* [PATCH 0/2] Fix gdb.arch/aarch64-sme-core-*.exp failures
@ 2023-11-30 21:20 Simon Marchi
2023-11-30 21:20 ` [PATCH 1/2] gdb: return when exceeding buffer size in regcache::transfer_regset Simon Marchi
2023-11-30 21:20 ` [PATCH 2/2] gdb: add missing regcache_map_entry array null terminators in aarch64-linux-tdep.c Simon Marchi
0 siblings, 2 replies; 10+ messages in thread
From: Simon Marchi @ 2023-11-30 21:20 UTC (permalink / raw)
To: gdb-patches; +Cc: Luis Machado, John Baldwin, Simon Marchi
While testing my pseudo-register series on QEMU AArch64 (to test SVE and
SME support), I noticed some pre-existing failures in the
gdb.arch/aarch64-sme-core-*.exp. This small series fixes them.
Simon Marchi (2):
gdb: return when exceeding buffer size in regcache::transfer_regset
gdb: add missing regcache_map_entry array null terminators in
aarch64-linux-tdep.c
gdb/aarch64-linux-tdep.c | 7 +++++--
gdb/regcache.c | 2 +-
2 files changed, 6 insertions(+), 3 deletions(-)
base-commit: d5835df2eebf8e9cd3ae35b683c831c2a16a5269
--
2.43.0
^ permalink raw reply [flat|nested] 10+ messages in thread
* [PATCH 1/2] gdb: return when exceeding buffer size in regcache::transfer_regset
2023-11-30 21:20 [PATCH 0/2] Fix gdb.arch/aarch64-sme-core-*.exp failures Simon Marchi
@ 2023-11-30 21:20 ` Simon Marchi
2023-11-30 23:42 ` John Baldwin
2023-12-01 9:13 ` Luis Machado
2023-11-30 21:20 ` [PATCH 2/2] gdb: add missing regcache_map_entry array null terminators in aarch64-linux-tdep.c Simon Marchi
1 sibling, 2 replies; 10+ messages in thread
From: Simon Marchi @ 2023-11-30 21:20 UTC (permalink / raw)
To: gdb-patches; +Cc: Luis Machado, John Baldwin, Simon Marchi
regcache::transfer_regset iterates over an array of regcache_map_entry,
transferring the registers (between regcache and buffer) described by
those entries. It stops either when it reaches the end of the
regcache_map_entry array (marked by a null entry) or (it seems like the
intent is) when it reaches the end of the buffer (in which case not all
described registers are transferred).
I said "seems like the intent is", because there appears to be a small
bug. transfer_regset is made of two loops:
foreach regcache_map_entry:
foreach register described by the regcache_map_entry:
if the register doesn't fit in the remainder of the buffer:
break
transfer register
When stopping because we have reached the end of the buffer, the break
only breaks out of the inner loop.
This problem causes some failures when I run tests such as
gdb.arch/aarch64-sme-core-3.exp (on AArch64 Linux, in qemu). This is
partly due to aarch64_linux_iterate_over_regset_sections failing to add
a null terminator in its regcache_map_entry array, but I think there is
still a problem in transfer_regset.
The sequence to the crash is:
- The `regcache_map_entry za_regmap` object built in
aarch64_linux_iterate_over_regset_sections does not have a null
terminator.
- When the target does not have a ZA register,
aarch64_linux_collect_za_regset calls `regcache->collect_regset` with
a size of 0 (it's actually pointless, but still it should work).
- transfer_regset gets called with a buffer size of 0.
- transfer_regset detects that the register to transfer wouldn't fit in
0 bytes, so it breaks out of the inner loop.
- The outer loop tries to go read the next regcache_map_entry, but
there isn't one, and we start reading garbage.
Obviously, this would get fixed by making
aarch64_linux_iterate_over_regset_sections use a null terminator (which
is what the following patch does). But I think that when detecting that
there is not enough buffer left for the current register,
transfer_regset should return, not only break out of the inner loop.
This is a kind of contrived scenario, but imagine we have these two
regcache_map_entry objects:
- 2 registers of 8 bytes
- 2 registers of 4 bytes
For some reason, the caller passes a buffer of 12 bytes.
transfer_regset will detect that the second 8 byte register does not
fit, and break out of the inner loop. However, it will then go try the
next regcache_map_entry. It will see that it can fit one 4 byte
register in the remaining buffer space, and transfer it from/to there.
