From 7f0ae84c80aae6fe8f7573343fe1ab455d18b5d8 Mon Sep 17 00:00:00 2001 From: George Barrett Date: Sat, 11 Jan 2020 06:30:28 +1100 Subject: [PATCH] Fix handling of null stap semaphores 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 * 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 * 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. --- gdb/ChangeLog | 7 +++++ gdb/stap-probe.c | 7 ++--- gdb/testsuite/ChangeLog | 11 ++++++++ gdb/testsuite/gdb.base/stap-probe.c | 2 ++ gdb/testsuite/gdb.base/stap-probe.exp | 38 ++++++++++++++++++++++----- 5 files changed, 55 insertions(+), 10 deletions(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 425bafa9b26..0e5c8a95275 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,10 @@ +2020-01-10 George Barrett + + * 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 * tui/tui-source.c (tui_source_window::do_scroll_vertical): Update diff --git a/gdb/stap-probe.c b/gdb/stap-probe.c index 5e9a043ffeb..50f6d518133 100644 --- a/gdb/stap-probe.c +++ b/gdb/stap-probe.c @@ -1430,9 +1430,6 @@ stap_modify_semaphore (CORE_ADDR address, int set, struct gdbarch *gdbarch) 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) { @@ -1466,6 +1463,8 @@ stap_modify_semaphore (CORE_ADDR address, int set, 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); } @@ -1474,6 +1473,8 @@ stap_probe::set_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); } diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog index 84fa9aec6db..29d6af2008d 100644 --- a/gdb/testsuite/ChangeLog +++ b/gdb/testsuite/ChangeLog @@ -1,3 +1,14 @@ +2020-01-10 George Barrett + + * 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 * gdb.base/stap-probe.c: Rename USE_PROBES to USE_SEMAPHORES. diff --git a/gdb/testsuite/gdb.base/stap-probe.c b/gdb/testsuite/gdb.base/stap-probe.c index 3d742d1253e..5cb549498a5 100644 --- a/gdb/testsuite/gdb.base/stap-probe.c +++ b/gdb/testsuite/gdb.base/stap-probe.c @@ -31,6 +31,8 @@ __extension__ unsigned short test_pstr_semaphore __attribute__ ((unused)) __attr __extension__ unsigned short test_ps_semaphore __attribute__ ((unused)) __attribute__ ((section (".probes"))); #else +int relocation_marker __attribute__ ((unused)); + #define TEST 1 #define TEST2 1 diff --git a/gdb/testsuite/gdb.base/stap-probe.exp b/gdb/testsuite/gdb.base/stap-probe.exp index fce52864510..398bc8936cc 100644 --- a/gdb/testsuite/gdb.base/stap-probe.exp +++ b/gdb/testsuite/gdb.base/stap-probe.exp @@ -18,14 +18,20 @@ standard_testfile # 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} $srcfile \ - [concat additional_flags=$arg debug]]} { + [concat $args debug]]} { return -1 } + 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 } @@ -33,7 +39,7 @@ proc stap_test {exec_name {arg ""}} { 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 { @@ -47,6 +53,20 @@ proc stap_test {exec_name {arg ""}} { 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" @@ -97,11 +117,11 @@ proc stap_test {exec_name {arg ""}} { return 0 } -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} ${testfile}.c \ - [concat additional_flags=$arg nodebug optimize=-O2]]} { + [concat $args nodebug optimize=-O2]]} { return -1 } @@ -168,10 +188,14 @@ with_test_prefix "without semaphore, not optimized" { untested "stap probe test failed" return -1 } + + foreach_with_prefix pie { "nopie" "pie" } { + stap_test "stap-probe-nosem-noopt-$pie" $pie + } } with_test_prefix "with semaphore, not optimized" { - stap_test "stap-probe-sem-noopt" "-DUSE_SEMAPHORES" + stap_test "stap-probe-sem-noopt" additional_flags=-DUSE_SEMAPHORES } with_test_prefix "without semaphore, optimized" { @@ -179,5 +203,5 @@ with_test_prefix "without 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 } -- 2.30.2