[v2,PR,gdb/23210] Unset gdbarch significant_addr_bit by default
Commit Message
This version fixes the typo and gdbarch.sh issue highlighted in review.
LGTM?
This patch fixes a bug introduced by fix to AArch64 pointer tagging.
In our fix for tagged pointer support our agreed approach was to sign
extend user-space address after clearing tag bits. This is not same
for all architectures and this patch allows sign extension for
addresses on targets which specifically set significant_addr_bit.
More information about patch that caused the issues and discussion
around tagged pointer support can be found in links below:
https://sourceware.org/ml/gdb-patches/2018-05/msg00000.html
https://sourceware.org/ml/gdb-patches/2017-12/msg00159.html
gdb/ChangeLog:
2018-05-23 Omair Javaid <omair.javaid@linaro.org>
* gdbarch.sh (significant_addr_bit): Default to zero when
not set by target architecture.
* gdbarch.c: Re-generated.
* utils.c (address_significant): Update.
---
gdb/gdbarch.c | 4 ++--
gdb/gdbarch.sh | 2 +-
gdb/utils.c | 5 +++--
3 files changed, 6 insertions(+), 5 deletions(-)
Comments
On 05/26/2018 01:58 AM, Omair Javaid wrote:
> This version fixes the typo and gdbarch.sh issue highlighted in review.
>
> LGTM?
I think the resulting API ends up a little weird. Maybe a better
fit would be something around:
CORE_ADDR gdbarch_canonical_address (gdbarch *, CORE_ADDR addr);
with the default implementation being a nop [return ADDR] while
Aarch64's implementation would clear the tag and sign extend.
Dunno, not sure, I really did not think that through, and, as
I mentioned before, I'm totally OK with this as is, we understand
the issues and can always change it later.
More important right now is unbreaking 32-bit x86 and the branch.
Thus, OK as is. Please push to master and branch.
Thanks,
Pedro Alves
Hi Omar,
On Sat, May 26, 2018 at 05:58:51AM +0500, Omair Javaid wrote:
> This version fixes the typo and gdbarch.sh issue highlighted in review.
>
> LGTM?
>
> This patch fixes a bug introduced by fix to AArch64 pointer tagging.
>
> In our fix for tagged pointer support our agreed approach was to sign
> extend user-space address after clearing tag bits. This is not same
> for all architectures and this patch allows sign extension for
> addresses on targets which specifically set significant_addr_bit.
>
> More information about patch that caused the issues and discussion
> around tagged pointer support can be found in links below:
>
> https://sourceware.org/ml/gdb-patches/2018-05/msg00000.html
> https://sourceware.org/ml/gdb-patches/2017-12/msg00159.html
>
> gdb/ChangeLog:
>
> 2018-05-23 Omair Javaid <omair.javaid@linaro.org>
>
> * gdbarch.sh (significant_addr_bit): Default to zero when
> not set by target architecture.
> * gdbarch.c: Re-generated.
> * utils.c (address_significant): Update.
In addition to Pedro's comments, can you make sure you add "PR
gdb/23210" to the ChangeLog entry?
@@ -615,8 +615,7 @@ verify_gdbarch (struct gdbarch *gdbarch)
/* Skip verify of stabs_argument_has_addr, invalid_p == 0 */
/* Skip verify of convert_from_func_ptr_addr, invalid_p == 0 */
/* Skip verify of addr_bits_remove, invalid_p == 0 */
- if (gdbarch->significant_addr_bit == 0)
- gdbarch->significant_addr_bit = gdbarch_addr_bit (gdbarch);
+ /* Skip verify of significant_addr_bit, invalid_p == 0 */
/* Skip verify of software_single_step, has predicate. */
/* Skip verify of single_step_through_delay, has predicate. */
/* Skip verify of print_insn, invalid_p == 0 */
@@ -3209,6 +3208,7 @@ int
gdbarch_significant_addr_bit (struct gdbarch *gdbarch)
{
gdb_assert (gdbarch != NULL);
+ /* Skip verify of significant_addr_bit, invalid_p == 0 */
if (gdbarch_debug >= 2)
fprintf_unfiltered (gdb_stdlog, "gdbarch_significant_addr_bit called\n");
return gdbarch->significant_addr_bit;
@@ -622,7 +622,7 @@ m;CORE_ADDR;addr_bits_remove;CORE_ADDR addr;addr;;core_addr_identity;;0
# For example, on AArch64, the top bits of an address known as the "tag"
# are ignored by the kernel, the hardware, etc. and can be regarded as
# additional data associated with the address.
-v;int;significant_addr_bit;;;;;gdbarch_addr_bit (gdbarch);
+v;int;significant_addr_bit;;;;;;0
# FIXME/cagney/2001-01-18: This should be split in two. A target method that
# indicates if the target needs software single step. An ISA method to
@@ -2708,10 +2708,11 @@ address_significant (gdbarch *gdbarch, CORE_ADDR addr)
/* Clear insignificant bits of a target address and sign extend resulting
address, avoiding shifts larger or equal than the width of a CORE_ADDR.
The local variable ADDR_BIT stops the compiler reporting a shift overflow
- when it won't occur. */
+ when it won't occur. Skip updating of target address if current target
+ has not set gdbarch significant_addr_bit. */
int addr_bit = gdbarch_significant_addr_bit (gdbarch);
- if (addr_bit < (sizeof (CORE_ADDR) * HOST_CHAR_BIT))
+ if (addr_bit && (addr_bit < (sizeof (CORE_ADDR) * HOST_CHAR_BIT)))
{
CORE_ADDR sign = (CORE_ADDR) 1 << (addr_bit - 1);
addr &= ((CORE_ADDR) 1 << addr_bit) - 1;