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[PATCH] uml: fix TT mode by reverting "use fork instead of clone"
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With Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>

Revert the following patch, because of miscompilation problems in different
environments leading to UML not working *at all* in TT mode; it was merged
lately in 2.6 development cycle, a little after being written, and has
caused problems to lots of people; I know it's a bit too long, but it
shouldn't have been merged in first place, so I still apply for inclusion
in the -stable tree.  Anyone using this feature currently is either using
some older kernel (some reports even used 2.6.12-rc4-mm2) or using this
patch, as included in my -bs patchset.

For now there's not yet a fix for this patch, so for now the best thing is
to drop it (which was widely reported to give a working kernel, and as such
was even merged in -stable tree).

"Convert the boot-time host ptrace testing from clone to fork.  They were
essentially doing fork anyway.  This cleans up the code a bit, and makes
valgrind a bit happier about grinding it."

URL:
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=98fdffccea6cc3fe9dba32c0fcc310bcb5d71529

Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Jeff Dike authored and Linus Torvalds committed Jul 29, 2005
1 parent 2ca3310 commit b85e968
Showing 1 changed file with 29 additions and 19 deletions.
48 changes: 29 additions & 19 deletions arch/um/kernel/process.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -131,7 +131,7 @@ int start_fork_tramp(void *thread_arg, unsigned long temp_stack,
return(arg.pid);
}

static int ptrace_child(void)
static int ptrace_child(void *arg)
{
int ret;
int pid = os_getpid(), ppid = getppid();
Expand Down Expand Up @@ -160,36 +160,41 @@ static int ptrace_child(void)
_exit(ret);
}

static int start_ptraced_child(void)
static int start_ptraced_child(void **stack_out)
{
void *stack;
unsigned long sp;
int pid, n, status;

pid = fork();
if(pid == 0)
ptrace_child();

stack = mmap(NULL, PAGE_SIZE, PROT_READ | PROT_WRITE | PROT_EXEC,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if(stack == MAP_FAILED)
panic("check_ptrace : mmap failed, errno = %d", errno);
sp = (unsigned long) stack + PAGE_SIZE - sizeof(void *);
pid = clone(ptrace_child, (void *) sp, SIGCHLD, NULL);
if(pid < 0)
panic("check_ptrace : fork failed, errno = %d", errno);
panic("check_ptrace : clone failed, errno = %d", errno);
CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
if(n < 0)
panic("check_ptrace : wait failed, errno = %d", errno);
if(!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP))
panic("check_ptrace : expected SIGSTOP, got status = %d",
status);

*stack_out = stack;
return(pid);
}

/* When testing for SYSEMU support, if it is one of the broken versions, we must
* just avoid using sysemu, not panic, but only if SYSEMU features are broken.
* So only for SYSEMU features we test mustpanic, while normal host features
* must work anyway!*/
static int stop_ptraced_child(int pid, int exitcode, int mustexit)
static int stop_ptraced_child(int pid, void *stack, int exitcode, int mustpanic)
{
int status, n, ret = 0;

if(ptrace(PTRACE_CONT, pid, 0, 0) < 0)
panic("stop_ptraced_child : ptrace failed, errno = %d", errno);
panic("check_ptrace : ptrace failed, errno = %d", errno);
CATCH_EINTR(n = waitpid(pid, &status, 0));
if(!WIFEXITED(status) || (WEXITSTATUS(status) != exitcode)) {
int exit_with = WEXITSTATUS(status);
Expand All @@ -200,13 +205,15 @@ static int stop_ptraced_child(int pid, int exitcode, int mustexit)
printk("check_ptrace : child exited with exitcode %d, while "
"expecting %d; status 0x%x", exit_with,
exitcode, status);
if (mustexit)
if (mustpanic)
panic("\n");
else
printk("\n");
ret = -1;
}

if(munmap(stack, PAGE_SIZE) < 0)
panic("check_ptrace : munmap failed, errno = %d", errno);
return ret;
}

Expand Down Expand Up @@ -242,11 +249,12 @@ __uml_setup("nosysemu", nosysemu_cmd_param,

static void __init check_sysemu(void)
{
void *stack;
int pid, syscall, n, status, count=0;

printk("Checking syscall emulation patch for ptrace...");
sysemu_supported = 0;
pid = start_ptraced_child();
pid = start_ptraced_child(&stack);

if(ptrace(PTRACE_SYSEMU, pid, 0, 0) < 0)
goto fail;
Expand All @@ -264,15 +272,15 @@ static void __init check_sysemu(void)
panic("check_sysemu : failed to modify system "
"call return, errno = %d", errno);

if (stop_ptraced_child(pid, 0, 0) < 0)
if (stop_ptraced_child(pid, stack, 0, 0) < 0)
goto fail_stopped;

sysemu_supported = 1;
printk("OK\n");
set_using_sysemu(!force_sysemu_disabled);

printk("Checking advanced syscall emulation patch for ptrace...");
pid = start_ptraced_child();
pid = start_ptraced_child(&stack);
while(1){
count++;
if(ptrace(PTRACE_SYSEMU_SINGLESTEP, pid, 0, 0) < 0)
Expand All @@ -297,7 +305,7 @@ static void __init check_sysemu(void)
break;
}
}
if (stop_ptraced_child(pid, 0, 0) < 0)
if (stop_ptraced_child(pid, stack, 0, 0) < 0)
goto fail_stopped;

sysemu_supported = 2;
Expand All @@ -308,17 +316,18 @@ static void __init check_sysemu(void)
return;

fail:
stop_ptraced_child(pid, 1, 0);
stop_ptraced_child(pid, stack, 1, 0);
fail_stopped:
printk("missing\n");
}

void __init check_ptrace(void)
{
void *stack;
int pid, syscall, n, status;

printk("Checking that ptrace can change system call numbers...");
pid = start_ptraced_child();
pid = start_ptraced_child(&stack);

if (ptrace(PTRACE_OLDSETOPTIONS, pid, 0, (void *)PTRACE_O_TRACESYSGOOD) < 0)
panic("check_ptrace: PTRACE_SETOPTIONS failed, errno = %d", errno);
Expand All @@ -345,7 +354,7 @@ void __init check_ptrace(void)
break;
}
}
stop_ptraced_child(pid, 0, 1);
stop_ptraced_child(pid, stack, 0, 1);
printk("OK\n");
check_sysemu();
}
Expand Down Expand Up @@ -380,10 +389,11 @@ extern void *__syscall_stub_start, __syscall_stub_end;
static inline void check_skas3_ptrace_support(void)
{
struct ptrace_faultinfo fi;
void *stack;
int pid, n;

printf("Checking for the skas3 patch in the host...");
pid = start_ptraced_child();
pid = start_ptraced_child(&stack);

n = ptrace(PTRACE_FAULTINFO, pid, 0, &fi);
if (n < 0) {
Expand All @@ -402,7 +412,7 @@ static inline void check_skas3_ptrace_support(void)
}

init_registers(pid);
stop_ptraced_child(pid, 1, 1);
stop_ptraced_child(pid, stack, 1, 1);
}

int can_do_skas(void)
Expand Down

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