This is very likely not an expected behavior, we wouldn't expect to
read/write this sequence of registers from/to the buffer.
In this example, whether passing a 12 bytes buffer makes sense or
whether it is a size computation bug in the caller, we don't know, but I
think that exiting as soon as a register doesn't fit is the sane thing
to do.
Change-Id: Ia349627d2e5d281822ade92a8e7a4dea4f839e07
---
gdb/regcache.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/gdb/regcache.c b/gdb/regcache.c
index 9dc354ec2b3a..e46a0b58f505 100644
--- a/gdb/regcache.c
+++ b/gdb/regcache.c
@@ -1208,7 +1208,7 @@ regcache::transfer_regset (const struct regset *regset, int regbase,
for (; count--; regno++, offs += slot_size)
{
if (offs + slot_size > size)
- break;
+ return;
transfer_regset_register (out_regcache, regno, in_buf, out_buf,
slot_size, offs);
--
2.43.0
^ permalink raw reply [flat|nested] 10+ messages in thread
* [PATCH 2/2] gdb: add missing regcache_map_entry array null terminators in aarch64-linux-tdep.c
2023-11-30 21:20 [PATCH 0/2] Fix gdb.arch/aarch64-sme-core-*.exp failures Simon Marchi
2023-11-30 21:20 ` [PATCH 1/2] gdb: return when exceeding buffer size in regcache::transfer_regset Simon Marchi
@ 2023-11-30 21:20 ` Simon Marchi
2023-11-30 23:44 ` John Baldwin
2023-12-01 9:12 ` Luis Machado
1 sibling, 2 replies; 10+ messages in thread
From: Simon Marchi @ 2023-11-30 21:20 UTC (permalink / raw)
To: gdb-patches; +Cc: Luis Machado, John Baldwin, Simon Marchi
Fix two spots in aarch64-linux-tdep.c that build regcache_map_entry
arrays without a null terminator. The null terminators are needed for
regcache::transfer_regset to work properly.
Some shower thoughts: I'm wondering: if a caller uses
supply_regset/collect_regset with a regcache_map_entry array that
describes exactly X bytes, and passes a buffer of X bytes, should a null
terminator really be needed? regcache::transfer_regset could be written
in a way that it exits as soon as the remaining buffer size reaches 0.
Right now, even when it has consumed exactly the X bytes of the buffer,
transfer_regset needs to read the following regcache_map_entry's count
(expected to be 0) to realize it's done. If it exited its outer loop
when `offs == size`, it would remove the need for the null terminator in
this case.
Shower thought #2: we could also bypass that by using array_view to pass
regcache_map_entry arrays, removing the need for null terminators
altogether, but that's a bigger change.
Change-Id: I3224a314e1360b319438f32de8c81e70ab42e105
---
gdb/aarch64-linux-tdep.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
index cd99b33fed25..5be887a9c817 100644
--- a/gdb/aarch64-linux-tdep.c
+++ b/gdb/aarch64-linux-tdep.c
@@ -1497,7 +1497,9 @@ aarch64_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
/* Create this on the fly in order to handle the ZA register size. */
const struct regcache_map_entry za_regmap[] =
{
- { 1, tdep->sme_za_regnum, (int) std::pow (sve_vl_from_vq (tdep->sme_svq), 2) }
+ { 1, tdep->sme_za_regnum,
+ (int) std::pow (sve_vl_from_vq (tdep->sme_svq), 2) },
+ { 0 }
};
const struct regset aarch64_linux_za_regset =
@@ -1518,7 +1520,8 @@ aarch64_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
{
const struct regcache_map_entry zt_regmap[] =
{
- { 1, tdep->sme2_zt0_regnum, AARCH64_SME2_ZT0_SIZE }
+ { 1, tdep->sme2_zt0_regnum, AARCH64_SME2_ZT0_SIZE },
+ { 0 }
};
/* We set the register set size to REGSET_VARIABLE_SIZE here because
--
2.43.0
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 1/2] gdb: return when exceeding buffer size in regcache::transfer_regset
2023-11-30 21:20 ` [PATCH 1/2] gdb: return when exceeding buffer size in regcache::transfer_regset Simon Marchi
@ 2023-11-30 23:42 ` John Baldwin
2023-12-01 0:02 ` Simon Marchi
2023-12-01 9:13 ` Luis Machado
1 sibling, 1 reply; 10+ messages in thread
From: John Baldwin @ 2023-11-30 23:42 UTC (permalink / raw)
To: Simon Marchi, gdb-patches; +Cc: Luis Machado
On 11/30/23 1:20 PM, Simon Marchi wrote:
> regcache::transfer_regset iterates over an array of regcache_map_entry,
> transferring the registers (between regcache and buffer) described by
> those entries. It stops either when it reaches the end of the
> regcache_map_entry array (marked by a null entry) or (it seems like the
> intent is) when it reaches the end of the buffer (in which case not all
> described registers are transferred).
