According to the SystemTap documentation on user-space probes[0], stap
probe points without semaphores are denoted by setting the semaphore
address in the probe's note to zero. At present the code does do a
comparison of the semaphore address against zero, but only after it's
been relocated; as such it will (almost?) always fail, commonly
resulting in GDB trying to overwrite the ELF magic located at the
image's base address.
This commit tests the address as specified in the SDT note rather than
the relocated value in order to correctly detect absent probe
semaphores.
[0]: https://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation
gdb/Changelog:
2020-01-11 George Barrett <bob@bob131.so>
* stap-probe.c (stap_modify_semaphore): Don't check for null
semaphores.
(stap_probe::set_semaphore, stap_probe::clear_semaphore): Check
for null semaphores.
gdb/testsuite/ChangeLog:
2020-01-11 George Barrett <bob@bob131.so>
* gdb.base/stap-probe.c (relocation_marker): Add dummy variable
to help in finding the image relocation offset.
* gdb.base/stap-probe.exp (stap_test): Accept arbitrary compile
options in arguments.
(stap_test_no_debuginfo): Likewise.
(stap-probe-nosem-noopt-pie, stap-probe-nosem-noopt-nopie): Add
test variants.
(stap_test): Add null semaphore relocation test.
+2020-01-10 George Barrett <bob@bob131.so>
+
+ * stap-probe.c (stap_modify_semaphore): Don't check for null
+ semaphores.
+ (stap_probe::set_semaphore, stap_probe::clear_semaphore): Check
+ for null semaphores.
+
2020-01-09 Andrew Burgess <andrew.burgess@embecosm.com>
* tui/tui-source.c (tui_source_window::do_scroll_vertical): Update
2020-01-09 Andrew Burgess <andrew.burgess@embecosm.com>
* tui/tui-source.c (tui_source_window::do_scroll_vertical): Update
struct type *type = builtin_type (gdbarch)->builtin_unsigned_short;
ULONGEST value;
struct type *type = builtin_type (gdbarch)->builtin_unsigned_short;
ULONGEST value;
- if (address == 0)
- return;
-
/* Swallow errors. */
if (target_read_memory (address, bytes, TYPE_LENGTH (type)) != 0)
{
/* Swallow errors. */
if (target_read_memory (address, bytes, TYPE_LENGTH (type)) != 0)
{
void
stap_probe::set_semaphore (struct objfile *objfile, struct gdbarch *gdbarch)
{
void
stap_probe::set_semaphore (struct objfile *objfile, struct gdbarch *gdbarch)
{
+ if (m_sem_addr == 0)
+ return;
stap_modify_semaphore (relocate_address (m_sem_addr, objfile), 1, gdbarch);
}
stap_modify_semaphore (relocate_address (m_sem_addr, objfile), 1, gdbarch);
}
void
stap_probe::clear_semaphore (struct objfile *objfile, struct gdbarch *gdbarch)
{
void
stap_probe::clear_semaphore (struct objfile *objfile, struct gdbarch *gdbarch)
{
+ if (m_sem_addr == 0)
+ return;
stap_modify_semaphore (relocate_address (m_sem_addr, objfile), 0, gdbarch);
}
stap_modify_semaphore (relocate_address (m_sem_addr, objfile), 0, gdbarch);
}
+2020-01-10 George Barrett <bob@bob131.so>
+
+ * gdb.base/stap-probe.c (relocation_marker): Add dummy variable
+ to help in finding the image relocation offset.
+ * gdb.base/stap-probe.exp (stap_test): Accept arbitrary compile
+ options in arguments.
+ (stap_test_no_debuginfo): Likewise.
+ (stap-probe-nosem-noopt-pie, stap-probe-nosem-noopt-nopie): Add
+ test variants.
+ (stap_test): Add null semaphore relocation test.
+
2020-01-10 George Barrett <bob@bob131.so>
* gdb.base/stap-probe.c: Rename USE_PROBES to USE_SEMAPHORES.
2020-01-10 George Barrett <bob@bob131.so>
* gdb.base/stap-probe.c: Rename USE_PROBES to USE_SEMAPHORES.
