Fix incorrect lru_cache usage

[borismol]

Fix incorrect lru_cache usage

Description/Motivation/Screenshots

• Removed @lru_cache for gef_disassemble since it returns generator and repetitive context_code shows empty code
• Added get_register_for_selected_frame to correctly cache register values depending on selected frame.

How Has This Been Tested?

Architecture	Yes/No	Comments
x86-32	✖️
x86-64	✔️
ARM	✖️
AARCH64	✖️
MIPS	✖️
POWERPC	✖️
SPARC	✖️
RISC-V	✖️
make tests	✔️

Checklist

• My PR was done against the dev branch, not master.
• My code follows the code style of this project.
• [] My change includes a change to the documentation, if required.
• [] My change adds tests as appropriate.
• I have read and agree to the CONTRIBUTING document.

[Grazfather]

Good find.

[Grazfather]

Have you confirmed that gdb.selected_frame(), if called more than once, returns the same object?

[borismol]

Thank you for review. Unfortunately, no. It changes.
Maybe just remove lru_cache for get_register in such case?

[Grazfather]

That would slow things down a lot. Maybe we can use gdb.selected_frame().pc()? Although that could break on recursive functions. We should play with the frame object to see if there something we can use.

[hugsy]

The bug is confirmed and can be reproduced as such

void f10(){ __asm__("int3"); }
void f9(){ f10(); }
void f8(){ f9(); }
void f7(){ f8(); }
void f6(){ f7(); }
void f5(){ f6(); }
void f4(){ f5(); }
void f3(){ f4(); }
void f2(){ f3(); }
void f1(){ f2(); }
void main(){ f1(); }

Using the following command

gdb -ex run -ex 'frame 5' -ex reg -ex 'pi print(get_register.cache_info())' -ex reg -ex 'pi print(get_register.cache_info())' ./nested.out

I get

• without patch

0:000 ➤  pi print(get_register.cache_info())
CacheInfo(hits=184, misses=26, maxsize=128, currsize=26)
[...]
CacheInfo(hits=191, misses=26, maxsize=128, currsize=26)

• with patch

CacheInfo(hits=184, misses=26, maxsize=128, currsize=26)
[...]
CacheInfo(hits=191, misses=26, maxsize=128, currsize=26)

To the exception that now the context code pane is properly filled. Thanks for the PR @borismol