[PATCH v3] rte_dump_stack: make in async signal safe

[Stephen Hemminger <stephen@networkplumber.org>]

rte_dump_stack needs to be usable in situations when a bug is
encountered and from signal handlers (such as SEGV).

Glibc backtrace_symbols() calls malloc which makes it
dangerous in a signal handler that is handling errors that maybe
due to memory corruption. Additionally, rte_log() is unsafe because
syslog() is not signal safe; printf() is also documented as
not being safe.

This version formats message and uses writev for each line in a manner
similar to what glibc version of backtrace_symbols_fd() does. The
FreeBSD version of backtrace_symbols_fd() is not signal safe.

Sample output:

0: ./build/app/dpdk-testpmd (rte_dump_stack+0x2b) [560a6e9c002b]
1: ./build/app/dpdk-testpmd (main+0xad) [560a6decd5ad]
2: /lib/x86_64-linux-gnu/libc.so.6 (__libc_start_main+0xcd) [7fd43d3e27fd]
3: ./build/app/dpdk-testpmd (_start+0x2a) [560a6e83628a]

Bugzilla ID: 929
Acked-by: Morten Brørup <mb@smartsharesystems.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
v3
  - merge previous two patches into one
    common Linux/FreeBSD code.
  - rewrite the code to not use functions which are not
    documented to be signal safe.

 lib/eal/freebsd/eal_debug.c |  43 -------------
 lib/eal/freebsd/meson.build |   1 -
 lib/eal/include/rte_debug.h |   2 +-
 lib/eal/linux/eal_debug.c   |  38 -----------
 lib/eal/linux/meson.build   |   1 -
 lib/eal/unix/eal_debug.c    | 123 ++++++++++++++++++++++++++++++++++++
 lib/eal/unix/meson.build    |   1 +
 7 files changed, 125 insertions(+), 84 deletions(-)
 delete mode 100644 lib/eal/freebsd/eal_debug.c
 delete mode 100644 lib/eal/linux/eal_debug.c
 create mode 100644 lib/eal/unix/eal_debug.c

diff --git a/lib/eal/freebsd/eal_debug.c b/lib/eal/freebsd/eal_debug.c
deleted file mode 100644
index 64dab4e0da24..000000000000
--- a/lib/eal/freebsd/eal_debug.c
+++ /dev/null
@@ -1,43 +0,0 @@
-/* SPDX-License-Identifier: BSD-3-Clause
- * Copyright(c) 2010-2014 Intel Corporation
- */
-
-#ifdef RTE_BACKTRACE
-#include <execinfo.h>
-#endif
-#include <stdarg.h>
-#include <signal.h>
-#include <stdlib.h>
-#include <stdio.h>
-#include <stdint.h>
-
-#include <rte_log.h>
-#include <rte_debug.h>
-#include <rte_common.h>
-#include <rte_eal.h>
-
-#define BACKTRACE_SIZE 256
-
-/* dump the stack of the calling core */
-void rte_dump_stack(void)
-{
-#ifdef RTE_BACKTRACE
-	void *func[BACKTRACE_SIZE];
-	char **symb = NULL;
-	int size;
-
-	size = backtrace(func, BACKTRACE_SIZE);
-	symb = backtrace_symbols(func, size);
-
-	if (symb == NULL)
-		return;
-
-	while (size > 0) {
-		rte_log(RTE_LOG_ERR, RTE_LOGTYPE_EAL,
-			"%d: [%s]\n", size, symb[size - 1]);
-		size --;
-	}
-
-	free(symb);
-#endif /* RTE_BACKTRACE */
-}
diff --git a/lib/eal/freebsd/meson.build b/lib/eal/freebsd/meson.build
index 398ceab71d03..85cca5a096ca 100644
--- a/lib/eal/freebsd/meson.build
+++ b/lib/eal/freebsd/meson.build
@@ -7,7 +7,6 @@ sources += files(
         'eal.c',
         'eal_alarm.c',
         'eal_cpuflags.c',
-        'eal_debug.c',
         'eal_dev.c',
         'eal_hugepage_info.c',
         'eal_interrupts.c',
diff --git a/lib/eal/include/rte_debug.h b/lib/eal/include/rte_debug.h
index c4bc71ce28f5..2c4b94a7c9bf 100644
--- a/lib/eal/include/rte_debug.h
+++ b/lib/eal/include/rte_debug.h
@@ -22,7 +22,7 @@ extern "C" {
 #endif
 
 /**
- * Dump the stack of the calling core to the console.
+ * Dump the stack of the calling core to the standard error.
  */
 void rte_dump_stack(void);
 
