[PATCH v2 2/3] Stage output for -z and -Z options
Paul Chaignon
paul.chaignon at gmail.com
Tue Apr 2 19:57:04 UTC 2019
The -z and -Z options print only successful and failing syscalls
respectively. However, failure of syscall is only known after syscall
return. Thus, we end up with something like this on, e.g., ENOENT:
open("does_not_exist", O_RDONLY <unfinished ...>
whereas the intended result is that the open(...) line is not shown at
all.
This patch fixes this issue using open_memstream. When either the -z or
the -Z option is used, the output is staged in memory (using
open_memstream) until we know whether the syscall was successful. If the
open_memstream function is not available, strace retains the old behavior.
Signed-off-by: Paul Chaignon <paul.chaignon at gmail.com>
Co-Authored-by: Burkhard Kohl <burkhard.kohl at intel.com>
---
Makefile.am | 1 +
configure.ac | 1 +
defs.h | 15 ++++++++++
stage_output.c | 74 ++++++++++++++++++++++++++++++++++++++++++++++++++
strace.c | 62 ++++++++++++++++++++++++++++++++++++------
syscall.c | 19 +++++++------
6 files changed, 155 insertions(+), 17 deletions(-)
create mode 100644 stage_output.c
diff --git a/Makefile.am b/Makefile.am
index 56987ae0..dd44b04c 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -298,6 +298,7 @@ strace_SOURCES = \
sock.c \
sockaddr.c \
socketutils.c \
+ stage_output.c \
sparc.c \
sram_alloc.c \
stat.c \
diff --git a/configure.ac b/configure.ac
index c95fd229..91f3152d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -258,6 +258,7 @@ AC_CHECK_FUNCS(m4_normalize([
iconv_open
if_indextoname
open64
+ open_memstream
prctl
preadv
process_vm_readv
diff --git a/defs.h b/defs.h
index b5ebb343..8600dec2 100644
--- a/defs.h
+++ b/defs.h
@@ -204,6 +204,12 @@ struct tcb {
int sys_func_rval; /* Syscall entry parser's return value */
int curcol; /* Output column for this process */
FILE *outf; /* Output file for this process */
+#if HAVE_OPEN_MEMSTREAM
+ FILE *memf; /* Staged output file for this process */
+ char *memfptr;
+ size_t memfloc;
+#endif
+
const char *auxstr; /* Auxiliary info from syscall (see RVAL_STR) */
void *_priv_data; /* Private data for syscall decoding functions */
void (*_free_priv_data)(void *); /* Callback for freeing priv_data */
@@ -418,6 +424,8 @@ extern bool count_wallclock;
extern unsigned int qflag;
extern bool not_failing_only;
extern bool failing_only;
+/* allows dropping of failed/successful syscalls output */
+extern bool stage_output;
extern unsigned int show_fd_path;
/* are we filtering traces based on paths? */
extern struct path_set {
@@ -1165,6 +1173,13 @@ extern void tprints(const char *str);
extern void tprintf_comment(const char *fmt, ...) ATTRIBUTE_FORMAT((printf, 1, 2));
extern void tprints_comment(const char *str);
+/*
+ * Staging output for -z/-Z (not_failing_only/failing_only).
+ */
+extern FILE *strace_openmemstream(struct tcb *tcp);
+extern void drop_staged_out(struct tcb *tcp);
+extern void publish_staged_out(struct tcb *tcp);
+
static inline void
printaddr_comment(const kernel_ulong_t addr)
{
diff --git a/stage_output.c b/stage_output.c
new file mode 100644
index 00000000..81b29b31
--- /dev/null
+++ b/stage_output.c
@@ -0,0 +1,74 @@
+/*
+ * Copyright (c) 2017 Burkhard Kohl <burkhard.kohl at intel.com>
+ * Copyright (c) 2019 Paul Chaignon <paul.chaignon at gmail.com>
+ * All rights reserved.
