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util, pasta: Add do_clone() wrapper around __clone2() and clone()

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Spotted in Debian's buildd logs: on ia64, clone(2) is not available:
the glibc wrapper is named __clone2() and it takes, additionally,
the size of the stack area passed by the caller.

Add a do_clone() wrapper handling the different cases, and also
taking care of pointing the child's stack in the middle of the
allocated area: on PA-RISC (hppa), handled by clone(), the stack
grows up, and on ia64 the stack grows down, but the register backing
store grows up -- and I think it might be actually used here.

Suggested-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
Stefano Brivio 2022-11-13 02:21:47 +01:00
parent 7d8c2fb916
commit ab6f825889
3 changed files with 31 additions and 8 deletions
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10
pasta.c
View File

@ -226,11 +226,11 @@ void pasta_start_ns(struct ctx *c, uid_t uid, gid_t gid,
arg.argv = sh_argv;
}
pasta_child_pid = clone(pasta_spawn_cmd,
ns_fn_stack + sizeof(ns_fn_stack) / 2,
CLONE_NEWIPC | CLONE_NEWPID | CLONE_NEWNET |
CLONE_NEWUTS,
(void *)&arg);
pasta_child_pid = do_clone(pasta_spawn_cmd, ns_fn_stack,
sizeof(ns_fn_stack),
CLONE_NEWIPC | CLONE_NEWPID | CLONE_NEWNET |
CLONE_NEWUTS,
(void *)&arg);
if (pasta_child_pid == -1) {
perror("clone");

21
util.c
View File

@ -482,3 +482,24 @@ int write_file(const char *path, const char *buf)
close(fd);
return len == 0 ? 0 : -1;
}
/**
* do_clone() - Wrapper of __clone2() for ia64, clone() for other architectures
* @fn: Entry point for child
* @stack_area: Stack area for child: we'll point callees to the middle of it
* @stack_size: Total size of stack area, passed to callee divided by two
* @flags: clone() system call flags
* @arg: Argument to @fn
*
* Return: thread ID of child, -1 on failure
*/
int do_clone(int (*fn)(void *), char *stack_area, size_t stack_size, int flags,
void *arg)
{
#ifdef __ia64__
return __clone2(fn, stack_area + stack_size / 2, stack_size / 2,
flags, arg);
#else
return clone(fn, stack_area + stack_size / 2, flags, arg);
#endif
}

8
util.h
View File

@ -81,13 +81,15 @@
(((struct in_addr *)(a))->s_addr == ((struct in_addr *)b)->s_addr)
#define NS_FN_STACK_SIZE (RLIMIT_STACK_VAL * 1024 / 8)
int do_clone(int (*fn)(void *), char *stack_area, size_t stack_size, int flags,
void *arg);
#define NS_CALL(fn, arg) \
do { \
char ns_fn_stack[NS_FN_STACK_SIZE]; \
\
clone((fn), ns_fn_stack + sizeof(ns_fn_stack) / 2, \
CLONE_VM | CLONE_VFORK | CLONE_FILES | SIGCHLD, \
(void *)(arg)); \
do_clone((fn), ns_fn_stack, sizeof(ns_fn_stack), \
CLONE_VM | CLONE_VFORK | CLONE_FILES | SIGCHLD,\
(void *)(arg)); \
} while (0)
#if __BYTE_ORDER == __BIG_ENDIAN