Re: [PATCH 3/7] provide kernel_execve on all architectures

[Ralf Baechle <ralf@linux-mips.org>]

On Sun, Aug 27, 2006 at 11:47:37PM +0200, Arnd Bergmann wrote:

> This adds the new kernel_execve function on all architectures
> that were using _syscall3() to implement execve.
> 
> The implementation uses code from the _syscall3 macros provided
> in the unistd.h header file. I don't have cross-compilers for
> any of these architectures, so the patch is untested with the
> exception of i386.
> 
> Most architectures can probably implement this in a nicer way
> in assembly or by combining it with the sys_execve implementation
> itself, but this should do it for now.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Two bugs in your MIPS version of kernel_execve(); the inline asm which
was copying from _syscall3 macro was still using the #stringify
operation.  It also didn't get the result return in case of errors
right - $a3 = 1 indicates an error in which case $v0 will contain the
positive error number.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

diff --git a/arch/mips/kernel/syscall.c b/arch/mips/kernel/syscall.c
index 0721314..b73b26c 100644
--- a/arch/mips/kernel/syscall.c
+++ b/arch/mips/kernel/syscall.c
@@ -399,3 +399,32 @@ asmlinkage void bad_stack(void)
 {
 	do_exit(SIGSEGV);
 }
+
+/*
+ * Do a system call from kernel instead of calling sys_execve so we
+ * end up with proper pt_regs.
+ */
+int kernel_execve(const char *filename, char *const argv[], char *const envp[])
+{
+	register unsigned long __a0 asm("$4") = (unsigned long) filename;
+	register unsigned long __a1 asm("$5") = (unsigned long) argv;
+	register unsigned long __a2 asm("$6") = (unsigned long) envp;
+	register unsigned long __a3 asm("$7");
+	unsigned long __v0;
+
+	__asm__ volatile ("					\n"
+	"	.set	noreorder				\n"
+	"	li	$2, %5		# __NR_execve		\n"
+	"	syscall						\n"
+	"	move	%0, $2					\n"
+	"	.set	reorder					\n"
+	: "=&r" (__v0), "=r" (__a3)
+	: "r" (__a0), "r" (__a1), "r" (__a2), "i" (__NR_execve)
+	: "$2", "$8", "$9", "$10", "$11", "$12", "$13", "$14", "$15", "$24",
+	  "memory");
+
+	if (__a3 == 0)
+		return __v0;
+
+	return -__v0;
+}