Implement decoding of signal masks associated with signalfd file descriptors

When signalfds are used, normal signal handling method is usually
disabled, leaving strace without signals to catch and decode.

This patch adds decoding of signal masks associated with signalfd file
descriptors.

Decoding the signalfd_siginfo struct requires additional work mentioned
in github#199.

Signed-off-by: leedagee <leedageea@gmail.com>

* NEWS: Mention this change.
* doc/strace.1.in: Document --decode-fds=signalfd.
* src/strace.c (usage): Likewise.
* src/number_set.h (enum decode_fd_bits): Add DECODE_FD_SIGNALFD.
* src/filter_qualify.c (decode_fd_str_to_uint): Handle signalfd.
* src/util.c (print_fdinfo_sigmask, printsignalfd): New functions.
(printfd_pid_with_finfo): Use printsignalfd when DECODE_FD_SIGNALFD
is set in decode_fd_set.
* tests/signalfd4.c [PRINT_SIGNALFD]: Check decoding of signal masks
associated with signalfd file descriptors.
* tests/signalfd4-yy.c: New file.
* tests/pure_executables.list: Add signalfd4-yy.
* tests/.gitignore: Likewise.
* tests/gen_tests.in (signalfd4): Add -a32.
(signalfd4-yy): New test.

Co-authored-by: Dmitry V. Levin <ldv@strace.io>

5 files changed, 39 insertions, 5 deletions

diff --git a/tests/.gitignore b/tests/.gitignore
index 4c753e324..d0f99f01e 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -982,6 +982,7 @@ signal
 signal_receive
 signal_receive--pidns-translation
 signalfd4
+signalfd4-yy
 sigpending
 sigprocmask
 sigreturn
diff --git a/tests/gen_tests.in b/tests/gen_tests.in
index 1316ad6e8..f19963b06 100644
--- a/tests/gen_tests.in
+++ b/tests/gen_tests.in
@@ -960,7 +960,8 @@ siginfo	-e trace=none
 signal	-a25 -e signal=none -e trace='/^signal$'
 signal_receive	-a16 -e trace=kill
 signal_receive--pidns-translation	test_pidns -a16 -e trace=kill
-signalfd4
+signalfd4	-a32
+signalfd4-yy	--trace=signalfd4 -yy
 sigpending	-a15
 sigprocmask	-a34
 sigreturn	-esignal='!USR1'
diff --git a/tests/pure_executables.list b/tests/pure_executables.list
index a1315f64e..4c32d8b99 100755
--- a/tests/pure_executables.list
+++ b/tests/pure_executables.list
@@ -695,6 +695,7 @@ sigaltstack
 siginfo
 signal
 signalfd4
+signalfd4-yy
 sigpending
 sigprocmask
 sigreturn
diff --git a/tests/signalfd4-yy.c b/tests/signalfd4-yy.c
new file mode 100644
index 000000000..6a5262628
--- /dev/null
+++ b/tests/signalfd4-yy.c
@@ -0,0 +1,4 @@
+#define SKIP_IF_PROC_IS_UNAVAILABLE skip_if_unavailable("/proc/self/fd/")
+#define PRINT_SIGNALFD
+
+#include "signalfd4.c"
diff --git a/tests/signalfd4.c b/tests/signalfd4.c
index e45e9425c..97e7977a2 100644
--- a/tests/signalfd4.c
+++ b/tests/signalfd4.c
@@ -20,20 +20,47 @@
 # include <sys/signalfd.h>
 # include "kernel_fcntl.h"
 
+#ifndef SKIP_IF_PROC_IS_UNAVAILABLE
+# define SKIP_IF_PROC_IS_UNAVAILABLE
+#endif
+
 int
 main(void)
 {
-	const char *const sigs = SIGUSR2 < SIGCHLD ? "USR2 CHLD" : "CHLD USR2";
+	SKIP_IF_PROC_IS_UNAVAILABLE;
+
+	const char *const sigs1 = "USR2";
+	const char *const sigs2 = SIGUSR2 < SIGCHLD ? "USR2 CHLD" : "CHLD USR2";
 	const unsigned int size = get_sigset_size();
 
 	sigset_t mask;
 	sigemptyset(&mask);
 	sigaddset(&mask, SIGUSR2);
+
+	int fd = signalfd(-1, &mask, SFD_CLOEXEC | SFD_NONBLOCK);
+
+#ifdef PRINT_SIGNALFD
+	if (fd == -1)
+		perror_msg_and_skip("signalfd");
+#endif
+
+	printf("signalfd4(-1, [%s], %u, SFD_CLOEXEC|SFD_NONBLOCK) = %s",
+	       sigs1, size, sprintrc(fd));
+#ifdef PRINT_SIGNALFD
+	printf("<signalfd:[%s]>\n", sigs1);
+#else
+	putchar('\n');
+#endif
+
 	sigaddset(&mask, SIGCHLD);
+	fd = signalfd(fd, &mask, 0);
 
-	int fd = signalfd(-1, &mask, O_CLOEXEC | O_NONBLOCK);
-	printf("signalfd4(-1, [%s], %u, SFD_CLOEXEC|SFD_NONBLOCK) = %s\n",
-	       sigs, size, sprintrc(fd));
+#ifdef PRINT_SIGNALFD
+	printf("signalfd4(%d<signalfd:[%s]>, [%s], %u, 0) = %s<signalfd:[%s]>\n",
+	       fd, sigs1, sigs2, size, sprintrc(fd), sigs2);
+#else
+	printf("signalfd4(%d, [%s], %u, 0) = %s\n", fd, sigs2, size, sprintrc(fd));
+#endif
 
 	puts("+++ exited with 0 +++");
 	return 0;