Thomas,
Am 09.05.2017 um 10:15 schrieb Thomas Meyer:
> attached patch work correctly under Linux. But no change under WSL. As stated
> in the relevant GH issue, there seems to be far more road blockers to make
> UML work under WSL.
>
> With you patch I get under WSL:
>
> thomas@DESKTOP-DQBDJ0U:/mnt/c/Users/thomas/VmShare$ ./linux
> Core dump limits :
> soft - NONE
> hard - NONE
> Checking that ptrace can change system call numbers...check_ptrace : failed
> to modify system call: Invalid Argument
Okay, now it fails later.
UML needs to cancel syscalls on the host side, it does so by turning them into
a getpid() which has no side
effects and, on non-ancient systems, by using PTRACE_SYSEMU.
Let's figure whether they support PTRACE_SYSEMU, can you test the attached
patch?
Also please test segv1.c, it tests whether WSL allows us to handle page faults
in userspace.
It should output this:
SIGSEGV at 0xdeadbeef, fixing up
x=3, &x=0xdeadbeef
IOW we write to 0xdeadbeef, catch the fault and fix it.
Thanks,
//richard
diff --git a/arch/um/os-Linux/start_up.c b/arch/um/os-Linux/start_up.c
index 22a358ef1b0c..37c42cead79d 100644
--- a/arch/um/os-Linux/start_up.c
+++ b/arch/um/os-Linux/start_up.c
@@ -259,7 +259,7 @@ static void __init check_sysemu(void)
static void __init check_ptrace(void)
{
int pid, syscall, n, status;
-
+#if 0
non_fatal("Checking that ptrace can change system call numbers...");
pid = start_ptraced_child();
@@ -293,6 +293,7 @@ static void __init check_ptrace(void)
}
stop_ptraced_child(pid, 0, 1);
non_fatal("OK\n");
+#endif
check_sysemu();
}
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/ucontext.h>
#include <signal.h>
#include <errno.h>
static void segv(int sig, siginfo_t *info, void *context)
{
ucontext_t *c = context;
mcontext_t m = c->uc_mcontext;
void *fault_addr = (void *)m.gregs[REG_CR2];
void *addr;
printf("SIGSEGV at 0x%lx, fixing up\n", (unsigned long)fault_addr);
addr = mmap(fault_addr, 4096, PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_PRIVATE, 0, 0);
if (addr == MAP_FAILED) {
printf("map failed!\n");
exit(1);
}
}
static void install_handler(void)
{
struct sigaction sa;
sa.sa_sigaction = segv;
sa.sa_flags = SA_SIGINFO;
sigaction(SIGSEGV, &sa, NULL);
}
int main(void)
{
int *x = (void *)0xdeadbeef;
install_handler();
*x = 3;
printf("x=%i, &x=%p\n", *x, x);
return 0;
}
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