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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 <thomas@m3y3r.de>
Signed-off-by: Richard Weinberger <richard@nod.at>
This commit is contained in:
Thomas Meyer 2017-07-06 00:34:05 +02:00 committed by Richard Weinberger
parent 88af23381a
commit e909983026
1 changed files with 30 additions and 1 deletions
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31
arch/um/os-Linux/skas/process.c
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@ -108,7 +108,7 @@ static void get_skas_faultinfo(int pid, struct faultinfo *fi)
wait_stub_done(pid); 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. * the stub stack page. We just have to copy it.
*/ */
memcpy(fi, (void *)current_stub_stack(), sizeof(*fi)); 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[]; 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) static int userspace_tramp(void *stack)
{ {
void *addr; void *addr;
@ -236,12 +251,24 @@ static int userspace_tramp(void *stack)
int userspace_pid[NR_CPUS]; 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) int start_userspace(unsigned long stub_stack)
{ {
void *stack; void *stack;
unsigned long sp; unsigned long sp;
int pid, status, n, flags, err; int pid, status, n, flags, err;
/* setup a temporary stack page */
stack = mmap(NULL, UM_KERN_PAGE_SIZE, stack = mmap(NULL, UM_KERN_PAGE_SIZE,
PROT_READ | PROT_WRITE | PROT_EXEC, PROT_READ | PROT_WRITE | PROT_EXEC,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
@ -252,10 +279,12 @@ int start_userspace(unsigned long stub_stack)
return err; 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 *); sp = (unsigned long) stack + UM_KERN_PAGE_SIZE - sizeof(void *);
flags = CLONE_FILES | SIGCHLD; flags = CLONE_FILES | SIGCHLD;
/* clone into new userspace process */
pid = clone(userspace_tramp, (void *) sp, flags, (void *) stub_stack); pid = clone(userspace_tramp, (void *) sp, flags, (void *) stub_stack);
if (pid < 0) { if (pid < 0) {
err = -errno; err = -errno;