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Fix TBI handling for watchpoints

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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  <luis.machado@linaro.org>

	* aarch64-linux-nat.c
	(aarch64_linux_nat_target::stopped_data_address): Handle the TBI.

gdbserver/ChangeLog:

2020-12-16  Luis Machado  <luis.machado@linaro.org>

	* 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  <luis.machado@linaro.org>

	* 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.
This commit is contained in:
Luis Machado 2020-12-10 16:51:20 -03:00
parent c410035d37
commit 19007d9556
7 changed files with 71 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
gdb/ChangeLog
View File

@ -1,3 +1,8 @@
2020-12-16 Luis Machado <luis.machado@linaro.org>
* aarch64-linux-nat.c
(aarch64_linux_nat_target::stopped_data_address): Handle the TBI.
2020-12-15 Rae Kim <rae.kim@gmail.com>
* cli/cli-script.c (do_document_command): Rename from

8
gdb/aarch64-linux-nat.c
View File

@ -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];

7
gdb/testsuite/ChangeLog
View File

@ -1,3 +1,10 @@
2020-12-16 Luis Machado <luis.machado@linaro.org>
* 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 <rae.kim@gmail.com>
* gdb.base/document.exp: New test.

8
gdb/testsuite/gdb.arch/aarch64-tagged-pointer.c
View File

@ -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;
}

27
gdb/testsuite/gdb.arch/aarch64-tagged-pointer.exp
View File

@ -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
}

5
gdbserver/ChangeLog
View File

@ -1,3 +1,8 @@
2020-12-16 Luis Machado <luis.machado@linaro.org>
* linux-aarch64-low.cc (address_significant): New function.
(aarch64_target::low_stopped_data_address): Handle the TBI.
2020-12-11 Andrew Burgess <andrew.burgess@embecosm.com>
* Makefile.in (IPA_LIB): Include libiberty library.

24
gdbserver/linux-aarch64-low.cc
View File

@ -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];