>
> I said "seems like the intent is", because there appears to be a small
> bug. transfer_regset is made of two loops:
>
> foreach regcache_map_entry:
> foreach register described by the regcache_map_entry:
> if the register doesn't fit in the remainder of the buffer:
> break
>
> transfer register
>
> When stopping because we have reached the end of the buffer, the break
> only breaks out of the inner loop.
>
> This problem causes some failures when I run tests such as
> gdb.arch/aarch64-sme-core-3.exp (on AArch64 Linux, in qemu). This is
> partly due to aarch64_linux_iterate_over_regset_sections failing to add
> a null terminator in its regcache_map_entry array, but I think there is
> still a problem in transfer_regset.
>
> The sequence to the crash is:
>
> - The `regcache_map_entry za_regmap` object built in
> aarch64_linux_iterate_over_regset_sections does not have a null
> terminator.
> - When the target does not have a ZA register,
> aarch64_linux_collect_za_regset calls `regcache->collect_regset` with
> a size of 0 (it's actually pointless, but still it should work).
> - transfer_regset gets called with a buffer size of 0.
> - transfer_regset detects that the register to transfer wouldn't fit in
> 0 bytes, so it breaks out of the inner loop.
> - The outer loop tries to go read the next regcache_map_entry, but
> there isn't one, and we start reading garbage.
>
> Obviously, this would get fixed by making
> aarch64_linux_iterate_over_regset_sections use a null terminator (which
> is what the following patch does). But I think that when detecting that
> there is not enough buffer left for the current register,
> transfer_regset should return, not only break out of the inner loop.
>
> This is a kind of contrived scenario, but imagine we have these two
> regcache_map_entry objects:
>
> - 2 registers of 8 bytes
> - 2 registers of 4 bytes
>
> For some reason, the caller passes a buffer of 12 bytes.
> transfer_regset will detect that the second 8 byte register does not
> fit, and break out of the inner loop. However, it will then go try the
> next regcache_map_entry. It will see that it can fit one 4 byte
> register in the remaining buffer space, and transfer it from/to there.
> This is very likely not an expected behavior, we wouldn't expect to
> read/write this sequence of registers from/to the buffer.
>
> In this example, whether passing a 12 bytes buffer makes sense or
> whether it is a size computation bug in the caller, we don't know, but I
> think that exiting as soon as a register doesn't fit is the sane thing
> to do.
>
> Change-Id: Ia349627d2e5d281822ade92a8e7a4dea4f839e07
> ---
> gdb/regcache.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/gdb/regcache.c b/gdb/regcache.c
> index 9dc354ec2b3a..e46a0b58f505 100644
> --- a/gdb/regcache.c
> +++ b/gdb/regcache.c
> @@ -1208,7 +1208,7 @@ regcache::transfer_regset (const struct regset *regset, int regbase,
> for (; count--; regno++, offs += slot_size)
> {
> if (offs + slot_size > size)
> - break;
> + return;
>
> transfer_regset_register (out_regcache, regno, in_buf, out_buf,
> slot_size, offs);
This makes sense to me. In particular, note that a few lines below we do a
return for the same condition when an individual register doesn't fit.
Reviewed-By: John Baldwin <jhb@FreeBSD.org>
--
John Baldwin
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 2/2] gdb: add missing regcache_map_entry array null terminators in aarch64-linux-tdep.c
2023-11-30 21:20 ` [PATCH 2/2] gdb: add missing regcache_map_entry array null terminators in aarch64-linux-tdep.c Simon Marchi
@ 2023-11-30 23:44 ` John Baldwin
2023-12-01 0:03 ` Simon Marchi
2023-12-01 9:12 ` Luis Machado
1 sibling, 1 reply; 10+ messages in thread
From: John Baldwin @ 2023-11-30 23:44 UTC (permalink / raw)
To: Simon Marchi, gdb-patches; +Cc: Luis Machado
On 11/30/23 1:20 PM, Simon Marchi wrote:
> Fix two spots in aarch64-linux-tdep.c that build regcache_map_entry
> arrays without a null terminator. The null terminators are needed for
> regcache::transfer_regset to work properly.
