vtgl

Commit: 143a28340bdc4536a904140577c247d99337f731
Parent: 54be90c3fc475444f115e8d5c87f4b743f775c35
Author: Randy Palamar
Date:   Sun,  1 Dec 2024 21:44:39 -0700

cleanup render thread's starting call stack

probably not critical but it aids in debugging and was good for
learning more about naked functions and system v abi

Diffstat:
M
platform_linux_amd64.c
 | 
17
+++++++++++------
M
platform_linux_x11.c
 | 
2
+-

2 files changed, 12 insertions(+), 7 deletions(-)
diff --git a/platform_linux_amd64.c b/platform_linux_amd64.c
@@ -113,17 +113,22 @@ syscall6(i64 n, i64 a1, i64 a2, i64 a3, i64 a4, i64 a5, i64 a6)
 	return result;
 }
 
-/* NOTE: graciously taken from nullprogram (Chris Wellons) */
+/* NOTE: based on code from nullprogram (Chris Wellons) */
 __attribute__((naked))
-static i64 clone_thread(void *stack_base)
+static i64
+new_thread(void *stack_base)
 {
 	asm volatile (
-		"mov  %%rdi, %%rsi\n"    // arg2 = stack
+		"mov  %%rdi,    %%rsi\n" // arg2 = new stack
 		"mov  $0x50F00, %%edi\n" // arg1 = clone flags (VM|FS|FILES|SIGHAND|THREAD|SYSVMEM)
-		"mov  $56, %%eax\n"      // SYS_clone
+		"mov  $56,      %%eax\n" // SYS_clone
 		"syscall\n"
-		"mov  %%rsp, %%rdi\n"    // entry point argument
-		"ret\n"
+		"test %%eax, %%eax\n"    // don't mess with the calling thread's stack
+		"jne  1f\n"
+		"mov  %%rsp, %%rdi\n"
+		"sub  $8,    %%rsp\n"    // place a 0 return branch pointer on the child's stack
+		"push (%%rdi)\n"         // push the entry point back onto the stack for use by ret
+		"1: ret\n"
 		: : : "rax", "rcx", "rsi", "rdi", "r11", "memory"
 	);
 }
diff --git a/platform_linux_x11.c b/platform_linux_x11.c
@@ -405,7 +405,7 @@ main(i32 argc, char *argv[], char *envp[])
 
 	struct stack_base *render_stack = new_stack(KB(256));
 	render_stack->entry             = linux_render_thread_entry;
-	clone_thread(render_stack);
+	new_thread(render_stack);
 
 	{
 		MemoryBlock terminal_memory  = linux_block_alloc(MB(32));