Modifications Made to glibc and `crt1.c`

1. Changes to glibc

1.1 Changing the System Call Mechanism

The system call mechanism was modified to route system calls through rawposix instead of directly invoking the kernel. The new format for making system calls is structured as follows:

MAKE_SYSCALL(syscallnum, "syscall|callname", arg1, arg2, arg3, arg4, arg5, arg6)

For each system call file in glibc, a header file named syscall-template.h was added with the following content:

#include <sys/syscall.h>
#include <stdint.h>    // For uint64_t
#include <unistd.h>
#include <lind_syscall.h>

// Define NOTUSED for unused arguments
#define NOTUSED 0xdeadbeefdeadbeefULL

// Macro to create a syscall and redirect it to rawposix
#define MAKE_SYSCALL(syscallnum, callname, arg1, arg2, arg3, arg4, arg5, arg6) \
    lind_syscall(syscallnum, \
                 (unsigned long long)(callname), \
                 (unsigned long long)(arg1), \
                 (unsigned long long)(arg2), \
                 (unsigned long long)(arg3), \
                 (unsigned long long)(arg4), \
                 (unsigned long long)(arg5), \
                 (unsigned long long)(arg6))

The MAKE_SYSCALL macro redirects system calls to rawposix, providing an interface for syscall handling in this context.

1.2 Eliminating Assembly Code

Since WebAssembly (WASM) does not support assembly, all assembly-related components in glibc were removed: - Inline assembly code was rewritten in C. - Files ending in .s were converted to .c files, and their functionalities were reimplemented in C.

1.3 Handling Automatically Generated `.s` Files

glibc automatically generates .s files for certain system calls. To address this: - The script responsible for generating these .s files was disabled. - The corresponding system calls were manually implemented in C and placed in appropriate .c files.

1.4 Additional Modifications

Disable _dl_mcount_wrapper_check: This functionality was disabled as it is not required in the WASI environment.
Change initial-exec to local-exec: All instances of initial-exec were replaced with local-exec to align with WebAssembly's threading and memory model.
Implement BYTE_COPY_FWD and BYTE_COPY_BWD: These functions were implemented in C without relying on memcpy or memmove to ensure compatibility with the WASM environment.
Disable attribute_relro: The original C code places the vtable into the relro section in the binary. Since WebAssembly binaries do not have this section, the attribute was disabled.

2. Modifications and Additions to `crt1.c` for WASI

2.1 WASI-Specific Function Wrappers

Wrappers for WASI Snapshot Preview 1 APIs: Several wrappers were defined for handling WASI args and environ APIs, including:
__imported_wasi_snapshot_preview1_args_sizes_get
__imported_wasi_snapshot_preview1_args_get
__imported_wasi_snapshot_preview1_environ_get
__imported_wasi_snapshot_preview1_environ_sizes_get
Implementation: These wrappers use the following attribute for integration: c __attribute__(( __import_module__("wasi_snapshot_preview1"), __import_name__("function_name") ));
Purpose: Enables access to WASI-specific argument and environment APIs.

2.2 Environment Initialization

Added __wasi_initialize_environ: This function initializes the environment variables by:
Using __wasi_environ_sizes_get to determine the size of environment data.
Using __wasi_environ_get to populate the environ array.
Fallback Logic: If the environment is empty, the program:
Falls back to a static empty environment (empty_environ).
Exits with an appropriate error code when necessary.

2.3 Thread and TLS Setup

Added Calls to __libc_setup_tls and __wasi_init_tp: These functions are included in _start to set up thread-local storage (TLS) and thread pointers, which are essential for multithreading or TLS-dependent code.

2.4 Main Function Handling

Modified __main_void to Handle WASI Arguments:
Initializes command-line arguments by:
- Using __wasi_args_sizes_get to determine argument buffer sizes.
- Using __wasi_args_get to populate argv and argv_buf.
Passes the initialized arguments to __main_argc_argv.
Weak Symbol for __main_argc_argv: Defined as a weak symbol to allow the dynamic linker to handle cases where no main function exists (e.g., in reactor-style applications).

2.5 Error Handling

Specific Exit Codes:
Introduced _Exit(EX_OSERR) and _Exit(EX_SOFTWARE) for different error scenarios, aligning with sysexits.h standards.
Purpose: Provides descriptive and standard error handling for memory allocation or initialization failures.

2.6 Placeholder Functions

Added Stub for __wasm_call_dtors:
An empty placeholder function for future destructor handling.
Added Stub for __wasi_proc_exit:
A placeholder function for handling process exits in WASI.

2.7 Memory Allocation for `argv` and `environ`

Allocates memory dynamically for:
Argument buffers (argv_buf) and pointers (argv).
Environment buffers (environ_buf) and pointers (environ_ptrs).
Uses malloc and calloc with robust error handling to prevent memory allocation failures.

Modifications Made to glibc and crt1.c