runtime/cgo: improve Error Handling in `gcc_stack_unix.c` with Assertions

[froz42]

Description

The pthread function calls in gcc_stack_unix.c currently do not check return values, which may lead to silent failures in stack attribute retrieval. This issue proposes adding assert() statements to validate these function calls, ensuring that failures are detected early during development.

Affected File

• src/runtime/cgo/gcc_stack_unix.c

Proposed Solution

• Include <assert.h> to use assert().
• Wrap the following function calls with assert() to verify their return values:
  • pthread_attr_init
  • pthread_getattr_np
  • pthread_attr_get_np
  • pthread_attr_getstack
• This ensures that the program fails fast in case of errors instead of continuing with invalid data.

Rationale

• Improves debugging by catching errors early.
• Prevents undefined behavior due to uninitialized or incorrect stack attributes.

Steps to Reproduce

1. Run the existing code with a failing pthread_attr_init or related function.
2. Observe that errors might not be immediately visible without proper checks.

Expected Behavior

• The program should assert when pthread functions fail, providing clear debugging information.

[gopherbot]

Change https://go.dev/cl/651756 mentions this issue: runtime/cgo: add assertions for safe stack retrieval on unix

[seankhliao]

this doesn't look like a bug report?

[froz42]

Sorry @seankhliao I made a mistake while copying and pasting my edited MR to fix the requirements for the Gopher Robot. I fixed it now