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SubjectRe: [BUG] objtool complains about missing __noreturn__ on x64_sys_call() and ia32_sys_call()
On Thu, Apr 18, 2024 at 05:22:26PM -0700, Paul E. McKenney wrote:
> Hello!
>
> Recent -next kernels, including next-20240418, get the following objtool
> build errors:
>
> 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
>
> These functions appear to have been added to -next and mainline by
> commit 1e3ad78334a6 ("x86/syscall: Don't force use of indirect calls
> for system calls"). But the diagnostic does not make much sense because
> both functions always return unless the system call itself doesn't return.

These warnings are (perhaps confusingly yet still correctly) calling out
the fact that the exit syscalls __x64_sys_exit() and
__ia32_sys_exit_group() don't return but are not annotated as such.

It probably doesn't matter much for syscalls and I could get objtool to
just ignore such scenarios.

Or we could actually annotate them as __noreturn. Does this fix it?


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..f99e9e4ad671 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -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/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)
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