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ */
+
+/*
+ * Output staging is based on the "open_memstream()" function, see:
+ * http://man7.org/linux/man-pages/man3/open_memstream.3.html
+ * Requires glibc version 2.7 mininal
+ *
+ * open_memstream returns a FILE stream that allows writing to a
+ * dynamically growing buffer, that can be either copied to
+ * tcp->outf (syscall successful) or dropped (syscall failed)
+ */
+
+#include "defs.h"
+#if HAVE_OPEN_MEMSTREAM
+
+FILE *
+strace_openmemstream(struct tcb *tcp)
+{
+ FILE *fp = NULL;
+
+ tcp->memfptr = NULL;
+ fp = open_memstream(&tcp->memfptr, &tcp->memfloc);
+ if (!fp)
+ perror_msg_and_die("open_memstream");
+ /* Call to fflush required to update tcp->memfptr, see open_memstream
+ * man page. */
+ fflush(fp);
+ tcp->memf = fp;
+ return fp;
+}
+
+void
+drop_staged_out(struct tcb *tcp)
+{
+ if (!tcp->memf)
+ return;
+
+ if (fclose(tcp->memf))
+ perror_msg("fclose(tcp->memf)");
+ if (tcp->memfptr) {
+ if (debug_flag)
+ error_msg("syscall output dropped: %s", tcp->memfptr);
+ free(tcp->memfptr);
+ tcp->memfptr = NULL;
+ }
+
+ /* reopen tcp->memf for subsequent use */
+ strace_openmemstream(tcp);
+}
+
+void
+publish_staged_out(struct tcb *tcp)
+{
+ if (!tcp->memf)
+ return;
+
+ if (fclose(tcp->memf))
+ perror_msg("flose(tcp->memf)");
+ if (tcp->memfptr) {
+ fprintf(tcp->outf, "%s", tcp->memfptr);
+ free(tcp->memfptr);
+ tcp->memfptr = NULL;
+ }
+
+ /* reopen tcp->memf for subsequent use */
+ strace_openmemstream(tcp);
+}
+#endif
diff --git a/strace.c b/strace.c
index bd2dd992..8c5eeb30 100644
--- a/strace.c
+++ b/strace.c
@@ -112,6 +112,7 @@ static int post_attach_sigstop = TCB_IGNORE_ONE_SIGSTOP;
/* Sometimes we want to print succeeding/failing syscalls only. */
bool not_failing_only;
bool failing_only;
+bool stage_output;
/* Show path associated with fd arguments */
unsigned int show_fd_path;
@@ -275,7 +276,13 @@ Filtering:\n\
-e expr a qualifying expression: option=[!]all or option=[!]val1[,val2]...\n\
options: trace, abbrev, verbose, raw, signal, read, write, fault, inject, kvm\n\
-P path trace accesses to path\n\
-\n\
+"
+#if HAVE_OPEN_MEMSTREAM
+" -z print only succeeding syscalls\n\
+ -Z print only failing syscalls\n\
+"
+#endif
+"\n\
Tracing:\n\
-b execve detach on execve syscall\n\
-D run tracer process as a detached grandchild, not as parent\n\
@@ -303,10 +310,6 @@ Miscellaneous:\n\
/* ancient, no one should use it
-F -- attempt to follow vforks (deprecated, use -f)\n\
*/
-/* this is broken, so don't document it
--z -- print only succeeding syscalls\n\
--Z -- print only failing syscalls\n\
- */
, DEFAULT_ACOLUMN, DEFAULT_STRLEN, DEFAULT_SORTBY);
exit(0);
}
@@ -512,8 +515,17 @@ ATTRIBUTE_FORMAT((printf, 1, 0))
static void
tvprintf(const char *const fmt, va_list args)
{
+ int n = 0;
if (current_tcp) {
- int n = vfprintf(current_tcp->outf, fmt, args);
+ /* If open_memstream is not supported, stage_output will always
+ * be false. */
+ if (stage_output) {
+ if (!current_tcp->memf)
+ error_msg_and_die("No file opened for current_tcp->memf\n");
+ n = vfprintf(current_tcp->memf, fmt, args);
+ } else
+ n = vfprintf(current_tcp->outf, fmt, args);
+
if (n < 0) {
/* very unlikely due to vfprintf buffering */
outf_perror(current_tcp);
@@ -539,7 +551,18 @@ void
tprints(const char *str)
{
if (current_tcp) {
- int n = fputs_unlocked(str, current_tcp->outf);
+ int n;
+
+ /* If open_memstream is not supported, stage_output will always
+ * be false. */
+ if (stage_output) {
+ if (!current_tcp->memf)
+ error_msg_and_die("No file opened for current_tcp->memf\n");
+ n = fputs_unlocked(str, current_tcp->memf);
+ } else {
+ n = fputs_unlocked(str, current_tcp->outf);
+ }
+
if (n >= 0) {
current_tcp->curcol += strlen(str);
return;
@@ -700,6 +723,11 @@ after_successful_attach(struct tcb *tcp, const unsigned int flags)
tcp->outf = strace_fopen(name);
}
+#if HAVE_OPEN_MEMSTREAM
+ if (not_failing_only || failing_only)
+ strace_openmemstream(tcp);
+#endif
+
#ifdef ENABLE_STACKTRACE
if (stack_trace_enabled)
unwind_tcb_init(tcp);
@@ -1563,6 +1591,9 @@ init(int argc, char *argv[])
int c, i;
int optF = 0;
+ /* during init don't print to internal memf stream */
+ stage_output = false;
+
if (!program_invocation_name || !*program_invocation_name) {
static char name[] = "strace";
program_invocation_name =
@@ -1782,6 +1813,10 @@ init(int argc, char *argv[])
unwind_init();
#endif
+#ifdef HAVE_OPEN_MEMSTREAM
+ stage_output = not_failing_only || failing_only;
+#endif
+
/* See if they want to run as another user. */
if (username != NULL) {
struct passwd *pent;
@@ -2108,6 +2143,10 @@ print_signalled(struct tcb *tcp, const int pid, int status)
static void
print_exited(struct tcb *tcp, const int pid, int status)
{
+ bool saved_stage_output_flag = stage_output;
+
+ stage_output = false;
+
if (pid == strace_child) {
exit_code = WEXITSTATUS(status);
strace_child = 0;
@@ -2119,11 +2158,16 @@ print_exited(struct tcb *tcp, const int pid, int status)
tprintf("+++ exited with %d +++\n", WEXITSTATUS(status));
line_ended();
}
+
+ stage_output = saved_stage_output_flag;
}
static void
print_stopped(struct tcb *tcp, const siginfo_t *si, const unsigned int sig)
{
+ bool saved_stage_output_flag = stage_output;
+ stage_output = false;
+
if (cflag != CFLAG_ONLY_STATS
&& !hide_log(tcp)
&& is_number_in_set(sig, signal_set)) {
@@ -2141,6 +2185,8 @@ print_stopped(struct tcb *tcp, const siginfo_t *si, const unsigned int sig)
unwind_tcb_print(tcp);
#endif
}
+
+ stage_output = saved_stage_output_flag;
}
static void
@@ -2793,7 +2839,7 @@ static void ATTRIBUTE_NORETURN
terminate(void)
{
int sig = interrupted;
-
+ stage_output = false;
cleanup(sig);
if (cflag)
call_summary(shared_log);
diff --git a/syscall.c b/syscall.c
index 7ea45292..3b4d3b44 100644
--- a/syscall.c
+++ b/syscall.c
@@ -753,18 +753,17 @@ syscall_exiting_trace(struct tcb *tcp, struct timespec *ts, int res)
if (raw(tcp)) {
/* sys_res = printargs(tcp); - but it's nop on sysexit */
} else {
- /* FIXME: not_failing_only (IOW, option -z) is broken:
- * failure of syscall is known only after syscall return.
- * Thus we end up with something like this on, say, ENOENT:
- * open("does_not_exist", O_RDONLY <unfinished ...>
- * {next syscall decode}
- * whereas the intended result is that open(...) line
- * is not shown at all.
- */
if ((not_failing_only && syserror(tcp)) ||
- (failing_only && !syserror(tcp)))
+ (failing_only && !syserror(tcp))) {
+ /* If open_memstream is not supported, stage_output
+ * will always be false. */
+ if (stage_output) {
+ drop_staged_out(tcp);
+ line_ended();
+ }
return 0; /* ignore failed/successful
* syscalls */
+ }
if (tcp->sys_func_rval & RVAL_DECODED)
sys_res = tcp->sys_func_rval;
else
@@ -900,6 +899,8 @@ syscall_exiting_trace(struct tcb *tcp, struct timespec *ts, int res)
}
tprints("\n");
dumpio(tcp);
+ if (stage_output)
+ publish_staged_out(tcp);
line_ended();
#ifdef ENABLE_STACKTRACE
--
2.17.1
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