Commit 1014c81d authored by AKASHI Takahiro's avatar AKASHI Takahiro Committed by Will Deacon

arm64: ptrace: allow tracer to skip a system call

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: default avatarAKASHI Takahiro <>
[will: fixed up conflict with blr rework]
Signed-off-by: default avatarWill Deacon <>
parent 766a85d7
......@@ -669,8 +669,15 @@ ENDPROC(el0_svc)
* switches, and waiting for our parent to respond.
mov x0, sp
mov w0, #-1 // set default errno for
cmp scno, x0 // user-issued syscall(-1) 1f
mov x0, #-ENOSYS
str x0, [sp, #S_X0]
1: mov x0, sp
bl syscall_trace_enter
cmp w0, #-1 // skip the syscall?
b.eq __sys_trace_return_skipped
uxtw scno, w0 // syscall number (possibly new)
mov x1, sp // pointer to regs
cmp scno, sc_nr // check upper syscall limit
......@@ -683,7 +690,8 @@ __sys_trace:
blr x16 // call sys_* routine
str x0, [sp] // save returned x0
str x0, [sp, #S_X0] // save returned x0
mov x0, sp
bl syscall_trace_exit
b ret_to_user
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