refactor(esp): split _exit into separate file for QEMU support

[luoliwoshang]

Summary

• Move _exit implementation from syscalls.c to syscalls_exit.c
• This separation allows easy replacement with semihosting version for QEMU emulator support
• Enables llgo to compile the semihosting _exit as a separate object file that can override the default implementation

Related

• fix(esp32c3): use semihosting _exit for QEMU emulator support llgo#1539

🤖 Generated with Claude Code

[gemini-code-assist]

Summary of Changes

Hello @luoliwoshang, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refactors the _exit system call implementation by isolating it into its own source file. This strategic move enhances modularity and significantly improves compatibility with the QEMU emulator by allowing alternative _exit versions, such as semihosting, to be easily integrated and override the default behavior during compilation.

Highlights

• _exit implementation refactor: The _exit function's implementation has been moved from syscalls.c to a new, dedicated file named syscalls_exit.c.
• Enhanced QEMU emulator support: This separation allows for the easy replacement of the default _exit implementation with a semihosting version, crucial for QEMU emulator support.
• Improved llgo compilation flexibility: The change enables llgo to compile the semihosting _exit as a separate object file, which can then override the default implementation as needed.

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[gemini-code-assist]

Code Review

This pull request refactors the _exit function by moving it from syscalls.c to a new, separate file syscalls_exit.c. This is a sensible refactoring that improves modularity and will allow the function to be more easily overridden for different build configurations, such as for QEMU support. The change is clear and well-motivated. I have one minor suggestion to improve the code by explicitly marking an unused function parameter.

[luoliwoshang]

@MeteorsLiu

[xgopilot]

IMPORTANT: This function should be marked as __attribute__((weak)) to enable the stated goal of "easy replacement with semihosting version for QEMU emulator support."

Following the pattern in syscalls.c:28 where _write is declared weak, this should be:

Suggested change

	void
	__attribute__((weak))
	void

Without the weak attribute, semihosting implementations cannot override this function, defeating the purpose of this refactoring.

[xgopilot]

CRITICAL: The Makefile.inc was not updated to include the new syscalls_exit.c file. This will cause build failures.

Please add syscalls_exit.c to the build sources in libgloss/riscv/esp/Makefile.inc:

%C%_libsys_board_a_SOURCES = \
	%D%/esp_board.c \
	%D%/syscalls.c \
	%D%/syscalls_exit.c

Without this change, the _exit symbol will be undefined during linking.

[xgopilot]

Code Review Summary

The refactoring concept is sound—separating _exit enables flexible replacement for QEMU semihosting. However, two critical issues must be addressed:

1. Missing Makefile update: Build will fail without adding syscalls_exit.c to sources
2. Missing weak attribute: Function cannot be overridden as intended without __attribute__((weak))

These prevent the PR from achieving its stated goal. Please see inline comments for details.