x86 ptrace: unify syscall tracing

This unifies and cleans up the syscall tracing code on i386 and x86_64.

Using a single function for entry and exit tracing on 32-bit made the
do_syscall_trace() into some terrible spaghetti.  The logic is clear and
simple using separate syscall_trace_enter() and syscall_trace_leave()
functions as on 64-bit.

The unification adds PTRACE_SYSEMU and PTRACE_SYSEMU_SINGLESTEP support
on x86_64, for 32-bit ptrace() callers and for 64-bit ptrace() callers
tracing either 32-bit or 64-bit tasks.  It behaves just like 32-bit.

Changing syscall_trace_enter() to return the syscall number shortens
all the assembly paths, while adding the SYSEMU feature in a simple way.

Signed-off-by: Roland McGrath <roland@redhat.com>

1 files changed, 9 insertions, 5 deletions

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index ae63e584c34..63001c6ecf6 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -349,8 +349,7 @@ ENTRY(system_call_after_swapgs)
         movq  %rcx,RIP-ARGOFFSET(%rsp)
         CFI_REL_OFFSET rip,RIP-ARGOFFSET
         GET_THREAD_INFO(%rcx)
-        testl $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SECCOMP), \
-                TI_flags(%rcx)
+        testl $_TIF_WORK_SYSCALL_ENTRY,TI_flags(%rcx)
         jnz tracesys
         cmpq $__NR_syscall_max,%rax
         ja badsys
@@ -430,7 +429,12 @@ tracesys:
         FIXUP_TOP_OF_STACK %rdi
         movq %rsp,%rdi
         call syscall_trace_enter
-        LOAD_ARGS ARGOFFSET  /* reload args from stack in case ptrace changed it */
+        /*
+         * Reload arg registers from stack in case ptrace changed them.
+         * We don't reload %rax because syscall_trace_enter() returned
+         * the value it wants us to use in the table lookup.
+         */
+        LOAD_ARGS ARGOFFSET, 1
         RESTORE_REST
         cmpq $__NR_syscall_max,%rax
         ja   int_ret_from_sys_call      /* RAX(%rsp) set to -ENOSYS above */
@@ -483,7 +487,7 @@ int_very_careful:
         ENABLE_INTERRUPTS(CLBR_NONE)
         SAVE_REST
         /* Check for syscall exit trace */      
-        testl $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SINGLESTEP),%edx
+        testl $_TIF_WORK_SYSCALL_EXIT,%edx
         jz int_signal
         pushq %rdi
         CFI_ADJUST_CFA_OFFSET 8
@@ -491,7 +495,7 @@ int_very_careful:
         call syscall_trace_leave
         popq %rdi
         CFI_ADJUST_CFA_OFFSET -8
-        andl $~(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SINGLESTEP),%edi
+        andl $~(_TIF_WORK_SYSCALL_EXIT|_TIF_SYSCALL_EMU),%edi
         jmp int_restore_rest
         
 int_signal: