[PATCH v5 2/4] Stage output for -z and -Z options
Paul Chaignon
paul.chaignon at gmail.com
Fri Jun 28 09:34:02 UTC 2019
-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 the syscall return status. If the
open_memstream function is not available, these new options error out.
* stage_output.c: New file.
* defs.h (tcb): Add real_outf, memfptr, memfloc fields for memstream.
(strace_open_memstream): New prototype.
(strace_close_memstream): New prototype.
* Makefile.am: Add stage_output.c.
* configure.ac: Add open_memstream.
* strace.1.in: Document -z and -Z options.
* strace.c (init): Error on -z and -Z options if open_memstream if
unavailable.
(maybe_switch_tcbs): Handle switch of memstream between tcbs.
* syscall.c (syscall_entering_trace): Open memstream.
(syscall_exiting_trace): Filter failed syscalls if failing_only is set,
handle raw(tcp) case.
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 | 10 ++++++++
stage_output.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++
strace.1.in | 6 +++++
strace.c | 28 ++++++++++++++++++----
syscall.c | 25 ++++++++++----------
7 files changed, 118 insertions(+), 17 deletions(-)
create mode 100644 stage_output.c
diff --git a/Makefile.am b/Makefile.am
index a8ace321..ec94d2c4 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -309,6 +309,7 @@ strace_SOURCES = \
socketutils.c \
sparc.c \
sram_alloc.c \
+ stage_output.c \
stat.c \
stat.h \
stat64.c \
diff --git a/configure.ac b/configure.ac
index 621312ac..a5286378 100644
--- a/configure.ac
+++ b/configure.ac
@@ -262,6 +262,7 @@ 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 ca458d40..b9b394ec 100644
--- a/defs.h
+++ b/defs.h
@@ -204,6 +204,10 @@ 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 */
+ FILE *real_outf; /* Backup for real outf while staging */
+ char *memfptr;
+ size_t memfloc;
+
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 */
@@ -1196,6 +1200,12 @@ 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 status qualifier.
+ */
+extern FILE *strace_open_memstream(struct tcb *tcp);
+extern void strace_close_memstream(struct tcb *tcp, bool publish);
+
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..971714b7
--- /dev/null
+++ b/stage_output.c
@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2017 Intel Corporation
+ * Copyright (c) 2019 Paul Chaignon <paul.chaignon at gmail.com>
+ * All rights reserved.
+ *
+ * SPDX-License-Identifier: LGPL-2.1-or-later
+ */
+
+/*
+ * 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"
+
+FILE *
+strace_open_memstream(struct tcb *tcp)
+{
+ FILE *fp = NULL;
+
+#if HAVE_OPEN_MEMSTREAM
+ 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);
+
+ /* Store the FILE pointer for later restauration. */
+ tcp->real_outf = tcp->outf;
+ tcp->outf = fp;
+#endif
+
+ return fp;
+}
+
+void
+strace_close_memstream(struct tcb *tcp, bool publish)
+{
+#if HAVE_OPEN_MEMSTREAM
+ if (!tcp->real_outf) {
+ debug_msg("memstream already closed");
+ return;
+ }
+
+ if (fclose(tcp->outf))
+ perror_msg("fclose(tcp->outf)");
+
+ tcp->outf = tcp->real_outf;
+ tcp->real_outf = NULL;
+ if (tcp->memfptr) {
+ if (publish)
+ fputs_unlocked(tcp->memfptr, tcp->outf);
+ else
+ debug_msg("syscall output dropped: %s", tcp->memfptr);
+ free(tcp->memfptr);
+ tcp->memfptr = NULL;
+ }
+#endif
+}
diff --git a/strace.1.in b/strace.1.in
index 76a74119..e1090a0f 100644
--- a/strace.1.in
+++ b/strace.1.in
@@ -771,6 +771,12 @@ Print unabbreviated versions of environment, stat, termios, etc.
calls. These structures are very common in calls and so the default
behavior displays a reasonable subset of structure members. Use
this option to get all of the gory details.
+.TP
+.B \-z
+Print only syscalls that returned without an error code.
+.TP
+.B \-Z
+Print only syscalls that returned with an error code.
.SS Tracing
.TP 12
.BI "\-b " syscall
diff --git a/strace.c b/strace.c
index 24ddd53d..cb1d1840 100644
--- a/strace.c
+++ b/strace.c
@@ -275,6 +275,8 @@ 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\
+ -z print only syscalls that returned without an error code\n\
+ -Z print only syscalls that returned with an error code\n\
\n\
Tracing:\n\
-b execve detach on execve syscall\n\
@@ -303,10 +305,6 @@ 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);
}
@@ -1765,6 +1763,11 @@ init(int argc, char *argv[])
error_msg("-%c has no effect with -c", 'y');
}
+#ifndef HAVE_OPEN_MEMSTREAM
+ if (not_failing_only || failing_only)
+ error_msg_and_help("open_memstream is required to use -z or -Z");
+#endif
+
acolumn_spaces = xmalloc(acolumn + 1);
memset(acolumn_spaces, ' ', acolumn);
acolumn_spaces[acolumn] = '\0';
@@ -2059,10 +2062,25 @@ maybe_switch_tcbs(struct tcb *tcp, const int pid)
fprintf(execve_thread->outf, " <pid changed to %d ...>\n", pid);
/*execve_thread->curcol = 0; - no need, see code below */
}
- /* Swap output FILEs (needed for -ff) */
+ /* Swap output FILEs and memstream (needed for -ff) */
fp = execve_thread->outf;
execve_thread->outf = tcp->outf;
tcp->outf = fp;
+ if (execve_thread->real_outf || tcp->real_outf) {
+ char *memfptr;
+ size_t memfloc;
+
+ fp = execve_thread->real_outf;
+ execve_thread->real_outf = tcp->real_outf;
+ tcp->real_outf = fp;
+ memfptr = execve_thread->memfptr;
+ execve_thread->memfptr = tcp->memfptr;
+ tcp->memfptr = memfptr;
+ memfloc = execve_thread->memfloc;
+ execve_thread->memfloc = tcp->memfloc;
+ tcp->memfloc = memfloc;
+ }
+
/* And their column positions */
execve_thread->curcol = tcp->curcol;
tcp->curcol = 0;
diff --git a/syscall.c b/syscall.c
index 29dfb7a7..4121b7ae 100644
--- a/syscall.c
+++ b/syscall.c
@@ -656,6 +656,9 @@ syscall_entering_trace(struct tcb *tcp, unsigned int *sig)
}
#endif
+ if (not_failing_only || failing_only)
+ strace_open_memstream(tcp);
+
printleader(tcp);
tprintf("%s(", tcp_sysent(tcp)->sys_name);
int res = raw(tcp) ? printargs(tcp) : tcp_sysent(tcp)->sys_func(tcp);
@@ -757,24 +760,22 @@ 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)))
- return 0; /* ignore failed/successful
- * syscalls */
if (tcp->sys_func_rval & RVAL_DECODED)
sys_res = tcp->sys_func_rval;
else
sys_res = tcp_sysent(tcp)->sys_func(tcp);
}
+ if ((not_failing_only && syserror(tcp)) ||
+ (failing_only && !syserror(tcp))) {
+ strace_close_memstream(tcp, false);
+ line_ended();
+ return 0; /* ignore failed/successful
+ * syscalls */
+ } else if (not_failing_only || failing_only) {
+ strace_close_memstream(tcp, true);
+ }
+
tprints(") ");
tabto();
--
2.17.1
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