dtrace: handle .init.scratch section in /proc/kallmodsyms

The introduction of the .init.scratch section in Linux 5.2-rc6 via e1bfa87
("x86/mm: Create a workarea in the kernel for SME early encryption") led to
the consistent failure of
- test/unittest/aggs/tst.aggmod_full2.sh
- test/unittest/consumer/tst.merge_ranges_bug25767469.c
- test/unittest/consumer/tst.symbols.c
This init section, related to the kernel, appears in /proc/kall[mod]syms
after the end of kernel addresses, causing problems for DTrace's ways of
reading /proc/kallmodsyms.

Until the kernel is fixed not to write this init section to
/proc/kall[mod]syms, add fixes to DTrace userspace code wherever, including
in tests, it reads /proc/kallmodsyms.

[Orabug: 30149066]
Signed-off-by: Eugene Loh <eugene.loh@oracle.com>
Reviewed-by: Nick Alcock <nick.alcock@oracle.com>

libdtrace/dt_module.c

@@ -1056,6 +1056,27 @@ dt_kern_module_find_ctf(dtrace_hdl_t *dtp, dt_module_t *dmp)
 	}
 }
 
+/*
+ * We will use kernel_flag to track which symbols we are reading.
+ *
+ * /proc/kallmodsyms starts with kernel (and built-in-module) symbols.
+ *
+ * The last kernel address is expected to have the name "_end",
+ * but there might also be a symbol "__brk_limit" with that address.
+ * Set the KERNEL_FLAG_KERNEL_END flag while these addresses are read.
+ *
+ * Otherwise, symbols in /proc/kallmodsyms will normally belong to
+ * loadable modules.  Set the KERNEL_FLAG_LOADABLE flag once these
+ * symbols are reached.
+ *
+ * Another odd case is the .init.scratch section introduced by e1bfa87
+ * ("x86/mm: Create a workarea in the kernel for SME early encryption"),
+ * which appears in 5.2-rc6.  We ignore this section by setting the
+ * KERNEL_FLAG_INIT_SCRATCH flag.
+ */
+#define KERNEL_FLAG_KERNEL_END 1
+#define KERNEL_FLAG_LOADABLE 2
+#define KERNEL_FLAG_INIT_SCRATCH 4
 /*
  * Update our module cache.  For each line in /proc/kallmodsyms, create or
  * populate the dt_module_t for this module (if necessary), extend its address
@@ -1069,7 +1090,7 @@ dt_kern_module_find_ctf(dtrace_hdl_t *dtp, dt_module_t *dmp)
 static int
 dt_modsym_update(dtrace_hdl_t *dtp, const char *line)
 {
-	static int kernel_flag = 1;
+	static uint_t kernel_flag = 0;
 	static dt_module_t *last_dmp = NULL;
 	static int last_sym_text = -1;
 
@@ -1110,23 +1131,23 @@ dt_modsym_update(dtrace_hdl_t *dtp, const char *line)
 		return 0;
 
 	/*
-	 * /proc/kallmodsyms starts with kernel (and built-in-module) symbols.
-	 * The last kernel address is expected to have the name "_end".
-	 * (There might also be a symbol "__brk_limit" with that address.)
-	 * Thereafter, symbols in /proc/kallmodsyms will belong to loadable
-	 * modules.
-	 *
-	 * kernel_flag==+1 means normal kernel (and built-in-module) symbols
-	 * kernel_flag==-1 means loadable-module symbols
-	 * kernel_flag==0 is an odd in-between case for the section markers
-	 *   (they signal the imminent end of the kernel section)
+	 * Skip over the .init.scratch section.
 	 */
+	if (strcmp(sym_name, "__init_scratch_begin") == 0) {
+		kernel_flag |= KERNEL_FLAG_INIT_SCRATCH;
+		return 0;
+	} else if (strcmp(sym_name, "__init_scratch_end") == 0) {
+		kernel_flag &= ~ KERNEL_FLAG_INIT_SCRATCH;
+		return 0;
+	} else if (kernel_flag & KERNEL_FLAG_INIT_SCRATCH) {
+		return 0;
+	}
 
 	if ((strcmp(sym_name, "_end") == 0) ||
 	    (strcmp(sym_name, "__brk_limit") == 0))
-		kernel_flag = 0;
-	else if (kernel_flag == 0)
-		kernel_flag = -1;
+		kernel_flag |= KERNEL_FLAG_KERNEL_END;
+	else if (kernel_flag & KERNEL_FLAG_KERNEL_END)
+		kernel_flag = KERNEL_FLAG_LOADABLE;
 
