* [PATCH] gdb.python/py-unwind: Disable stack protection
@ 2017-07-14 10:27 Simon Marchi
2017-07-14 10:30 ` [PATCH v2] " Simon Marchi
0 siblings, 1 reply; 4+ messages in thread
From: Simon Marchi @ 2017-07-14 10:27 UTC (permalink / raw)
To: gdb-patches; +Cc: Simon Marchi
I see the following failure on Ubuntu 16.04's gcc 5.4.0:
Running /home/emaisin/src/binutils-gdb/gdb/testsuite/gdb.python/py-unwind.exp ...
FAIL: gdb.python/py-unwind.exp: continue to breakpoint: break backtrace-broken
FAIL: gdb.python/py-unwind.exp: Backtrace restored by unwinder (pattern 1)
The problem is that the test expects a very particular stack layout.
When stack protection is enabled, it adds a canary value which looks
like an additional local variable. This makes the test complain about
a bad stack layout and fail.
The simple solution is to disable stack protection for that test using
-fno-stack-protector. I checked older compilers (gcc 4.4, clang 3.5)
and they support that flag, so I don't think it's necessary to probe for
whether the compiler supports it.
Maybe a better solution would be to change the test to make it cope with
different stack layouts (perhaps it could save addresses of stuff in
some global variables which GDB/the unwinder would read). I'll go with
the simple solution for now though.
gdb/testsuite/ChangeLog:
* gdb.python/py-unwind.exp: Disable stack protection when
building test file.
---
gdb/testsuite/gdb.python/py-unwind.exp | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/gdb/testsuite/gdb.python/py-unwind.exp b/gdb/testsuite/gdb.python/py-unwind.exp
index 625b04c..4a64f15 100644
--- a/gdb/testsuite/gdb.python/py-unwind.exp
+++ b/gdb/testsuite/gdb.python/py-unwind.exp
@@ -20,7 +20,12 @@ load_lib gdb-python.exp
standard_testfile
-if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile}] } {
+# Stack protection can make the stack look a bit different, breaking the
+# assumptions of this test about the stack lay out.
+
+set flags "additional_flags=-fno-stack-protector"
+
+if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile} "debug $flags"] } {
return -1
}
--
2.7.4
^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH v2] gdb.python/py-unwind: Disable stack protection
2017-07-14 10:27 [PATCH] gdb.python/py-unwind: Disable stack protection Simon Marchi
@ 2017-07-14 10:30 ` Simon Marchi
2017-07-19 10:09 ` Yao Qi
0 siblings, 1 reply; 4+ messages in thread
From: Simon Marchi @ 2017-07-14 10:30 UTC (permalink / raw)
To: gdb-patches; +Cc: Simon Marchi
[I made some typo fixes but forgot to amend my commit before sending the patch,
hence this v2.]
I see the following failure on Ubuntu 16.04's gcc 5.4.0:
Running /home/emaisin/src/binutils-gdb/gdb/testsuite/gdb.python/py-unwind.exp ...
FAIL: gdb.python/py-unwind.exp: continue to breakpoint: break backtrace-broken
FAIL: gdb.python/py-unwind.exp: Backtrace restored by unwinder (pattern 1)
The problem is that the test expects a very particular stack layout.
When stack protection is enabled, it adds a canary value which looks
like an additional local variable. This makes the test complain about
a bad stack layout and fail.
The simple solution is to disable stack protection for that test using
-fno-stack-protector. I checked older compilers (gcc 4.4, clang 3.5)
and they support that flag, so I don't think it's necessary to probe for
whether the compiler supports it.
Maybe a better solution would be to change the test to make it cope with
different stack layouts (perhaps it could save addresses of stuff in
some global variables which GDB/the unwinder would read). I'll go with
the simple solution for now though.
gdb/testsuite/ChangeLog:
* gdb.python/py-unwind.exp: Disable stack protection when
building test file.
---
gdb/testsuite/gdb.python/py-unwind.exp | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/gdb/testsuite/gdb.python/py-unwind.exp b/gdb/testsuite/gdb.python/py-unwind.exp
index 625b04c..86e695c 100644
--- a/gdb/testsuite/gdb.python/py-unwind.exp
+++ b/gdb/testsuite/gdb.python/py-unwind.exp
@@ -20,7 +20,12 @@ load_lib gdb-python.exp
standard_testfile
-if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile}] } {
+# Stack protection can make the stack look a bit different, breaking the
+# assumptions this test has about its layout.
+
+set flags "additional_flags=-fno-stack-protector"
+
+if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile} "debug $flags"] } {
return -1
}
--
2.7.4
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] gdb.python/py-unwind: Disable stack protection
2017-07-14 10:30 ` [PATCH v2] " Simon Marchi
@ 2017-07-19 10:09 ` Yao Qi
2017-07-21 21:59 ` Simon Marchi
0 siblings, 1 reply; 4+ messages in thread
From: Yao Qi @ 2017-07-19 10:09 UTC (permalink / raw)
To: Simon Marchi; +Cc: gdb-patches
Simon Marchi <simon.marchi@ericsson.com> writes:
> Maybe a better solution would be to change the test to make it cope with
> different stack layouts (perhaps it could save addresses of stuff in
> some global variables which GDB/the unwinder would read). I'll go with
> the simple solution for now though.
I prefer moving this test to unit test, and the input is a series of
instructions (copied from py-unwind.exe). The unit test or self test can
somehow test python unwinder works as expected.
>
> gdb/testsuite/ChangeLog:
>
> * gdb.python/py-unwind.exp: Disable stack protection when
> building test file.
The patch is good to me, but I think the test itself is still a little
fragile.
--
Yao (齐尧)
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] gdb.python/py-unwind: Disable stack protection
2017-07-19 10:09 ` Yao Qi
@ 2017-07-21 21:59 ` Simon Marchi
0 siblings, 0 replies; 4+ messages in thread
From: Simon Marchi @ 2017-07-21 21:59 UTC (permalink / raw)
To: Yao Qi; +Cc: Simon Marchi, gdb-patches
On 2017-07-19 12:09, Yao Qi wrote:
> Simon Marchi <simon.marchi@ericsson.com> writes:
>
>> Maybe a better solution would be to change the test to make it cope
>> with
>> different stack layouts (perhaps it could save addresses of stuff in
>> some global variables which GDB/the unwinder would read). I'll go
>> with
>> the simple solution for now though.
>
> I prefer moving this test to unit test, and the input is a series of
> instructions (copied from py-unwind.exe). The unit test or self test
> can
> somehow test python unwinder works as expected.
Ok, I take a note to try that eventually.
>> gdb/testsuite/ChangeLog:
>>
>> * gdb.python/py-unwind.exp: Disable stack protection when
>> building test file.
>
> The patch is good to me, but I think the test itself is still a little
> fragile.
Yes, it's still very fragile. I'll push the current patch anyhow, since
it fixes it for now.
Thanks,
Simon
^ permalink raw reply [flat|nested] 4+ messages in thread
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2017-07-14 10:27 [PATCH] gdb.python/py-unwind: Disable stack protection Simon Marchi
2017-07-14 10:30 ` [PATCH v2] " Simon Marchi
2017-07-19 10:09 ` Yao Qi
2017-07-21 21:59 ` Simon Marchi
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