From 19007d955670a183fdf79408301d403b43eb7db1 Mon Sep 17 00:00:00 2001 From: Luis Machado Date: Thu, 10 Dec 2020 16:51:20 -0300 Subject: [PATCH] Fix TBI handling for watchpoints When inserting hw watchpoints, we take care of masking off the top byte of the address (and sign-extending it if needed). This guarantees we won't pass tagged addresses to the kernel via ptrace. However, from the kernel documentation on tagged pointers... "Non-zero tags are not preserved when delivering signals. This means that signal handlers in applications making use of tags cannot rely on the tag information for user virtual addresses being maintained for fields inside siginfo_t. One exception to this rule is for signals raised in response to watchpoint debug exceptions, where the tag information will be preserved." So the stopped data address after a hw watchpoint hit can be potentially tagged, and we don't handle this in GDB at the moment. This results in GDB missing a hw watchpoint hit and attempting to step over an unsteppable hw watchpoint, causing it to spin endlessly. The following patch fixes this by adjusting the stopped data address and adds some tests to expose the problem. gdb/ChangeLog: 2020-12-16 Luis Machado * aarch64-linux-nat.c (aarch64_linux_nat_target::stopped_data_address): Handle the TBI. gdbserver/ChangeLog: 2020-12-16 Luis Machado * linux-aarch64-low.cc (address_significant): New function. (aarch64_target::low_stopped_data_address): Handle the TBI. gdb/testsuite/ChangeLog: 2020-12-16 Luis Machado * gdb.arch/aarch64-tagged-pointer.c (main): Add a few more pointer-based memory accesses. * gdb.arch/aarch64-tagged-pointer.exp: Exercise additional hw watchpoint cases. --- gdb/ChangeLog | 5 ++++ gdb/aarch64-linux-nat.c | 8 +++++- gdb/testsuite/ChangeLog | 7 +++++ .../gdb.arch/aarch64-tagged-pointer.c | 8 +++++- .../gdb.arch/aarch64-tagged-pointer.exp | 27 ++++++++++++------- gdbserver/ChangeLog | 5 ++++ gdbserver/linux-aarch64-low.cc | 24 ++++++++++++++++- 7 files changed, 71 insertions(+), 13 deletions(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 979d26eee2..764329d52f 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,8 @@ +2020-12-16 Luis Machado + + * aarch64-linux-nat.c + (aarch64_linux_nat_target::stopped_data_address): Handle the TBI. + 2020-12-15 Rae Kim * cli/cli-script.c (do_document_command): Rename from diff --git a/gdb/aarch64-linux-nat.c b/gdb/aarch64-linux-nat.c index 77d5863a56..b3bbde4b92 100644 --- a/gdb/aarch64-linux-nat.c +++ b/gdb/aarch64-linux-nat.c @@ -877,6 +877,13 @@ aarch64_linux_nat_target::stopped_data_address (CORE_ADDR *addr_p) || (siginfo.si_code & 0xffff) != TRAP_HWBKPT) return false; + /* Make sure to ignore the top byte, otherwise we may not recognize a + hardware watchpoint hit. The stopped data addresses coming from the + kernel can potentially be tagged addresses. */ + struct gdbarch *gdbarch = thread_architecture (inferior_ptid); + const CORE_ADDR addr_trap + = address_significant (gdbarch, (CORE_ADDR) siginfo.si_addr); + /* Check if the address matches any watched address. */ state = aarch64_get_debug_reg_state (inferior_ptid.pid ()); for (i = aarch64_num_wp_regs - 1; i >= 0; --i) @@ -884,7 +891,6 @@ aarch64_linux_nat_target::stopped_data_address (CORE_ADDR *addr_p) const unsigned int offset = aarch64_watchpoint_offset (state->dr_ctrl_wp[i]); const unsigned int len = aarch64_watchpoint_length (state->dr_ctrl_wp[i]); - const CORE_ADDR addr_trap = (CORE_ADDR) siginfo.si_addr; const CORE_ADDR addr_watch = state->dr_addr_wp[i] + offset; const CORE_ADDR addr_watch_aligned = align_down (state->dr_addr_wp[i], 8); const CORE_ADDR addr_orig = state->dr_addr_orig_wp[i]; diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog index 549475a75f..7249ae670d 100644 --- a/gdb/testsuite/ChangeLog +++ b/gdb/testsuite/ChangeLog @@ -1,3 +1,10 @@ +2020-12-16 Luis Machado + + * gdb.arch/aarch64-tagged-pointer.c (main): Add a few more + pointer-based memory accesses. + * gdb.arch/aarch64-tagged-pointer.exp: Exercise additional + hw watchpoint cases. + 2020-12-15 Rae