Straighten up confused comments/messages about post-execve SIGTRAP handling
* defs.h: Explain TCB_INSYSCALL and TCB_WAITEXECVE bits in detail.
* strace.c (choose_pfd): Use entering/exiting macros instead of direct check
for TCB_INSYSCALL.
* syscall.c (get_scno): Use entering/exiting macros instead of direct check
for TCB_INSYSCALL. Fix comments about post-execve SIGTRAP.
(syscall_fixup): Use entering/exiting instead of direct check
for TCB_INSYSCALL. Add a comment what "not a syscall entry" message
usually means. Change wrong "stray syscall exit" messages into
"not a syscall entry" ones.
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
diff --git a/defs.h b/defs.h
index c4ea5fa..97dbf6a 100644
--- a/defs.h
+++ b/defs.h
@@ -432,7 +432,25 @@
/* TCB flags */
#define TCB_STARTUP 00001 /* We have just begun ptracing this process */
#define TCB_INUSE 00002 /* This table entry is in use */
-#define TCB_INSYSCALL 00004 /* A system call is in progress */
+/*
+ * Are we in system call entry or in syscall exit?
+ *
+ * This bit is set after all syscall entry processing is done.
+ * Therefore, this bit will be set when next ptrace stop occurs,
+ * which should be syscall exit stop. Other stops which are possible
+ * directly after syscall entry (death, ptrace event stop)
+ * are simpler and handled without calling trace_syscall(), therefore
+ * the places where TCB_INSYSCALL can be set but we aren't in syscall stop
+ * are limited to trace(), this condition is never observed in trace_syscall()
+ * and below.
+ * The bit is cleared after all syscall exit processing is done.
+ * User-generated SIGTRAPs and post-execve SIGTRAP make it necessary
+ * to be very careful and NOT set TCB_INSYSCALL bit when they are encountered.
+ * TCB_WAITEXECVE bit is used for this purpose (see below).
+ *
+ * Use entering(tcp) / exiting(tcp) to check this bit to make code more readable.
+ */
+#define TCB_INSYSCALL 00004
#define TCB_ATTACHED 00010 /* Process is not our own child */
#ifdef LINUX
#define TCB_ATTACH_DONE 00020 /* PTRACE_ATTACH was done on this tcb->pid */
@@ -443,14 +461,17 @@
#define TCB_FILTERED 02000 /* This system call has been filtered out */
#ifdef LINUX
/* x86 does not need TCB_WAITEXECVE.
- * It can detect execve's SIGTRAP by looking at eax/rax.
- * See "stray syscall exit: eax = " message in syscall_fixup().
+ * It can detect SIGTRAP by looking at eax/rax.
+ * See "not a syscall entry (eax = %ld)\n" message in syscall_fixup().
*/
# if defined(ALPHA) || defined(AVR32) || defined(SPARC) || defined(SPARC64) \
|| defined(POWERPC) || defined(IA64) || defined(HPPA) \
|| defined(SH) || defined(SH64) || defined(S390) || defined(S390X) \
|| defined(ARM) || defined(MIPS) || defined(BFIN) || defined(TILE)
-# define TCB_WAITEXECVE 04000 /* ignore SIGTRAP after execve */
+/* This tracee has entered into execve syscall. Expect post-execve SIGTRAP
+ * to happen. (When it is detected, tracee is continued and this bit is cleared.)
+ */
+# define TCB_WAITEXECVE 04000
# endif
# include <sys/syscall.h>
# ifndef __NR_exit_group