__extension__ unsigned short test_ps_semaphore __attribute__ ((unused)) __attribute__ ((section (".probes")));
#else
__extension__ unsigned short test_ps_semaphore __attribute__ ((unused)) __attribute__ ((section (".probes")));
#else
+int relocation_marker __attribute__ ((unused));
+
#define TEST 1
#define TEST2 1
#define TEST 1
#define TEST2 1
# Run the tests. We run the tests two different ways: once with a
# plain probe, and once with a probe that has an associated semaphore.
# This returns -1 on failure to compile or start, 0 otherwise.
# Run the tests. We run the tests two different ways: once with a
# plain probe, and once with a probe that has an associated semaphore.
# This returns -1 on failure to compile or start, 0 otherwise.
-proc stap_test {exec_name {arg ""}} {
+proc stap_test {exec_name {args ""}} {
global testfile hex srcfile
if {[prepare_for_testing "failed to prepare" ${exec_name} $srcfile \
global testfile hex srcfile
if {[prepare_for_testing "failed to prepare" ${exec_name} $srcfile \
- [concat additional_flags=$arg debug]]} {
+ [concat $args debug]]} {
+ set semaphore_addr_var ""
+ if {[string first "-DUSE_SEMAPHORES" $args] == -1} {
+ gdb_test_no_output "set breakpoint always-inserted on"
+ set semaphore_addr_var [get_hexadecimal_valueof "&relocation_marker" "0"]
+ }
+
if ![runto_main] {
return -1
}
if ![runto_main] {
return -1
}
gdb_test "print \$_probe_argc" "No probe at PC $hex" \
"check argument not at probe point"
gdb_test "print \$_probe_argc" "No probe at PC $hex" \
"check argument not at probe point"
- if {[string first "-DUSE_SEMAPHORES" $arg] != -1} {
+ if {[string first "-DUSE_SEMAPHORES" $args] != -1} {
gdb_test "info probes stap" \
"test *user *$hex *$hex .*"
} else {
gdb_test "info probes stap" \
"test *user *$hex *$hex .*"
} else {
fail "run to -pstap test:user"
}
fail "run to -pstap test:user"
}
+ if {[string first "-DUSE_SEMAPHORES" $args] == -1} {
+ set relocation_base \
+ [expr [get_hexadecimal_valueof "&relocation_marker" "0"] - $semaphore_addr_var]
+ if {$relocation_base != 0} {
+ # Checks that GDB doesn't mistakenly relocate and write to null
+ # semaphore addresses. If it were to relocate a zero-valued
+ # semaphore address and increment the value at that address, we
+ # would expect to see "\200ELF" here instead.
+ gdb_test "p (*(char*) $relocation_base)@4" \
+ " = \"\\\\177ELF\"" \
+ "null semaphore relocation"
+ }
+ }
+
# Test probe arguments.
gdb_test "print \$_probe_argc" " = 1" \
"print \$_probe_argc for probe user"
# Test probe arguments.
gdb_test "print \$_probe_argc" " = 1" \
"print \$_probe_argc for probe user"
-proc stap_test_no_debuginfo {exec_name {arg ""}} {
+proc stap_test_no_debuginfo {exec_name {args ""}} {
global testfile hex
if {[prepare_for_testing "failed to prepare" ${exec_name} ${testfile}.c \
global testfile hex
if {[prepare_for_testing "failed to prepare" ${exec_name} ${testfile}.c \
- [concat additional_flags=$arg nodebug optimize=-O2]]} {
+ [concat $args nodebug optimize=-O2]]} {
untested "stap probe test failed"
return -1
}
untested "stap probe test failed"
return -1
}
+
+ foreach_with_prefix pie { "nopie" "pie" } {
+ stap_test "stap-probe-nosem-noopt-$pie" $pie
+ }
}
with_test_prefix "with semaphore, not optimized" {
}
with_test_prefix "with semaphore, not optimized" {
- stap_test "stap-probe-sem-noopt" "-DUSE_SEMAPHORES"
+ stap_test "stap-probe-sem-noopt" additional_flags=-DUSE_SEMAPHORES
}
with_test_prefix "without semaphore, optimized" {
}
with_test_prefix "without semaphore, optimized" {
}
with_test_prefix "with semaphore, optimized" {
}
with_test_prefix "with semaphore, optimized" {
- stap_test_no_debuginfo "stap-probe-sem-opt" "-DUSE_SEMAPHORES"
+ stap_test_no_debuginfo "stap-probe-sem-opt" additional_flags=-DUSE_SEMAPHORES