Kim * gdb.base/document.exp: New test. diff --git a/gdb/testsuite/gdb.arch/aarch64-tagged-pointer.c b/gdb/testsuite/gdb.arch/aarch64-tagged-pointer.c index 609d4f220e..658c3093e8 100644 --- a/gdb/testsuite/gdb.arch/aarch64-tagged-pointer.c +++ b/gdb/testsuite/gdb.arch/aarch64-tagged-pointer.c @@ -53,5 +53,11 @@ main (void) } sp1->i = 8765; - i = 1; + sp2->i = 4321; + sp1->i = 8765; + sp2->i = 4321; + *p1 = 1; + *p2 = 2; + *p1 = 1; + *p2 = 2; } diff --git a/gdb/testsuite/gdb.arch/aarch64-tagged-pointer.exp b/gdb/testsuite/gdb.arch/aarch64-tagged-pointer.exp index 957571fdf9..01c2b577d5 100644 --- a/gdb/testsuite/gdb.arch/aarch64-tagged-pointer.exp +++ b/gdb/testsuite/gdb.arch/aarch64-tagged-pointer.exp @@ -92,14 +92,21 @@ foreach_with_prefix bptype {"hbreak" "break"} { gdb_test "down" gdb_test "finish" -# Watch on tagged pointer. -gdb_test "watch *sp2" -gdb_test "continue" \ - "Continuing\\..*Hardware watchpoint \[0-9\]+.*" \ - "run until watchpoint on s1" -delete_breakpoints -gdb_test "watch *p2" -gdb_test "continue" \ - "Continuing\\..*Hardware watchpoint \[0-9\]+.*" \ - "run until watchpoint on i" +# sp1 and p1 are untagged pointers, but sp2 and p2 are tagged pointers. +# Cycle through all of them to make sure the following combinations work: +# +# hw watch on untagged address, hit on untagged address. +# hw watch on tagged address, hit on untagged address. +# hw watch on untagged address, hit on tagged address. +# hw watch on tagged address, hit on tagged address. +foreach symbol {"sp1" "sp2" "p1" "p2"} { + gdb_test "watch *${symbol}" + gdb_test "continue" \ + "Continuing\\..*Hardware watchpoint \[0-9\]+.*" \ + "run until watchpoint on ${symbol}" + gdb_test "continue" \ + "Continuing\\..*Hardware watchpoint \[0-9\]+.*" \ + "run until watchpoint on ${symbol}, 2nd hit" + delete_breakpoints +} diff --git a/gdbserver/ChangeLog b/gdbserver/ChangeLog index 9756d4cada..16a9609bd0 100644 --- a/gdbserver/ChangeLog +++ b/gdbserver/ChangeLog @@ -1,3 +1,8 @@ +2020-12-16 Luis Machado + + * linux-aarch64-low.cc (address_significant): New function. + (aarch64_target::low_stopped_data_address): Handle the TBI. + 2020-12-11 Andrew Burgess * Makefile.in (IPA_LIB): Include libiberty library. diff --git a/gdbserver/linux-aarch64-low.cc b/gdbserver/linux-aarch64-low.cc index 08208ae4f4..f39d7c2316 100644 --- a/gdbserver/linux-aarch64-low.cc +++ b/gdbserver/linux-aarch64-low.cc @@ -458,6 +458,23 @@ aarch64_target::low_remove_point (raw_bkpt_type type, CORE_ADDR addr, return ret; } +/* Return the address only having significant bits. This is used to ignore + the top byte (TBI). */ + +static CORE_ADDR +address_significant (CORE_ADDR addr) +{ + /* Clear insignificant bits of a target address and sign extend resulting + address. */ + int addr_bit = 56; + + CORE_ADDR sign = (CORE_ADDR) 1 << (addr_bit - 1); + addr &= ((CORE_ADDR) 1 << addr_bit) - 1; + addr = (addr ^ sign) - sign; + + return addr; +} + /* Implementation of linux target ops method "low_stopped_data_address". */ CORE_ADDR @@ -478,6 +495,12 @@ aarch64_target::low_stopped_data_address () || (siginfo.si_code & 0xffff) != 0x0004 /* TRAP_HWBKPT */) return (CORE_ADDR) 0; + /* Make sure to ignore the top byte, otherwise we may not recognize a + hardware watchpoint hit. The stopped data addresses coming from the + kernel can potentially be tagged addresses. */ + const CORE_ADDR addr_trap + = address_significant ((CORE_ADDR) siginfo.si_addr); + /* Check if the address matches any watched address. */ state = aarch64_get_debug_reg_state (pid_of (current_thread)); for (i = aarch64_num_wp_regs - 1; i >= 0; --i) @@ -485,7 +508,6 @@ aarch64_target::low_stopped_data_address () const unsigned int offset = aarch64_watchpoint_offset (state->dr_ctrl_wp[i]); const unsigned int len = aarch64_watchpoint_length (state->dr_ctrl_wp[i]); - const CORE_ADDR addr_trap = (CORE_ADDR) siginfo.si_addr; const CORE_ADDR addr_watch = state->dr_addr_wp[i] + offset; const CORE_ADDR addr_watch_aligned = align_down (state->dr_addr_wp[i], 8); const CORE_ADDR addr_orig = state->dr_addr_orig_wp[i];