From e90998302682c41df4813da1ae019c8db79775f5 Mon Sep 17 00:00:00 2001 From: Thomas Meyer Date: Thu, 6 Jul 2017 00:34:05 +0200 Subject: [PATCH] um: Add kerneldoc for userspace_tramp() and start_userspace() Also use correct function name spelling (stub_segv_handler) for better grepping Signed-off-by: Thomas Meyer Signed-off-by: Richard Weinberger --- arch/um/os-Linux/skas/process.c | 31 ++++++++++++++++++++++++++++++- 1 file changed, 30 insertions(+), 1 deletion(-) diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c index 31c9be2c2bdd..819d68656673 100644 --- a/arch/um/os-Linux/skas/process.c +++ b/arch/um/os-Linux/skas/process.c @@ -108,7 +108,7 @@ static void get_skas_faultinfo(int pid, struct faultinfo *fi) wait_stub_done(pid); /* - * faultinfo is prepared by the stub-segv-handler at start of + * faultinfo is prepared by the stub_segv_handler at start of * the stub stack page. We just have to copy it. */ memcpy(fi, (void *)current_stub_stack(), sizeof(*fi)); @@ -175,6 +175,21 @@ static void handle_trap(int pid, struct uml_pt_regs *regs, extern char __syscall_stub_start[]; +/** + * userspace_tramp() - userspace trampoline + * @stack: pointer to the new userspace stack page, can be NULL, if? FIXME: + * + * The userspace trampoline is used to setup a new userspace process in start_userspace() after it was clone()'ed. + * This function will run on a temporary stack page. + * It ptrace()'es itself, then + * Two pages are mapped into the userspace address space: + * - STUB_CODE (with EXEC), which contains the skas stub code + * - STUB_DATA (with R/W), which contains a data page that is used to transfer certain data between the UML userspace process and the UML kernel. + * Also for the userspace process a SIGSEGV handler is installed to catch pagefaults in the userspace process. + * And last the process stops itself to give control to the UML kernel for this userspace process. + * + * Return: Always zero, otherwise the current userspace process is ended with non null exit() call + */ static int userspace_tramp(void *stack) { void *addr; @@ -236,12 +251,24 @@ static int userspace_tramp(void *stack) int userspace_pid[NR_CPUS]; +/** + * start_userspace() - prepare a new userspace process + * @stub_stack: pointer to the stub stack. Can be NULL, if? FIXME: + * + * Setups a new temporary stack page that is used while userspace_tramp() runs + * Clones the kernel process into a new userspace process, with FDs only. + * + * Return: When positive: the process id of the new userspace process, + * when negative: an error number. + * FIXME: can PIDs become negative?! + */ int start_userspace(unsigned long stub_stack) { void *stack; unsigned long sp; int pid, status, n, flags, err; + /* setup a temporary stack page */ stack = mmap(NULL, UM_KERN_PAGE_SIZE, PROT_READ | PROT_WRITE | PROT_EXEC, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); @@ -252,10 +279,12 @@ int start_userspace(unsigned long stub_stack) return err; } + /* set stack pointer to the end of the stack page, so it can grow downwards */ sp = (unsigned long) stack + UM_KERN_PAGE_SIZE - sizeof(void *); flags = CLONE_FILES | SIGCHLD; + /* clone into new userspace process */ pid = clone(userspace_tramp, (void *) sp, flags, (void *) stub_stack); if (pid < 0) { err = -errno;