>
> Some shower thoughts: I'm wondering: if a caller uses
> supply_regset/collect_regset with a regcache_map_entry array that
> describes exactly X bytes, and passes a buffer of X bytes, should a null
> terminator really be needed? regcache::transfer_regset could be written
> in a way that it exits as soon as the remaining buffer size reaches 0.
> Right now, even when it has consumed exactly the X bytes of the buffer,
> transfer_regset needs to read the following regcache_map_entry's count
> (expected to be 0) to realize it's done. If it exited its outer loop
> when `offs == size`, it would remove the need for the null terminator in
> this case.
regcache_map_entry_size depends on a nul terminator as it is computing a
size, not taking a register block size as input.
> Shower thought #2: we could also bypass that by using array_view to pass
> regcache_map_entry arrays, removing the need for null terminators
> altogether, but that's a bigger change.
I do think this is the better long-term solution.
> Change-Id: I3224a314e1360b319438f32de8c81e70ab42e105
> ---
> gdb/aarch64-linux-tdep.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
> index cd99b33fed25..5be887a9c817 100644
> --- a/gdb/aarch64-linux-tdep.c
> +++ b/gdb/aarch64-linux-tdep.c
> @@ -1497,7 +1497,9 @@ aarch64_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
> /* Create this on the fly in order to handle the ZA register size. */
> const struct regcache_map_entry za_regmap[] =
> {
> - { 1, tdep->sme_za_regnum, (int) std::pow (sve_vl_from_vq (tdep->sme_svq), 2) }
> + { 1, tdep->sme_za_regnum,
> + (int) std::pow (sve_vl_from_vq (tdep->sme_svq), 2) },
> + { 0 }
> };
>
> const struct regset aarch64_linux_za_regset =
> @@ -1518,7 +1520,8 @@ aarch64_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
> {
> const struct regcache_map_entry zt_regmap[] =
> {
> - { 1, tdep->sme2_zt0_regnum, AARCH64_SME2_ZT0_SIZE }
> + { 1, tdep->sme2_zt0_regnum, AARCH64_SME2_ZT0_SIZE },
> + { 0 }
> };
>
> /* We set the register set size to REGSET_VARIABLE_SIZE here because
Reviewed-By: John Baldwin <jhb@FreeBSD.org>
--
John Baldwin
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 1/2] gdb: return when exceeding buffer size in regcache::transfer_regset
2023-11-30 23:42 ` John Baldwin
@ 2023-12-01 0:02 ` Simon Marchi
0 siblings, 0 replies; 10+ messages in thread
From: Simon Marchi @ 2023-12-01 0:02 UTC (permalink / raw)
To: John Baldwin, Simon Marchi, gdb-patches; +Cc: Luis Machado
On 2023-11-30 18:42, John Baldwin wrote:
> On 11/30/23 1:20 PM, Simon Marchi wrote:
>> regcache::transfer_regset iterates over an array of regcache_map_entry,
>> transferring the registers (between regcache and buffer) described by
>> those entries. It stops either when it reaches the end of the
>> regcache_map_entry array (marked by a null entry) or (it seems like the
>> intent is) when it reaches the end of the buffer (in which case not all
>> described registers are transferred).
>>
>> I said "seems like the intent is", because there appears to be a small
>> bug. transfer_regset is made of two loops:
>>
>> foreach regcache_map_entry:
>> foreach register described by the regcache_map_entry:
>> if the register doesn't fit in the remainder of the buffer:
>> break
>>
>> transfer register
>>
>> When stopping because we have reached the end of the buffer, the break
>> only breaks out of the inner loop.
>>
>> This problem causes some failures when I run tests such as
>> gdb.arch/aarch64-sme-core-3.exp (on AArch64 Linux, in qemu). This is
>> partly due to aarch64_linux_iterate_over_regset_sections failing to add
>> a null terminator in its regcache_map_entry array, but I think there is
>> still a problem in transfer_regset.
>>
>> The sequence to the crash is:
>>
>> - The `regcache_map_entry za_regmap` object built in
>> aarch64_linux_iterate_over_regset_sections does not have a null
>> terminator.
