nooc

commit 1b9c7a585b1582ada961616e325af351d0150559
Author: Nihal Jere <nihal@nihaljere.xyz>
Date:   Sat, 30 Oct 2021 22:15:10 -0500

return code generator

Diffstat:
A
main.c
 | 
97
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

1 file changed, 97 insertions(+), 0 deletions(-)
diff --git a/main.c b/main.c
@@ -0,0 +1,97 @@
+#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <elf.h>
+
+char code[] = {0xb8, 60, 0x00, 0x00, 0x00, 0xbf, 0x00, 0x00, 0x00, 0x00, 0xf, 0x5};
+
+int
+elf(char *text, size_t len, FILE *f)
+{
+	Elf64_Ehdr ehdr = { 0 };
+	Elf64_Phdr phdr_text = { 0 };
+	Elf64_Shdr shdr_text = { 0 };
+
+	ehdr.e_ident[0] = ELFMAG0;
+	ehdr.e_ident[1] = ELFMAG1;
+	ehdr.e_ident[2] = ELFMAG2;
+	ehdr.e_ident[3] = ELFMAG3;
+	ehdr.e_ident[4] = ELFCLASS64;
+	ehdr.e_ident[5] = ELFDATA2LSB;
+	ehdr.e_ident[6] = EV_CURRENT;
+	ehdr.e_ident[7] = ELFOSABI_LINUX;
+
+	ehdr.e_type = ET_EXEC;
+	ehdr.e_machine = EM_X86_64;
+	ehdr.e_version = EV_CURRENT;
+
+	ehdr.e_entry = 0x1000;
+	ehdr.e_phoff = sizeof(ehdr);
+	ehdr.e_phentsize = sizeof(phdr_text);
+	ehdr.e_phnum = 1;
+
+	ehdr.e_shoff = sizeof(ehdr) + sizeof(phdr_text);
+	ehdr.e_shentsize = sizeof(shdr_text);
+	ehdr.e_shnum = 1;
+	ehdr.e_ehsize = sizeof(ehdr);
+
+	size_t pretextlen = sizeof(ehdr) + sizeof(phdr_text) + sizeof(shdr_text);
+
+	phdr_text.p_type = PT_LOAD;
+	phdr_text.p_offset = 0x1000;
+	phdr_text.p_vaddr = 0x1000;
+	phdr_text.p_paddr = 0x1000;
+	phdr_text.p_filesz = len;
+	phdr_text.p_memsz = len;
+	phdr_text.p_flags = PF_R | PF_X;
+	phdr_text.p_align = 0x1000;
+
+	shdr_text.sh_name = 10;
+	shdr_text.sh_type = SHT_PROGBITS;
+	shdr_text.sh_flags = SHF_ALLOC | SHF_EXECINSTR;
+	shdr_text.sh_addr = 0x1000;
+	shdr_text.sh_offset = 0x1000;
+	shdr_text.sh_size = len;
+	shdr_text.sh_addralign = 1;
+
+	fwrite(&ehdr, 1, sizeof(Elf64_Ehdr), f);
+	fwrite(&phdr_text, sizeof(phdr_text), 1, f);
+	fwrite(&shdr_text, sizeof(shdr_text), 1, f);
+	char empty = 0;
+	fprintf(stderr, "pretextlen: %u\n", pretextlen);
+	for (int i = 0; i < 0x1000 - pretextlen; i++) {
+		fwrite(&empty, 1, 1, f);
+	}
+	fwrite(text, 1, len, f);
+}
+
+char inbuf[16];
+
+int main(int argc, char *argv[])
+{
+	if (argc < 3)
+		return 1;
+
+	FILE *in = fopen(argv[1], "r");
+	if (!in) {
+		fprintf(stderr, "couldn't open input\n");
+		return 1;
+	}
+
+	fgets(inbuf, 16, in);
+	fclose(in);
+	long val = strtol(inbuf, NULL, 10);
+
+	code[6] = val;
+
+	FILE *out = fopen(argv[2], "w");
+	if (!out) {
+		fprintf(stderr, "couldn't open output\n");
+		return 1;
+	}
+
+	elf(code, sizeof(code), out);
+	fprintf(stderr, "size: %d\n", sizeof(code));
+
+	fclose(out);
+}