This is possible and most easily done using OBJCOPY found in BINUTILS. You effectively take the data file as binary input and then output it to an object file format that can be linked to your program. OBJCOPY will even produce a start and end symbol as well as the size of the data area … Read more
The code must be in a page with execute permission. By default, stack and read-write static data (like non-const globals) are in pages mapped without exec permission, for security reasons. The simplest way is to compile with gcc -z execstack, which links your program such that stack and global variables (static storage) get mapped in … Read more
The problem is with your stack usage. First, the ABI docs mandate rsp be 16 byte aligned before a call. Since a call will push an 8 byte return address on the stack, you need to adjust rsp by a multiple of 16 plus 8 to get back to 16-byte alignment. The 16 * n … Read more
NASM 2.11.08 and 2.13.02+ have bugs with macho64 output. What you are observing seems to be something I saw specifically with 2.13.02+ recently when using absolute references. The final linked program has incorrect fixups applied so the reference to str2 is incorrect. The incorrect fixup causes us to print out memory that isn’t str2. NASM … Read more
You can’t ret from start; it isn’t a function and there’s no return address on the stack. The stack pointer points at argc on process entry. As n.m. said in the comments, the issue is that you aren’t exiting the program, so execution runs off into garbage code and you get a segfault. What you … Read more
If you tell the assembler to assemble arbitrary bytes somewhere, it will. db is a pseudo-instruction that emits bytes, so mov eax, 60 and db 0xb8, 0x3c, 0, 0, 0 are exactly equivalent as far as NASM is concerned. Either one will emit those 5 bytes into the output at the current position. If you … Read more
NASM answer, MASM is totally different One of the answers on the linked question has a quote from the NASM manual’s examples which does answer your question. As requested, I’ll expand on it for all three cases (and correct the lower-case vs. upper-case ASCII encoding error!): db ‘ABCDE’ ; 0x41 0x42 0x43 0x44 0x45 (5 … Read more
Related: WSL2 does allow 32-bit user-space programs, WSL1 doesn’t. See Does WSL 2 really support 32 bit program? re: making sure you’re actually using WSL2. The rest of this answer was written before WLS2 existed. The issue is with Ubuntu for Windows (Windows Subsystem for Linux version 1). It only supports the 64-bit syscall interface … Read more
From man 2 write, you can see the signature of write is, ssize_t write(int fd, const void *buf, size_t count); It takes a pointer (const void *buf) to a buffer in memory. You can’t pass it a char by value, so you have to store it to memory and pass a pointer. (Don’t print one … Read more
Your first code (leading to the title question) is buggy because it overwrites the rdtsc and rdtscp results with the cpuid results in EAX,EBX,ECX and EDX. Use lfence instead of cpuid; on Intel since forever and AMD with Spectre mitigation enabled, lfence will serialize the instruction stream and thus do what you want with rdtsc. … Read more