Re: [Valgrind-developers] Bug 345928: Fix regtest threadname on amd64 / Fix problem with short stacks

[Philippe W. <phi...@sk...>]

On Fri, 2015-04-10 at 06:47 +0200, Matthias Schwarzott wrote:

> The check "if (fp_min + 256 >= fp_max)" in coregrind/m_stacktrace.c:501
> is triggered here.
> 
> By changing it to "if (fp_min + 128 >= fp_max)" it can be fixed.
> 
> I think amd64 is having problems here because some functions do not need
> additional local variables but can use the redzone, so the stackframes
> are small.
Thanks for this analysis.
Some days ago, I looked at the history of this check.
I saw that the value was already decreased in the past for amd64.
This check is also disabled for Darwin.

For x86/ppc32/ppc64/arm/arm64, the value is still 512.

s390x/mips32/mips64/tilegx have no such condition.


It is not clear to me what is the purpose of this check.
I did not find an explanation in the svn history.

I am wondering if that had not as objective to avoid SEGV for bogus
stack pointers.
There was some recent work done to avoid SEGV (e.g. by obtaining
better stack limits for unwinding).

So, I am not sure that these checks are still useful.
Rather, they might only harm in case we have small but valid
stack frames.

Philippe