[RFC PATCH 0/1] add Valgrind hint in kvm_get_one_reg()

[Daniel Henrique Barboza]

Hi,

Valgrind is not happy with how we're using KVM functions that receives a
parameter via reference and write them. This results in a lot of
complaints about uninitialized values when using these functions
because, as default, Valgrind doesn't know that the variable is being
initialized in the function.

This is the overall pattern that Valgrind does not like:

---
uint64_t val;
(...)
kvm_get_one_reg(...., &val);

if (val) {...}
---

Valgrind complains that the 'if' clause is using an uninitialized
variable.

A quick fix is to init 'val' and be done with it. The drawback is that
every single caller of kvm_get_one_reg() must also be bothered with
initializing these variables to avoid the warnings.

David suggested in [1] that, instead, we should add a Valgrind hint in
the common KVM functions to fix this issue for everyone. This is what
this patch accomplishes. kvm_get_one_reg() has 20+ callers so I believe
this extra boilerplate is worth the benefits.

There are more common instances of KVM functions that Valgrind complains
about. If we're good with the approach taken here we can think about
adding this hint for more functions.


[1] https://lists.gnu.org/archive/html/qemu-devel/2022-03/msg07351.html

Daniel Henrique Barboza (1):
  kvm-all.c: hint Valgrind that kvm_get_one_reg() inits memory

 accel/kvm/kvm-all.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

-- 
2.35.1