On Thu, Nov 27, 2014 at 06:46:29AM +0000, AKASHI Takahiro wrote:
On 11/26/2014 10:02 PM, Will Deacon wrote:
On Wed, Nov 26, 2014 at 04:49:47AM +0000, AKASHI Takahiro wrote:
If tracer modifies a syscall number to -1, this traced system call should be skipped with a return value specified in x0. This patch implements this semantics.
Please note:
- syscall entry tracing and syscall exit tracing (ftrace tracepoint and audit) are always executed, if enabled, even when skipping a system call (that is, -1). In this way, we can avoid a potential bug where audit_syscall_entry() might be called without audit_syscall_exit() at the previous system call being called, that would cause OOPs in audit_syscall_entry().
Signed-off-by: AKASHI Takahiro takahiro.akashi@linaro.org
arch/arm64/kernel/entry.S | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 726b910..946ec52 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -161,6 +161,7 @@ */ sc_nr .req x25 // number of system calls scno .req x26 // syscall number +scno_w .req w26 // syscall number (lower 32 bits) stbl .req x27 // syscall table pointer tsk .req x28 // current thread_info
@@ -668,8 +669,14 @@ ENDPROC(el0_svc) * switches, and waiting for our parent to respond. */ __sys_trace:
- mov x0, sp
- cmp scno_w, #-1 // set default errno for
I hate that we have to use scno_w, but the only alternative I can think of is using w8 directly, which isn't any better and doesn't work for compat. Ho-hum, I guess we'll stick with what you have.
The possible approaches might be:
- use 32-bit registers for scno & sc_nr and use "sxtw scno, w8," or
- use an extra reg like __sys_trace: mov x0, #0xffffffff
or even better: mov w0, #-1
cmp scno, x0 b.ne 1f
Good thinking, I prefer that.
Will