rust-teeny-nostd: compare with asm

README.md

@@ -5,4 +5,4 @@ PoC's showing how rust can do stuff people often critiquize it about.
 # Members
 
 - `rust-teeny`: A rust std binary only **8.0 KiB** big, achieves so by `abort()`ing instead of having graceful error logging, panics shouldn't have any source information nor should there be `Debug` implementations, no debug symbols and any potential path reference to `$PWD` is renamed. It carries a shellcode payload loaded into memory and executed from memory.
-- `rust-teeny-nostd`: Same as avobe but `no_std`, **4.1 KiB**.
+- `rust-teeny-nostd`: Same as avobe but `no_std`, **4.1 KiB**. Can't even get raw assembly as small, rust wins by 16 Bytes, `.text` is the same size but rust beats with dynamic table sections and such.

rust-teeny-nostd/justfile

@@ -2,6 +2,10 @@ alias b := build
 alias s := stat
 alias z := stat-size
 
+alias basm := build-asm
+alias sasm := stat-asm
+alias zasm := stat-size-asm
+
 target := "x86_64-unknown-linux-gnu"
 
 build:
@@ -16,7 +20,7 @@ build:
         -Cpanic=immediate-abort --remap-path-prefix=$PWD=[src] \
     " cargo \
         \
-        -Zbuild-std=core,alloc,std,panic_abort \
+        -Zbuild-std=core,panic_abort \
         -Zbuild-std-features="optimize_for_size" \
         \
         b -r --target {{ target }}
@@ -32,8 +36,18 @@ build:
 
     # Not sure why .gnu.version and .gnu.hash don't break if I remove them in my machine, but that's very relative and its related to dynamic loading, but they could reduce size by `0.2 KiB`
 
+build-asm:
+    clang -Wl,--gc-sections -Wl,--as-needed -Wl,--strip-all -Wl,--build-id=none -s -fuse-ld=lld -Oz same.S -o target/asm
+    strip --strip-all --strip-unneeded -R .comment -R .note.\* -R .eh_frame\* target/asm
+
 stat:
     stat target/{{ target }}/release/rust-teeny
 
+stat-asm:
+    stat target/asm
+
 stat-size:
     stat target/{{ target }}/release/rust-teeny -c "%s" | numfmt --to=iec-i
+
+stat-size-asm:
+    stat target/asm -c "%s" | numfmt --to=iec-i

rust-teeny-nostd/same.S

@@ -0,0 +1,60 @@
+.intel_syntax noprefix
+.globl main
+
+.section .rodata
+SHELLCODE: .ascii "\x31\xC0\xFF\xC0\x89\xC7\x48\x8D\x35\x08\x00\x00\x00\xBA\x0E\x00\x00\x00\x0F\x05\xC3Hello, World!\n"
+SHELLCODE_end:
+
+SHELLCODE_len = SHELLCODE_end - SHELLCODE
+
+#define PROT_READ 0x1
+#define PROT_WRITE 0x2
+#define PROT_EXEC 0x4
+
+#define MAP_PRIVATE 0x2
+#define MAP_ANONYMOUS 0x20
+
+#define MAP_FAILED -1
+
+.section .text
+main:
+    #define VAR1 [rsp]
+    sub rsp, 8
+
+    // rax = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0)
+    xor edi, edi
+    mov rsi, OFFSET SHELLCODE_len
+    mov edx, PROT_READ | PROT_WRITE
+    mov ecx, MAP_PRIVATE | MAP_ANONYMOUS
+    mov r8, -1
+    xor r9d, r9d
+    call QWORD PTR [mmap@GOTPCREL + rip]
+    mov VAR1, rax
+
+    cmp rax, MAP_FAILED
+    je .abort
+
+    // rax = mmove(VAR1, SHELLCODE, SHELLCODE_len)
+    mov rdi, rax
+    lea rsi, [rip+SHELLCODE]
+    mov rdx, OFFSET SHELLCODE_len
+    call QWORD PTR [memmove@GOTPCREL + rip]
+
+    // rax = mprotect(exec_mem, content.len(), PROT_READ | PROT_EXEC)
+    mov rdi, rax
+    mov rsi, OFFSET SHELLCODE_len
+    mov edx, PROT_READ | PROT_EXEC
+    call QWORD PTR [mprotect@GOTPCREL + rip]
+
+    test rax, rax
+    jnz .abort
+
+    mov rax, VAR1
+    call qword ptr VAR1
+
+    // exit(0)
+    xor edi, edi
+    call QWORD PTR [exit@GOTPCREL + rip]
+
+.abort:
+    call QWORD PTR [abort@GOTPCREL + rip]