diff --git a/lib/eal/linux/eal_debug.c b/lib/eal/linux/eal_debug.c
deleted file mode 100644
index b0ecf5a9dcde..000000000000
--- a/lib/eal/linux/eal_debug.c
+++ /dev/null
@@ -1,38 +0,0 @@
-/* SPDX-License-Identifier: BSD-3-Clause
- * Copyright(c) 2010-2014 Intel Corporation
- */
-
-#ifdef RTE_BACKTRACE
-#include <execinfo.h>
-#endif
-#include <stdlib.h>
-#include <stdio.h>
-
-#include <rte_log.h>
-#include <rte_debug.h>
-
-#define BACKTRACE_SIZE 256
-
-/* dump the stack of the calling core */
-void rte_dump_stack(void)
-{
-#ifdef RTE_BACKTRACE
-	void *func[BACKTRACE_SIZE];
-	char **symb = NULL;
-	int size;
-
-	size = backtrace(func, BACKTRACE_SIZE);
-	symb = backtrace_symbols(func, size);
-
-	if (symb == NULL)
-		return;
-
-	while (size > 0) {
-		rte_log(RTE_LOG_ERR, RTE_LOGTYPE_EAL,
-			"%d: [%s]\n", size, symb[size - 1]);
-		size --;
-	}
-
-	free(symb);
-#endif /* RTE_BACKTRACE */
-}
diff --git a/lib/eal/linux/meson.build b/lib/eal/linux/meson.build
index 65f2ac6b4798..3cccfa36c0a4 100644
--- a/lib/eal/linux/meson.build
+++ b/lib/eal/linux/meson.build
@@ -7,7 +7,6 @@ sources += files(
         'eal.c',
         'eal_alarm.c',
         'eal_cpuflags.c',
-        'eal_debug.c',
         'eal_dev.c',
         'eal_hugepage_info.c',
         'eal_interrupts.c',
diff --git a/lib/eal/unix/eal_debug.c b/lib/eal/unix/eal_debug.c
new file mode 100644
index 000000000000..79b6f2fea2b9
--- /dev/null
+++ b/lib/eal/unix/eal_debug.c
@@ -0,0 +1,123 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2010-2014 Intel Corporation
+ */
+
+#include <rte_debug.h>
+
+
+#ifdef RTE_BACKTRACE
+
+#include <dlfcn.h>
+#include <execinfo.h>
+#include <string.h>
+#include <sys/uio.h>
+#include <unistd.h>
+
+#define BACKTRACE_SIZE 256
+
+/*
+ * Convert number to string and return start of string.
+ * Note: string does not start at beginning of buffer.
+ */
+static char *safe_itoa(long val, char *buf, size_t len, unsigned int radix)
+{
+	char *bp = buf + len;
+	static const char hexdigit[] = "0123456789abcdef";
+
+	*--bp = '\0'; /* Null terminate the string */
+	do {
+		/* if buffer is not big enough, then truncate */
+		if (bp == buf)
+			return bp;
+
+		*--bp = hexdigit[val % radix];
+		val /= radix;
+	} while (val != 0);
+
+	return bp;
+}
+
+
+/* Dump the stack of the calling core
+ *
+ * To be safe in signal handler requires limiting what functions are
+ * used in this code since may be called from inside libc or
+ * when malloc poll is corrupt.
+ *
+ * Most of libc is therefore not safe, include RTE_LOG (calls syslog);
+ * backtrace_symbols (calls malloc), etc.
+ */
+void rte_dump_stack(void)
+{
+	void *func[BACKTRACE_SIZE];
+	Dl_info info;
+	char buf1[8], buf2[32], buf3[32], buf4[32];
+	struct iovec iov[10];
+	int i, size;
+
+	size = backtrace(func, BACKTRACE_SIZE);
+
+	for (i = 0; i < size; i++) {
+		struct iovec *io = iov;
+		char *str;
+		uintptr_t base;
+		long offset;
+		void *pc = func[i];
+
+/* Macro to put string onto set of iovecs
+ * cast is to suppress warnings about lose of const qualifier
+ */
+#define PUSH_IOV(io, str) {					\
+		(io)->iov_base = (char *)(uintptr_t)str;	\
+		(io)->iov_len = strlen(str);			\
+		++io; }
+
+		/* output stack frame number */
+		str = safe_itoa(i, buf1, sizeof(buf1), 10);
+		PUSH_IOV(io, str);	/* iov[0] */
+		PUSH_IOV(io, ": ");	/* iov[1] */
+
+		/* Lookup the symbol information */
+		if (dladdr (pc, &info) == 0) {
+			PUSH_IOV(io, "?? [");
+		} else {
+			const char *fname;
+
+			if (info.dli_fname && *info.dli_fname)
+				fname = info.dli_fname;
+			else
+				fname = "(vdso)";
+			PUSH_IOV(io, fname);	/* iov[2] */
+			PUSH_IOV(io, " (");	/* iov[3] */
+
+			if (info.dli_saddr != NULL) {
+				PUSH_IOV(io, info.dli_sname);	/* iov[4] */
+				base = (uintptr_t)info.dli_saddr;
+			} else {
+				str = safe_itoa((unsigned long)info.dli_fbase,
+						buf3, sizeof(buf3), 16);
+				PUSH_IOV(io, str);
+				base = (uintptr_t)info.dli_fbase;
+			}
+
+			PUSH_IOV(io, "+0x");	/* iov[5] */
+
+			offset = (uintptr_t)pc - base;
+			str = safe_itoa(offset, buf4, sizeof(buf4), 16);
+			PUSH_IOV(io, str);	/* iov[6] */
+
+			PUSH_IOV(io, ") [");	/* iov[7] */
+		}
+
+		str = safe_itoa((unsigned long)pc, buf2, sizeof(buf2), 16);
+		PUSH_IOV(io, str);	/* iov[8] */
+		PUSH_IOV(io, "]\n");	/* iov[9] */
+
+		if (writev(STDERR_FILENO, iov, io - iov) < 0)
+			break;
+	}
+}
+#else
+/* stub if not enabled */
+void rte_dump_stack(void) { }
+#endif /* RTE_BACKTRACE */
diff --git a/lib/eal/unix/meson.build b/lib/eal/unix/meson.build
index a22ea7cabc46..9c59f3d31693 100644
--- a/lib/eal/unix/meson.build
+++ b/lib/eal/unix/meson.build
@@ -2,6 +2,7 @@
 # Copyright(c) 2020 Dmitry Kozlyuk
 
 sources += files(
+        'eal_debug.c',
         'eal_file.c',
         'eal_unix_memory.c',
         'eal_unix_timer.c',
-- 
2.35.1