[DTrace-devel] [PATCH] No uprobes on ARM autiasp instructions

[eugene.loh at oracle.com]

From: Eugene Loh <eugene.loh at oracle.com>

New compilers emit autiasp instructions much more liberally.
A test like test/unittest/pid/tst.entry_off0.sh, which tries
to put a probe on each instruction, may fail.

Signed-off-by: Eugene Loh <eugene.loh at oracle.com>
---
 libdtrace/dt_pid.c | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/libdtrace/dt_pid.c b/libdtrace/dt_pid.c
index e2d4e540d..833e9b647 100644
--- a/libdtrace/dt_pid.c
+++ b/libdtrace/dt_pid.c
@@ -279,12 +279,17 @@ dt_pid_per_sym(dt_pid_probe_t *pp, const GElf_Sym *symp, const char *func)
 
 		nmatches++;
 	} else if (glob) {
-#if defined(__amd64)
 		/*
-		 * We need to step through the instructions to find their
-		 * offsets.  This is difficult on x86, which has variable
-		 * instruction lengths.  We invoke the disassembler in
-		 * libopcodes.
+		 * We need the instructions for two reasons:
+		 * = On x86, instructions have varying lengths.  So,
+		 *   to step through the instructions, we need to
+		 *   disassemble them to know what they are.
+		 *   We invoke the disassembler in libopcodes.
+		 *   (On ARM, we step through 4 bytes at a time.)
+		 * = On both x86 and arm, we want to skip certain
+		 *   instructions.  So, again, we need to know what they are.
+		 */
+		/*
 		 *
 		 * We look for the Elf pointer.  It is already stored in
 		 * file_elf in file_info_t, but getting it back over here
@@ -298,7 +303,6 @@ dt_pid_per_sym(dt_pid_probe_t *pp, const GElf_Sym *symp, const char *func)
 		GElf_Shdr shdr;
 		Elf_Data *data;
 		size_t shstrndx, off;
-		disassembler_ftype disasm;
 
 		/* Set things up. */
 		fd = open(pp->dpp_fname, O_RDONLY);
@@ -344,12 +348,14 @@ dt_pid_per_sym(dt_pid_probe_t *pp, const GElf_Sym *symp, const char *func)
 		/* Get the instructions. */
 		data = elf_getdata(scn, NULL);
 
+#if defined(__amd64)
 		/*
 		 * "Disassemble" instructions just to get the offsets.
 		 *
 		 * Unfortunately, libopcodes's disassembler() has a different
 		 * interface in binutils versions before 2.29.
 		 */
+		disassembler_ftype disasm;
 #if defined(HAVE_DIS1) == defined(HAVE_DIS4)
 #error expect disassembler() to have 1 or else 4 arguments
 #endif
@@ -390,6 +396,11 @@ dt_pid_per_sym(dt_pid_probe_t *pp, const GElf_Sym *symp, const char *func)
 			/* Newer kernels do not allow uprobes on "hlt" instructions. */
 			if ((unsigned int)disasm_info.buffer[off] == 0xf4)
 				continue;
+#else
+			/* On ARM, we cannot place uprobes on "autiasp" instructions. */
+			if (*((unsigned int *)(data->d_buf + (sym.st_value + off - shdr.sh_addr)))
+			    == 0xd50323bf)
+				continue;
 #endif
 
 			snprintf(offstr, sizeof(offstr), "%lx", off);
-- 
2.43.5