Merge 'git://github.com/Celelibi/syslinux.git/fix/bios/tail-call-stack-overflows'

FIXME: this circumvents some of the issue but is not the cleanest and may
	reoccur.

3 files changed, 80 insertions, 10 deletions

diff --git a/com32/elflink/ldlinux/execute.c b/com32/elflink/ldlinux/execute.c
index 653c880d..39555715 100644
--- a/com32/elflink/ldlinux/execute.c
+++ b/com32/elflink/ldlinux/execute.c
@@ -44,6 +44,7 @@ const struct image_types image_boot_types[] = {
     { NULL, 0 },
 };
 
+extern jmp_buf __return_to_command_prompt;
 extern int create_args_and_load(char *);
 
 __export void execute(const char *cmdline, uint32_t type, bool sysappend)
@@ -136,7 +137,8 @@ __export void execute(const char *cmdline, uint32_t type, bool sysappend)
 		/* Restore the console */
 		ldlinux_console_init();
 
-		ldlinux_enter_command();
+		/* Jump back to the main to call ldlinux_enter_command */
+		longjmp(__return_to_command_prompt, 1);
 	} else if (type == IMAGE_TYPE_CONFIG) {
 		char *argv[] = { LDLINUX, NULL, NULL };
 		char *config;
diff --git a/com32/elflink/ldlinux/ldlinux.c b/com32/elflink/ldlinux/ldlinux.c
index 9b01dd3a..0172117b 100644
--- a/com32/elflink/ldlinux/ldlinux.c
+++ b/com32/elflink/ldlinux/ldlinux.c
@@ -31,6 +31,8 @@ static const struct file_ext file_extensions[] = {
 	{ NULL, 0 },
 };
 
+jmp_buf __return_to_command_prompt;
+
 /*
  * Return a pointer to one byte after the last character of the
  * command.
@@ -302,6 +304,7 @@ __export int main(int argc __unused, char **argv)
 	const void *adv;
 	const char *cmdline;
 	size_t count = 0;
+	int retval;
 
 	ldlinux_console_init();
 
@@ -333,16 +336,25 @@ __export int main(int argc __unused, char **argv)
 		if (!syslinux_setadv(ADV_BOOTONCE, 0, NULL))
 			syslinux_adv_write();
 
-		load_kernel(cmdline); /* Shouldn't return */
-		ldlinux_enter_command();
-	}
-
-	if (!forceprompt && !shift_is_held())
-		ldlinux_auto_boot();
+		/*
+		 * The corresponding longjmp is located in the execute function
+		 * after a COM32 module has returned.
+		 */
+		retval = setjmp(__return_to_command_prompt);
+		if (retval == 0)
+			load_kernel(cmdline); /* Shouldn't return */
+	} else {
+		retval = setjmp(__return_to_command_prompt);
+		if (retval == 0) {
+			if (!forceprompt && !shift_is_held())
+				ldlinux_auto_boot();
 
-	if (defaultlevel > 1)
-		ldlinux_auto_boot();
+			if (defaultlevel > 1)
+				ldlinux_auto_boot();
+		}
+	}
 
+	retval = setjmp(__return_to_command_prompt);
 	ldlinux_enter_command();
 	return 0;
 }
diff --git a/core/elflink/load_env32.c b/core/elflink/load_env32.c
index 492cc095..db19c7aa 100644
--- a/core/elflink/load_env32.c
+++ b/core/elflink/load_env32.c
@@ -55,7 +55,7 @@ void init_module_subsystem(struct elf_module *module)
     list_add(&module->list, &modules_head);
 }
 
-__export int start_ldlinux(int argc, char **argv)
+static int _start_ldlinux(int argc, char **argv)
 {
 	int rv;
 
@@ -96,6 +96,62 @@ again:
 	return rv;
 }
 
+__export int start_ldlinux(int argc, char **argv)
+{
+	/* These variables are static to survive the longjmp. */
+	static int has_jmpbuf = 0;
+	static jmp_buf restart;
+	static int savedargc;
+	static char *heapargs;
+	static size_t argsmem = 0;
+	char **stackargv;
+	char *stackargs;
+	char *p, *q;
+	int i;
+
+
+	/* 1. Save the arguments on the heap */
+	for (i = 0; i < argc; i++)
+		argsmem += strlen(argv[i]) + 1;
+
+	savedargc = argc;
+	heapargs = malloc(argsmem);
+
+	p = heapargs;
+	for (i = 0; i < savedargc; i++) {
+		q = argv[i];
+		while (*q)
+			*p++ = *q++;
+
+		*p++ = '\0';
+	}
+
+	/* 2. Undo the stack if we're restarting ldlinux */
+	if (has_jmpbuf)
+		longjmp(restart, 1);
+
+	setjmp(restart);
+	has_jmpbuf = 1;
+
+	/* 3. Convert the heap memory to stack memory to avoid memory leaks */
+	stackargs = alloca(argsmem);
+	stackargv = alloca(savedargc * (sizeof(char *) + 1));
+
+	memcpy(stackargs, heapargs, argsmem);
+
+	p = stackargs;
+	for (i = 0; i < savedargc; i++) {
+		stackargv[i] = p;
+		p += strlen(p) + 1;
+	}
+
+	stackargv[savedargc] = NULL;
+
+	free(heapargs);
+
+	return _start_ldlinux(savedargc, stackargv);
+}
+
 /* note to self: do _*NOT*_ use static key word on this function */
 void load_env32(com32sys_t * regs __unused)
 {