>> - When the target does not have a ZA register,
>> aarch64_linux_collect_za_regset calls `regcache->collect_regset` with
>> a size of 0 (it's actually pointless, but still it should work).
>> - transfer_regset gets called with a buffer size of 0.
>> - transfer_regset detects that the register to transfer wouldn't fit in
>> 0 bytes, so it breaks out of the inner loop.
>> - The outer loop tries to go read the next regcache_map_entry, but
>> there isn't one, and we start reading garbage.
>>
>> Obviously, this would get fixed by making
>> aarch64_linux_iterate_over_regset_sections use a null terminator (which
>> is what the following patch does). But I think that when detecting that
>> there is not enough buffer left for the current register,
>> transfer_regset should return, not only break out of the inner loop.
>>
>> This is a kind of contrived scenario, but imagine we have these two
>> regcache_map_entry objects:
>>
>> - 2 registers of 8 bytes
>> - 2 registers of 4 bytes
>>
>> For some reason, the caller passes a buffer of 12 bytes.
>> transfer_regset will detect that the second 8 byte register does not
>> fit, and break out of the inner loop. However, it will then go try the
>> next regcache_map_entry. It will see that it can fit one 4 byte
>> register in the remaining buffer space, and transfer it from/to there.
>> This is very likely not an expected behavior, we wouldn't expect to
>> read/write this sequence of registers from/to the buffer.
>>
>> In this example, whether passing a 12 bytes buffer makes sense or
>> whether it is a size computation bug in the caller, we don't know, but I
>> think that exiting as soon as a register doesn't fit is the sane thing
>> to do.
>>
>> Change-Id: Ia349627d2e5d281822ade92a8e7a4dea4f839e07
>> ---
>> gdb/regcache.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/gdb/regcache.c b/gdb/regcache.c
>> index 9dc354ec2b3a..e46a0b58f505 100644
>> --- a/gdb/regcache.c
>> +++ b/gdb/regcache.c
>> @@ -1208,7 +1208,7 @@ regcache::transfer_regset (const struct regset *regset, int regbase,
>> for (; count--; regno++, offs += slot_size)
>> {
>> if (offs + slot_size > size)
>> - break;
>> + return;
>> transfer_regset_register (out_regcache, regno, in_buf, out_buf,
>> slot_size, offs);
>
> This makes sense to me. In particular, note that a few lines below we do a
> return for the same condition when an individual register doesn't fit.
Yeah, although it could be argued that this case is different: we're
targetting a single register, we found the regcache_map_entry that
describes that register, so regardless of the outcome, we know we don't
want to keep searching the regmap array.
> Reviewed-By: John Baldwin <jhb@FreeBSD.org>
Thanks, will add the trailer.
Simon
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 2/2] gdb: add missing regcache_map_entry array null terminators in aarch64-linux-tdep.c
2023-11-30 23:44 ` John Baldwin
@ 2023-12-01 0:03 ` Simon Marchi
0 siblings, 0 replies; 10+ messages in thread
From: Simon Marchi @ 2023-12-01 0:03 UTC (permalink / raw)
To: John Baldwin, Simon Marchi, gdb-patches; +Cc: Luis Machado
On 2023-11-30 18:44, John Baldwin wrote:
> On 11/30/23 1:20 PM, Simon Marchi wrote:
>> Fix two spots in aarch64-linux-tdep.c that build regcache_map_entry
>> arrays without a null terminator. The null terminators are needed for
>> regcache::transfer_regset to work properly.
>>
>> Some shower thoughts: I'm wondering: if a caller uses
>> supply_regset/collect_regset with a regcache_map_entry array that
>> describes exactly X bytes, and passes a buffer of X bytes, should a null
>> terminator really be needed? regcache::transfer_regset could be written
>> in a way that it exits as soon as the remaining buffer size reaches 0.
>> Right now, even when it has consumed exactly the X bytes of the buffer,
>> transfer_regset needs to read the following regcache_map_entry's count
>> (expected to be 0) to realize it's done. If it exited its outer loop
>> when `offs == size`, it would remove the need for the null terminator in
>> this case.
>
> regcache_map_entry_size depends on a nul terminator as it is computing a
> size, not taking a register block size as input.
Good point, thanks. That settles that regcache_map_entry arrays need a
null terminator to be valid.