 	/*
 	 * Special case: rename the 'ctf' module to 'shared_ctf': the
@@ -1208,7 +1229,7 @@ dt_modsym_update(dtrace_hdl_t *dtp, const char *line)
 	if (sym_size == 0)
 		return 0;
 
-	if (kernel_flag >= 0) {
+	if ((kernel_flag & KERNEL_FLAG_LOADABLE) == 0) {
 		/*
 		 * The kernel and built-in modules are in address order
 		 * in /proc/kallmodsyms.

test/unittest/aggs/tst.aggmod_full2.sh

@@ -53,6 +53,8 @@ int main(int argc, char **argv) {
 	char *line = NULL;
 	size_t line_n = 0;
 	FILE *fd;
+	unsigned int kernel_flag = 0;
+
 	if ((fd = fopen("/proc/kallmodsyms", "r")) == NULL) return 1;
 	while ((getline(&line, &line_n, fd)) > 0) {
 		long long unsigned addr, size;
@@ -72,6 +74,17 @@ int main(int argc, char **argv) {
 		/* see dt_module.c dt_modsym_update() */
 		if (type == 'a' || type == 'A')
 			continue;
+#define KERNEL_FLAG_INIT_SCRATCH 4
+		if (strcmp(symname, "__init_scratch_begin") == 0) {
+			kernel_flag |= KERNEL_FLAG_INIT_SCRATCH;
+			continue;
+		} else if (strcmp(symname, "__init_scratch_end") == 0) {
+			kernel_flag &= ~ KERNEL_FLAG_INIT_SCRATCH;
+			continue;
+		} else if (kernel_flag & KERNEL_FLAG_INIT_SCRATCH) {
+			continue;
+		}
+#undef KERNEL_FLAG_INIT_SCRATCH
 
 		/* zero-size symbol might mark the end of a range */
 		if (size == 0)

test/unittest/consumer/tst.merge_ranges_bug25767469.c

@@ -59,7 +59,7 @@ int nerrors = 0;
  */
 
 void check_module_ranges
-(size_t n, dtrace_addr_range_t *addrs, char *name, char type)
+(size_t n, dtrace_addr_range_t *addrs, const char *name, char type)
 {
 	int i;
 	/*

test/unittest/consumer/tst.symbols.c

@@ -53,6 +53,7 @@ int read_symbols() {
 	size_t line_n = 0;
 	FILE *fd;
 	int n_skip = 0, n_absolute = 0;
+	unsigned int kernel_flag = 0;
 
 	printf("read_symbols():\n");
 	if ((fd = fopen("/proc/kallmodsyms", "r")) == NULL) return 1;
@@ -90,11 +91,22 @@ int read_symbols() {
 		}
 
 		/*
-		 * Skip absolute symbols.  See dt_module.c, dt_modsym_update().
+		 * See dt_module.c, dt_modsym_update().
 		 */
 		if (symbols[nsymbols].type == 'a' ||
 		    symbols[nsymbols].type == 'A')
 			continue;
+#define KERNEL_FLAG_INIT_SCRATCH 4
+		if (strcmp(symname, "__init_scratch_begin") == 0) {
+			kernel_flag |= KERNEL_FLAG_INIT_SCRATCH;
+			continue;
+		} else if (strcmp(symname, "__init_scratch_end") == 0) {
+			kernel_flag &= ~ KERNEL_FLAG_INIT_SCRATCH;
+			continue;
+		} else if (kernel_flag & KERNEL_FLAG_INIT_SCRATCH) {
+			continue;
+		}
+#undef KERNEL_FLAG_INIT_SCRATCH
 
 		/*
 		 * In libdtrace/dt_module.c function dt_modsym_update(),