Use call via structure only when multiple tracing backends are availableesyr/gdbserver-prep

Since dispatching function calls via the tracing backend structure
definitely imposes some overhead, let's try to minimise it for the
(pretty common) case of having only one tracing backend available.

* configure.ac (additional_tracing_backends): New m4 variable.
(ADDITIONAL_TRACING_BACKENDS): New AC_DEFINE, equal to
additional_tracing_backends.
* ptrace_backend.c: Put ptrace_backend definition under
"#if ADDITIONAL_TRACING_PACKENDS".
* ptrace_backend.h: Put ptrace_backend declaration under
"#if ADDITIONAL_TRACING_PACKENDS".
* tcb_wait_data.h [!ADDITIONAL_TRACING_PACKENDS]: Provide macros for
aliasing trace_wait_data_size, init_trace_wait_data,
copy_trace_wait_data, and free_trace_wait_data to ptrace-based tracing
backend definitions.
* tracing_backend.c: Put the contents, except local_open, under #if
ADDITIONAL_TRACING_PACKENDS.
* tracing_backend.h: Put the contents (except local_open) under #if
ADDITIONAL_TRACING_PACKENDS, provide macros for all the inline functions
that alias them to the respective functions in the ptrace-based tracing
backend in the opposite case.

6 files changed, 103 insertions, 4 deletions

diff --git a/configure.ac b/configure.ac
index 9bf64c339..28fc714dc 100644
--- a/configure.ac
+++ b/configure.ac
@@ -48,6 +48,8 @@ AC_SUBST([COPYRIGHT_YEAR], [copyright_year])
 AC_DEFINE([MANPAGE_DATE], "[manpage_date]", [Date])
 AC_SUBST([MANPAGE_DATE], [manpage_date])
 
+m4_define([additional_tracing_backends], [0])
+
 AC_MSG_CHECKING([for supported architecture])
 arch_m32=
 arch_mx32=
@@ -916,6 +918,9 @@ st_MPERS([mx32], [x86_64])
 AX_VALGRIND_DFLT([sgcheck], [off])
 AX_VALGRIND_CHECK
 
+AC_DEFINE([ADDITIONAL_TRACING_BACKENDS], additional_tracing_backends,
+          [Whether additional tracing backends are available])
+
 AC_CONFIG_FILES([Makefile
 		 tests/Makefile
 		 tests-m32/Makefile
diff --git a/ptrace_backend.c b/ptrace_backend.c
index 06ce89dec..173969036 100644
--- a/ptrace_backend.c
+++ b/ptrace_backend.c
@@ -12,6 +12,8 @@
 #include "ptrace_backend.h"
 #include "ptrace_wait_data.h"
 
+#if ADDITIONAL_TRACING_BACKENDS
+
 const struct tracing_backend ptrace_backend = {
 	.name                    = "ptrace",
 
@@ -60,3 +62,5 @@ const struct tracing_backend ptrace_backend = {
 	.sendmsg                 = local_sendmsg,
 	.recvmsg                 = local_recvmsg,
 };
+
+#endif /* ADDITIONAL_TRACING_BACKENDS */
diff --git a/ptrace_backend.h b/ptrace_backend.h
index 3e28c487c..4e32f44e9 100644
--- a/ptrace_backend.h
+++ b/ptrace_backend.h
@@ -49,6 +49,10 @@ extern int ptrace_upeek(struct tcb *tcp, unsigned long off,
 			kernel_ulong_t *res);
 extern int ptrace_upoke(struct tcb *tcp, unsigned long off, kernel_ulong_t val);
 
+#if ADDITIONAL_TRACING_BACKENDS
+
 extern const struct tracing_backend ptrace_backend;
 
+#endif /* ADDITIONAL_TRACING_BACKENDS */
+
 #endif /* !STRACE_PTRACE_BACKEND_H */
diff --git a/tcb_wait_data.h b/tcb_wait_data.h
index acc4e899c..dc26e6d8c 100644
--- a/tcb_wait_data.h
+++ b/tcb_wait_data.h
@@ -28,6 +28,8 @@ struct tcb_wait_data {
 	siginfo_t si;        /**< siginfo, returned by PTRACE_GETSIGINFO */
 };
 
+#if ADDITIONAL_TRACING_BACKENDS
+
 static inline size_t
 trace_wait_data_size(struct tcb *tcp)
 {
@@ -74,4 +76,15 @@ free_trace_wait_data(struct tcb_wait_data *wd)
 	}
 }
 
+#else /* !ADDITIONAL_TRACING_BACKENDS */
+
+# include "ptrace_wait_data.h"
+
+# define trace_wait_data_size(tcp_)  sizeof(struct ptrace_wait_data)
+# define init_trace_wait_data        ptrace_init_trace_wait_data
+# define copy_trace_wait_data        ptrace_copy_trace_wait_data
+# define free_trace_wait_data        ptrace_free_trace_wait_data
+
+#endif /* ADDITIONAL_TRACING_BACKENDS */
+
 #endif /* !STRACE_TCB_WAIT_DATA_H */
diff --git a/tracing_backend.c b/tracing_backend.c
index 858bd586f..86aebac86 100644
--- a/tracing_backend.c
+++ b/tracing_backend.c
@@ -9,19 +9,25 @@
 
