More info/demo on environment variables

README.md

@@ -116,8 +116,8 @@ let ax = Axecutor.from_binary(/* elf file content as Uint8Array */);
 // and writes the stack pointer to RSP
 ax.init_stack_program_start(
   8n * 1024n, // Stack size
-  ["/bin/my_binary", "arg1", "arg2"],
-  [ /* environment variables */ ]
+  ["/bin/my_binary", "arg1", "arg2"], // argv
+  ["COLORTERM=truecolor", "TERM=xterm-256color" ] // environment variables
 );
 
 

examples/programs/args/args.S

@@ -1,8 +1,11 @@
 .intel_syntax noprefix
 
 .section .rodata
-.Largv: .asciz "argv values:\n"
-.Largv_len: .quad 13
+.Largv: .ascii "--------------------------------------------------\nargv values:\n--------------------------------------------------\n"
+.Largv_len: .quad .Largv_len - .Largv
+
+.Lenvp: .ascii "--------------------------------------------------\nenvp values:\n--------------------------------------------------\n"
+.Lenvp_len: .quad .Lenvp_len - .Lenvp
 
 .Lnewline: .asciz "\n"
 .Lnewline_len: .quad 1
@@ -30,17 +33,7 @@ _start:
 	je .Lend_argv
 
     pop rsi # pointer to string, argv[i]
-	# strlen:
-	xor rax, rax
-	push rbx
-	.Lstrlen_loop:
-		mov bl, [rsi+rax]
-		cmp bl, 0
-		je .Lstrlen_end
-		inc rax
-		jmp .Lstrlen_loop
-	.Lstrlen_end:
-	pop rbx
+	call strlen
 
 	mov rdx, rax # number of bytes to write
 	mov rax, 1 # write system call
@@ -53,6 +46,37 @@ _start:
 	JMP .Lstart_argv
 
 	.Lend_argv:
+
+	# after argv values, we have 8 zero bytes on the stack
+	pop rsi
+
+	# now we can write "envp values:\n"
+	mov rax, 1 # write system call
+	mov rdi, 1 # Stdout
+	lea rsi, [rip+.Lenvp] # pointer to string, argv[i]
+	mov rdx, [rip+.Lenvp_len] # Number of bytes to write
+	syscall
+
+	# envp, just like argv, is a null-terminated array of string pointers
+	# unlike argv, we don't have a count, so we just iterate until we find null
+	.Lstart_envp:
+	pop rsi # pointer to string, envp[i]
+	cmp rsi, 0
+	je .Lend_envp
+
+	call strlen
+
+	mov rdx, rax # number of bytes to write
+	mov rax, 1 # write system call
+	mov rdi, 1 # Stdout
+	# rsi already points to envp[i]
+	syscall
+
+	call newline
+
+	JMP .Lstart_envp
+	.Lend_envp:
+
 	mov rdi, Vargc
     mov rax, 0x3c
     syscall
@@ -80,3 +104,17 @@ newline:
 	pop rax
 
 	ret
+
+# strlen(char *rsi) -> rax
+strlen:
+	xor rax, rax
+	push rbx
+	.Lstrlen_loop:
+		mov bl, [rsi+rax]
+		cmp bl, 0
+		je .Lstrlen_end
+		inc rax
+		jmp .Lstrlen_loop
+	.Lstrlen_end:
+	pop rbx
+	ret

examples/web/src/components/Demo.vue

@@ -8,20 +8,21 @@
     <br />
     <p>
       Please select an ELF binary compiled with <code>-m64 -nostdlib -static</code> that only interacts with std{in,out,err}.
-      Some binaries (especially the ones that use libc) will not work due to the ELF loader being very basic right now.
+      Some binaries, especially the ones that use libc, might not work.
     </p>
     <div>
       <input type="file" ref="file">
       <button @click="runFile">Run!</button>
     </div>
     <br />
     <div v-if="programs.length > 0">
-      You can also load one of the following binaries:
+      Click to load one of the following binaries:
       <ul>
         <li v-for="program in programs" :key="program.name">
-          <a :href="'/programs/' + program.binary" @click.prevent="setBinary(program.binary)">{{ program.name }}</a> (<a :href="program_source_prefix + program.source_name" target="_blank">Source</a>)
+          <a :href="'/programs/' + program.binary" @click.prevent="setBinary(program.binary)">{{ program.name }}</a>: {{ program.description }} (<a :href="program_source_prefix + program.source_name" target="_blank">Source</a>)
         </li>
       </ul>
+      <br />
       You can also download these binaries and run them on Linux. This of course shows that the emulator can run some real binaries without any modifications.
     </div>
     <br />
@@ -58,40 +59,47 @@ export default defineComponent({
     };
 
     const programs = [
+      {
+        name: "Exit Code",
+        binary: "exit_code.bin",
+        source_name: "exit/exit_code.s",
+        description: "Exits with exit code 13",
+      },
       {
         name: "Hello World",
         binary: "hello_world.bin",
         source_name: "hello_world/hello_world.s",
+        description: "Prints \"Hello World!\" to stdout",
       },
       {
         name: "Alphabet",
         binary: "alphabet.bin",
         source_name: "alphabet/alphabet.s",
-      },
-      {
-        name: "Exit Code",
-        binary: "exit_code.bin",
-        source_name: "exit/exit_code.s",
+        description: "Prints the alphabet to stdout",
       },
       {
         name: "Input to uppercase",
         binary: "uppercase_naive.bin",
         source_name: "uppercase/uppercase_naive.s",
+        description: "Repeatedly reads a single character from stdin and prints the uppercase representation",
       },
       {
         name: "Byte to hex",
         binary: "hex_naive.bin",
         source_name: "hex/hex_naive.s",
+        description: "Repeatedly reads a single byte from stdin and prints the hex representation",
       },
       {
         name: "String length",
         binary: "strlen.bin",
         source_name: "strlen/strlen.s",
+        description: "Reads a string from stdin and prints its length",
       },
       {
         name: "Print command-line arguments",
         binary: "args.bin",
         source_name: "args/args.S",
+        description: "Prints all command-line arguments and environment variables",
       },
       /*
       {
@@ -309,7 +317,11 @@ export default defineComponent({
         return;
       }
       try {
-        ax.init_stack_program_start(8n * 1024n, ["/bin/my_binary", "arg1", "arg2"], []);
+        ax.init_stack_program_start(8n * 1024n, ["/bin/my_binary", "arg1", "arg2"], [
+          "USER=demo-user",
+          "COLORTERM=truecolor",
+          "TERM=xterm-256color",
+        ]);
         ax.hook_before_mnemonic(Mnemonic.Syscall, this.syscallHandler);
       }
       catch (e) {