>> Shower thought #2: we could also bypass that by using array_view to pass
>> regcache_map_entry arrays, removing the need for null terminators
>> altogether, but that's a bigger change.
>
> I do think this is the better long-term solution.
>
>> Change-Id: I3224a314e1360b319438f32de8c81e70ab42e105
>> ---
>> gdb/aarch64-linux-tdep.c | 7 +++++--
>> 1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
>> index cd99b33fed25..5be887a9c817 100644
>> --- a/gdb/aarch64-linux-tdep.c
>> +++ b/gdb/aarch64-linux-tdep.c
>> @@ -1497,7 +1497,9 @@ aarch64_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
>> /* Create this on the fly in order to handle the ZA register size. */
>> const struct regcache_map_entry za_regmap[] =
>> {
>> - { 1, tdep->sme_za_regnum, (int) std::pow (sve_vl_from_vq (tdep->sme_svq), 2) }
>> + { 1, tdep->sme_za_regnum,
>> + (int) std::pow (sve_vl_from_vq (tdep->sme_svq), 2) },
>> + { 0 }
>> };
>> const struct regset aarch64_linux_za_regset =
>> @@ -1518,7 +1520,8 @@ aarch64_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
>> {
>> const struct regcache_map_entry zt_regmap[] =
>> {
>> - { 1, tdep->sme2_zt0_regnum, AARCH64_SME2_ZT0_SIZE }
>> + { 1, tdep->sme2_zt0_regnum, AARCH64_SME2_ZT0_SIZE },
>> + { 0 }
>> };
>> /* We set the register set size to REGSET_VARIABLE_SIZE here because
>
> Reviewed-By: John Baldwin <jhb@FreeBSD.org>
Thanks for the review. I will wait for feedback from Luis, since this
concerns AArch64.
Simon
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 2/2] gdb: add missing regcache_map_entry array null terminators in aarch64-linux-tdep.c
2023-11-30 21:20 ` [PATCH 2/2] gdb: add missing regcache_map_entry array null terminators in aarch64-linux-tdep.c Simon Marchi
2023-11-30 23:44 ` John Baldwin
@ 2023-12-01 9:12 ` Luis Machado
2023-12-01 16:21 ` Simon Marchi
1 sibling, 1 reply; 10+ messages in thread
From: Luis Machado @ 2023-12-01 9:12 UTC (permalink / raw)
To: Simon Marchi, gdb-patches; +Cc: John Baldwin
Hi Simon,
On 11/30/23 21:20, Simon Marchi wrote:
> Fix two spots in aarch64-linux-tdep.c that build regcache_map_entry
> arrays without a null terminator. The null terminators are needed for
> regcache::transfer_regset to work properly.
>
> Some shower thoughts: I'm wondering: if a caller uses
> supply_regset/collect_regset with a regcache_map_entry array that
> describes exactly X bytes, and passes a buffer of X bytes, should a null
> terminator really be needed? regcache::transfer_regset could be written
> in a way that it exits as soon as the remaining buffer size reaches 0.
> Right now, even when it has consumed exactly the X bytes of the buffer,
> transfer_regset needs to read the following regcache_map_entry's count
> (expected to be 0) to realize it's done. If it exited its outer loop
> when `offs == size`, it would remove the need for the null terminator in
> this case.
>
> Shower thought #2: we could also bypass that by using array_view to pass
> regcache_map_entry arrays, removing the need for null terminators
> altogether, but that's a bigger change.
>
> Change-Id: I3224a314e1360b319438f32de8c81e70ab42e105
> ---
> gdb/aarch64-linux-tdep.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
> index cd99b33fed25..5be887a9c817 100644
> --- a/gdb/aarch64-linux-tdep.c
> +++ b/gdb/aarch64-linux-tdep.c
> @@ -1497,7 +1497,9 @@ aarch64_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
> /* Create this on the fly in order to handle the ZA register size. */
> const struct regcache_map_entry za_regmap[] =
> {
> - { 1, tdep->sme_za_regnum, (int) std::pow (sve_vl_from_vq (tdep->sme_svq), 2) }
> + { 1, tdep->sme_za_regnum,
> + (int) std::pow (sve_vl_from_vq (tdep->sme_svq), 2) },
> + { 0 }
> };
>
> const struct regset aarch64_linux_za_regset =
> @@ -1518,7 +1520,8 @@ aarch64_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
> {
> const struct regcache_map_entry zt_regmap[] =
> {
> - { 1, tdep->sme2_zt0_regnum, AARCH64_SME2_ZT0_SIZE }
> + { 1, tdep->sme2_zt0_regnum, AARCH64_SME2_ZT0_SIZE },
> + { 0 }
> };
>
> /* We set the register set size to REGSET_VARIABLE_SIZE here because
Yeah, that was a silly mistake. Glad it was spotted.
