/syscalls_64.h>
> diff --git a/arch/x86/entry/syscall_x32.c b/arch/x86/entry/syscall_x32.c
> index 5aef4230faca..4221ecce6e68 100644
> --- a/arch/x86/entry/syscall_x32.c
> +++ b/arch/x86/entry/syscall_x32.c
> @@ -8,9 +8,13 @@
>  #include <asm/syscall.h>
>  
>  #define __SYSCALL(nr, sym) extern long __x64_##sym(const struct pt_regs *);
> +#define __SYSCALL_NORETURN(nr, sym) extern long __noreturn __x64_##sym(const struct pt_regs *);
>  #include <asm/syscalls_x32.h>
>  #undef __SYSCALL
>  
> +#undef __SYSCALL_NORETURN
> +#define __SYSCALL_NORETURN __SYSCALL
> +
>  #define __SYSCALL(nr, sym) __x64_##sym,
>  const sys_call_ptr_t x32_sys_call_table[] = {
>  #include <asm/syscalls_x32.h>
> diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
> index 7e8d46f4147f..6695105d21b5 100644
> --- a/arch/x86/entry/syscalls/syscall_64.tbl
> +++ b/arch/x86/entry/syscalls/syscall_64.tbl
> @@ -2,7 +2,7 @@
>  # 64-bit system call numbers and entry vectors
>  #
>  # The format is:
> -# <number> <abi> <name> <entry point>
> +# <number> <abi> <name> <entry point> [0 noreturn]
>  #
>  # The __x64_sys_*() stubs are created on-the-fly for sys_*() system calls
>  #
> @@ -68,7 +68,7 @@
>  57	common	fork			sys_fork
>  58	common	vfork			sys_vfork
>  59	64	execve			sys_execve
> -60	common	exit			sys_exit
> +60	common	exit			sys_exit		0	noreturn
>  61	common	wait4			sys_wait4
>  62	common	kill			sys_kill
>  63	common	uname			sys_newuname
> @@ -239,7 +239,7 @@
>  228	common	clock_gettime		sys_clock_gettime
>  229	common	clock_getres		sys_clock_getres
>  230	common	clock_nanosleep		sys_clock_nanosleep
> -231	common	exit_group		sys_exit_group
> +231	common	exit_group		sys_exit_group		0	noreturn
>  232	common	epoll_wait		sys_epoll_wait
>  233	common	epoll_ctl		sys_epoll_ctl
>  234	common	tgkill			sys_tgkill
> diff --git a/arch/x86/um/sys_call_table_32.c b/arch/x86/um/sys_call_table_32.c
> index 89df5d89d664..c7d4bf955d2b 100644
> --- a/arch/x86/um/sys_call_table_32.c
> +++ b/arch/x86/um/sys_call_table_32.c
> @@ -24,6 +24,7 @@
>  #define __SYSCALL_WITH_COMPAT(nr, native, compat)	__SYSCALL(nr, native)
>  
>  #define __SYSCALL(nr, sym) extern asmlinkage long sym(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
> +#define __SYSCALL_NORETURN __SYSCALL
>  #include <asm/syscalls_32.h>
>  
>  #undef __SYSCALL
> diff --git a/arch/x86/um/sys_call_table_64.c b/arch/x86/um/sys_call_table_64.c
> index b0b4cfd2308c..4760c40ae5cd 100644
> --- a/arch/x86/um/sys_call_table_64.c
> +++ b/arch/x86/um/sys_call_table_64.c
> @@ -19,6 +19,7 @@
>  #define sys_ioperm sys_ni_syscall
>  
>  #define __SYSCALL(nr, sym) extern asmlinkage long sym(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
> +#define __SYSCALL_NORETURN __SYSCALL
>  #include <asm/syscalls_64.h>
>  
>  #undef __SYSCALL
> diff --git a/scripts/syscalltbl.sh b/scripts/syscalltbl.sh
> index 6abe143889ef..16487d47e06a 100755
> --- a/scripts/syscalltbl.sh
> +++ b/scripts/syscalltbl.sh
> @@ -54,7 +54,7 @@ nxt=0
>  
>  grep -E "^[0-9]+[[:space:]]+$abis" "$infile" | {
>  
> -	while read nr abi name native compat ; do
> +	while read nr abi name native compat noreturn; do
>  
>  		if [ $nxt -gt $nr ]; then
>  			echo "error: $infile: syscall table is not sorted or duplicates the same syscall number" >&2
> @@ -66,7 +66,9 @@ grep -E "^[0-9]+[[:space:]]+$abis" "$infile" | {
>  			nxt=$((nxt + 1))
>  		done
>  
> -		if [ -n "$compat" ]; then
> +		if [ -n "$noreturn" ]; then
> +			echo "__SYSCALL_NORETURN($nr, $native)"
> +		elif [ -n "$compat" ]; then
>  			echo "__SYSCALL_WITH_COMPAT($nr, $native, $compat)"
>  		elif [ -n "$native" ]; then
>  			echo "__SYSCALL($nr, $native)"
> diff --git a/tools/objtool/noreturns.h b/tools/objtool/noreturns.h
> index 7ebf29c91184..1e8141ef1b15 100644
> --- a/tools/objtool/noreturns.h
> +++ b/tools/objtool/noreturns.h
> @@ -7,12 +7,16 @@
>   * Yes, this is unfortunate.  A better solution is in the works.
>   */
>  NORETURN(__fortify_panic)
> +NORETURN(__ia32_sys_exit)
> +NORETURN(__ia32_sys_exit_group)
>  NORETURN(__kunit_abort)
>  NORETURN(__module_put_and_kthread_exit)
>  NORETURN(__reiserfs_panic)
>  NORETURN(__stack_chk_fail)
>  NORETURN(__tdx_hypercall_failed)
>  NORETURN(__ubsan_handle_builtin_unreachable)
> +NORETURN(__x64_sys_exit)
> +NORETURN(__x64_sys_exit_group)
>  NORETURN(arch_cpu_idle_dead)
>  NORETURN(bch2_trans_in_restart_error)
>  NORETURN(bch2_trans_restart_error)
> -- 
> 2.44.0
>