 #include "defs.h"
 
-#include <assert.h>
 #include <fcntl.h>
+
+#include <sys/stat.h>
+#include <sys/types.h>
+
+#include "tracing_backend.h"
+
+
+#if ADDITIONAL_TRACING_BACKENDS
+
+#include <assert.h>
 #include <limits.h>
 #include <signal.h>
 #include <stdlib.h>
 #include <unistd.h>
 
 #include <sys/socket.h>
-#include <sys/stat.h>
-#include <sys/types.h>
 #include <sys/xattr.h>
 
-#include "tracing_backend.h"
 #include "ptrace_backend.h"
 
 /* Tracing backeng management functions */
@@ -164,3 +170,5 @@ local_recvmsg(struct tcb *tcp, int fd, struct msghdr *msg, int flags)
 {
 	return recvmsg(fd, msg, flags);
 }
+
+#endif  /* ADDITIONAL_TRACING_BACKENDS */
diff --git a/tracing_backend.h b/tracing_backend.h
index 8140ae4fd..3e00b4326 100644
--- a/tracing_backend.h
+++ b/tracing_backend.h
@@ -14,6 +14,7 @@
 
 #include "trace_event.h"
 
+
 #if defined IN_MPERS || defined IN_MPERS_BOOTSTRAP
 typedef int strace_stat_t;
 #else
@@ -22,6 +23,8 @@ typedef int strace_stat_t;
 strace_stat_t;
 #endif
 
+#if ADDITIONAL_TRACING_BACKENDS
+
 struct msghdr;
 
 
@@ -482,4 +485,66 @@ tracee_recvmsg(struct tcb *tcp, int fd, struct msghdr *msg, int flags)
 	return error_set_errno(ENOSYS);
 }
 
+#else /* !ADDITIONAL_TRACING_BACKENDS */
+
+# include "ptrace_backend.h"
+
+# define tracing_backend_name()      "ptrace"
+# define tracing_backend_handle_arg(a_, o_) false
+# define tracing_backend_init        ptrace_init
+# define tracing_backend_post_init() ((void) 0)
+# define tracing_backend_cleanup(s_) ((void) 0)
+
+# define startup_child               ptrace_startup_child
+# define attach_tcb                  ptrace_attach_tcb
+# define detach                      ptrace_detach
+
+# define next_event                  ptrace_next_event
+# define handle_group_stop           ptrace_handle_group_stop
+# define handle_exec                 ptrace_handle_exec
+# define restart_process             ptrace_restart_process
+
+# define clear_regs                  ptrace_clear_regs
+# define get_regs                    ptrace_get_regs
+# define get_scno                    ptrace_get_scno
+# define set_scno                    ptrace_set_scno
+# define set_error                   ptrace_set_error
+# define set_success                 ptrace_set_success
+# define get_instruction_pointer     ptrace_get_instruction_pointer
+# define get_stack_pointer           ptrace_get_stack_pointer
+# define get_syscall_args            ptrace_get_syscall_args
+# define get_syscall_result          ptrace_get_syscall_result
+
+# define umoven                      ptrace_umoven
+# define umovestr                    ptrace_umovestr
+# define upeek                       ptrace_upeek
+# define upoke                       ptrace_upoke
+
+# define tracee_kill(tcp_, sig_) \
+	kill((tcp_)->pid, (sig_))
+# define tracee_realpath(tcp_, path_, resolved_path_) \
+	realpath((path_), (resolved_path_))
+# define tracee_open(tcp_, path_, flags_, mode_) \
+	open_file((path_), (flags_), (mode_))
+# define tracee_pread(tcp_, fd_, buf_, count_, offset_) \
+	pread((fd_), (buf_), (count_), (offset_))
+# define tracee_close(tcp_, fd_) \
+	close(fd_)
+# define tracee_readlink(tcp_, path_, buf_, buf_size_) \
+	readlink((path_), (buf_), (buf_size_))
+# define tracee_stat(tcp_, path_, buf_) \
+	stat_file((path_), (buf_))
+# define tracee_fstat(tcp_, fd_, buf_) \
+	fstat_file((fd_), (buf_))
+# define tracee_getxattr(tcp_, path_, name_, buf_, buf_size_) \
+	getxattr((path_), (name_), (buf_), (buf_size_))
+# define tracee_socket(tcp_, domain_, type_, protocol_) \
+	socket((domain_), (type_), (protocol_))
+# define tracee_sendmsg(tcp_, fd_, msg_, flags_) \
+	sendmsg((fd_), (msg_), (flags_))
+# define tracee_recvmsg(tcp_, fd_, msg_, flags_) \
+	recvmsg((fd_), (msg_), (flags_))
+
+#endif /* !ADDITIONAL_TRACING_BACKENDS */
+
 #endif /* !STRACE_TRACING_BACKEND_H */