I failed to spot the missing terminators for these two regcache_map_entry's,
as I see them in other regcache_map_entry's.
This is OK, thanks!
Approved-By: Luis Machado <luis.machado@arm.com>
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 1/2] gdb: return when exceeding buffer size in regcache::transfer_regset
2023-11-30 21:20 ` [PATCH 1/2] gdb: return when exceeding buffer size in regcache::transfer_regset Simon Marchi
2023-11-30 23:42 ` John Baldwin
@ 2023-12-01 9:13 ` Luis Machado
1 sibling, 0 replies; 10+ messages in thread
From: Luis Machado @ 2023-12-01 9:13 UTC (permalink / raw)
To: Simon Marchi, gdb-patches; +Cc: John Baldwin
On 11/30/23 21:20, Simon Marchi wrote:
> regcache::transfer_regset iterates over an array of regcache_map_entry,
> transferring the registers (between regcache and buffer) described by
> those entries. It stops either when it reaches the end of the
> regcache_map_entry array (marked by a null entry) or (it seems like the
> intent is) when it reaches the end of the buffer (in which case not all
> described registers are transferred).
>
> I said "seems like the intent is", because there appears to be a small
> bug. transfer_regset is made of two loops:
>
> foreach regcache_map_entry:
> foreach register described by the regcache_map_entry:
> if the register doesn't fit in the remainder of the buffer:
> break
>
> transfer register
>
> When stopping because we have reached the end of the buffer, the break
> only breaks out of the inner loop.
>
> This problem causes some failures when I run tests such as
> gdb.arch/aarch64-sme-core-3.exp (on AArch64 Linux, in qemu). This is
> partly due to aarch64_linux_iterate_over_regset_sections failing to add
> a null terminator in its regcache_map_entry array, but I think there is
> still a problem in transfer_regset.
>
> The sequence to the crash is:
>
> - The `regcache_map_entry za_regmap` object built in
> aarch64_linux_iterate_over_regset_sections does not have a null
> terminator.
> - When the target does not have a ZA register,
> aarch64_linux_collect_za_regset calls `regcache->collect_regset` with
> a size of 0 (it's actually pointless, but still it should work).
> - transfer_regset gets called with a buffer size of 0.
> - transfer_regset detects that the register to transfer wouldn't fit in
> 0 bytes, so it breaks out of the inner loop.
> - The outer loop tries to go read the next regcache_map_entry, but
> there isn't one, and we start reading garbage.
>
> Obviously, this would get fixed by making
> aarch64_linux_iterate_over_regset_sections use a null terminator (which
> is what the following patch does). But I think that when detecting that
> there is not enough buffer left for the current register,
> transfer_regset should return, not only break out of the inner loop.
>
> This is a kind of contrived scenario, but imagine we have these two
> regcache_map_entry objects:
>
> - 2 registers of 8 bytes
> - 2 registers of 4 bytes
>
> For some reason, the caller passes a buffer of 12 bytes.
> transfer_regset will detect that the second 8 byte register does not
> fit, and break out of the inner loop. However, it will then go try the
> next regcache_map_entry. It will see that it can fit one 4 byte
> register in the remaining buffer space, and transfer it from/to there.
> This is very likely not an expected behavior, we wouldn't expect to
> read/write this sequence of registers from/to the buffer.
>
> In this example, whether passing a 12 bytes buffer makes sense or
> whether it is a size computation bug in the caller, we don't know, but I
> think that exiting as soon as a register doesn't fit is the sane thing
> to do.
>
> Change-Id: Ia349627d2e5d281822ade92a8e7a4dea4f839e07
> ---
> gdb/regcache.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/gdb/regcache.c b/gdb/regcache.c
> index 9dc354ec2b3a..e46a0b58f505 100644
> --- a/gdb/regcache.c
> +++ b/gdb/regcache.c
> @@ -1208,7 +1208,7 @@ regcache::transfer_regset (const struct regset *regset, int regbase,
> for (; count--; regno++, offs += slot_size)
> {
> if (offs + slot_size > size)
> - break;
> + return;
>
> transfer_regset_register (out_regcache, regno, in_buf, out_buf,
> slot_size, offs);
LGTM.
Reviewed-By: Luis Machado <luis.machado@arm.com>
^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: [PATCH 2/2] gdb: add missing regcache_map_entry array null terminators in aarch64-linux-tdep.c
2023-12-01 9:12 ` Luis Machado
@ 2023-12-01 16:21 ` Simon Marchi
0 siblings, 0 replies; 10+ messages in thread
From: Simon Marchi @ 2023-12-01 16:21 UTC (permalink / raw)
To: Luis Machado, Simon Marchi, gdb-patches; +Cc: John Baldwin
On 12/1/23 04:12, Luis Machado wrote:
> Hi Simon,
>
> On 11/30/23 21:20, Simon Marchi wrote:
>> Fix two spots in aarch64-linux-tdep.c that build regcache_map_entry
>> arrays without a null terminator. The null terminators are needed for
>> regcache::transfer_regset to work properly.
>>
>> Some shower thoughts: I'm wondering: if a caller uses
>> supply_regset/collect_regset with a regcache_map_entry array that
>> describes exactly X bytes, and passes a buffer of X bytes, should a null
>> terminator really be needed? regcache::transfer_regset could be written
>> in a way that it exits as soon as the remaining buffer size reaches 0.
>> Right now, even when it has consumed exactly the X bytes of the buffer,
>> transfer_regset needs to read the following regcache_map_entry's count
>> (expected to be 0) to realize it's done. If it exited its outer loop
>> when `offs == size`, it would remove the need for the null terminator in
>> this case.
>>
>> Shower thought #2: we could also bypass that by using array_view to pass
>> regcache_map_entry arrays, removing the need for null terminators
>> altogether, but that's a bigger change.
>>
>> Change-Id: I3224a314e1360b319438f32de8c81e70ab42e105
>> ---
>> gdb/aarch64-linux-tdep.c | 7 +++++--
>> 1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
>> index cd99b33fed25..5be887a9c817 100644
>> --- a/gdb/aarch64-linux-tdep.c
>> +++ b/gdb/aarch64-linux-tdep.c
>> @@ -1497,7 +1497,9 @@ aarch64_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
>> /* Create this on the fly in order to handle the ZA register size. */
>> const struct regcache_map_entry za_regmap[] =
>> {
>> - { 1, tdep->sme_za_regnum, (int) std::pow (sve_vl_from_vq (tdep->sme_svq), 2) }
>> + { 1, tdep->sme_za_regnum,
>> + (int) std::pow (sve_vl_from_vq (tdep->sme_svq), 2) },
>> + { 0 }
>> };
>>
>> const struct regset aarch64_linux_za_regset =
>> @@ -1518,7 +1520,8 @@ aarch64_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
>> {
>> const struct regcache_map_entry zt_regmap[] =
>> {
>> - { 1, tdep->sme2_zt0_regnum, AARCH64_SME2_ZT0_SIZE }
>> + { 1, tdep->sme2_zt0_regnum, AARCH64_SME2_ZT0_SIZE },
>> + { 0 }
>> };
>>
>> /* We set the register set size to REGSET_VARIABLE_SIZE here because
>
> Yeah, that was a silly mistake. Glad it was spotted.
>
> I failed to spot the missing terminators for these two regcache_map_entry's,
> as I see them in other regcache_map_entry's.
>
> This is OK, thanks!
>
> Approved-By: Luis Machado <luis.machado@arm.com>
Thanks, pushed both patches.
Simon
^ permalink raw reply [flat|nested] 10+ messages in thread
end of thread, other threads:[~2023-12-01 16:21 UTC | newest]
Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
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2023-11-30 21:20 [PATCH 0/2] Fix gdb.arch/aarch64-sme-core-*.exp failures Simon Marchi
2023-11-30 21:20 ` [PATCH 1/2] gdb: return when exceeding buffer size in regcache::transfer_regset Simon Marchi
2023-11-30 23:42 ` John Baldwin
2023-12-01 0:02 ` Simon Marchi
2023-12-01 9:13 ` Luis Machado
2023-11-30 21:20 ` [PATCH 2/2] gdb: add missing regcache_map_entry array null terminators in aarch64-linux-tdep.c Simon Marchi
2023-11-30 23:44 ` John Baldwin
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