qemu/util/coroutine-ucontext.c
Gerd Hoffmann 0e39c4aa7e build: try improve handling of clang warnings
This patch disables the pragma diagnostic -Wunused-but-set-variable for
clang in util/coroutine-ucontext.c.

This in turn allows us to remove it from the configure check, so the
CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE will succeed for clang.

With that in place clang builds (linux) will use -Werror by default,
which breaks the build due to warning about unaligned struct members.

Just turning off this warning isn't a good idea as it indicates
portability problems.  So make it a warning again, using
-Wno-error=address-of-packed-member.  That way it doesn't break the
build but still shows up in the logs.

Now clang builds qemu without errors.  Well, almost.  There are some
left in the rdma code.  Leaving that to the rdma people.  All others can
use --disable-rdma to workarounds this.

Cc: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-Id: <20180309135945.20436-1-kraxel@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
2018-03-12 08:59:03 +01:00

242 lines
6.4 KiB
C

/*
* ucontext coroutine initialization code
*
* Copyright (C) 2006 Anthony Liguori <anthony@codemonkey.ws>
* Copyright (C) 2011 Kevin Wolf <kwolf@redhat.com>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.0 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, see <http://www.gnu.org/licenses/>.
*/
/* XXX Is there a nicer way to disable glibc's stack check for longjmp? */
#ifdef _FORTIFY_SOURCE
#undef _FORTIFY_SOURCE
#endif
#include "qemu/osdep.h"
#include <ucontext.h>
#include "qemu-common.h"
#include "qemu/coroutine_int.h"
#ifdef CONFIG_VALGRIND_H
#include <valgrind/valgrind.h>
#endif
#if defined(__SANITIZE_ADDRESS__) || __has_feature(address_sanitizer)
#ifdef CONFIG_ASAN_IFACE_FIBER
#define CONFIG_ASAN 1
#include <sanitizer/asan_interface.h>
#endif
#endif
typedef struct {
Coroutine base;
void *stack;
size_t stack_size;
sigjmp_buf env;
#ifdef CONFIG_VALGRIND_H
unsigned int valgrind_stack_id;
#endif
} CoroutineUContext;
/**
* Per-thread coroutine bookkeeping
*/
static __thread CoroutineUContext leader;
static __thread Coroutine *current;
/*
* va_args to makecontext() must be type 'int', so passing
* the pointer we need may require several int args. This
* union is a quick hack to let us do that
*/
union cc_arg {
void *p;
int i[2];
};
static void finish_switch_fiber(void *fake_stack_save)
{
#ifdef CONFIG_ASAN
const void *bottom_old;
size_t size_old;
__sanitizer_finish_switch_fiber(fake_stack_save, &bottom_old, &size_old);
if (!leader.stack) {
leader.stack = (void *)bottom_old;
leader.stack_size = size_old;
}
#endif
}
static void start_switch_fiber(void **fake_stack_save,
const void *bottom, size_t size)
{
#ifdef CONFIG_ASAN
__sanitizer_start_switch_fiber(fake_stack_save, bottom, size);
#endif
}
static void coroutine_trampoline(int i0, int i1)
{
union cc_arg arg;
CoroutineUContext *self;
Coroutine *co;
void *fake_stack_save = NULL;
finish_switch_fiber(NULL);
arg.i[0] = i0;
arg.i[1] = i1;
self = arg.p;
co = &self->base;
/* Initialize longjmp environment and switch back the caller */
if (!sigsetjmp(self->env, 0)) {
start_switch_fiber(&fake_stack_save,
leader.stack, leader.stack_size);
siglongjmp(*(sigjmp_buf *)co->entry_arg, 1);
}
finish_switch_fiber(fake_stack_save);
while (true) {
co->entry(co->entry_arg);
qemu_coroutine_switch(co, co->caller, COROUTINE_TERMINATE);
}
}
Coroutine *qemu_coroutine_new(void)
{
CoroutineUContext *co;
ucontext_t old_uc, uc;
sigjmp_buf old_env;
union cc_arg arg = {0};
void *fake_stack_save = NULL;
/* The ucontext functions preserve signal masks which incurs a
* system call overhead. sigsetjmp(buf, 0)/siglongjmp() does not
* preserve signal masks but only works on the current stack.
* Since we need a way to create and switch to a new stack, use
* the ucontext functions for that but sigsetjmp()/siglongjmp() for
* everything else.
*/
if (getcontext(&uc) == -1) {
abort();
}
co = g_malloc0(sizeof(*co));
co->stack_size = COROUTINE_STACK_SIZE;
co->stack = qemu_alloc_stack(&co->stack_size);
co->base.entry_arg = &old_env; /* stash away our jmp_buf */
uc.uc_link = &old_uc;
uc.uc_stack.ss_sp = co->stack;
uc.uc_stack.ss_size = co->stack_size;
uc.uc_stack.ss_flags = 0;
#ifdef CONFIG_VALGRIND_H
co->valgrind_stack_id =
VALGRIND_STACK_REGISTER(co->stack, co->stack + co->stack_size);
#endif
arg.p = co;
makecontext(&uc, (void (*)(void))coroutine_trampoline,
2, arg.i[0], arg.i[1]);
/* swapcontext() in, siglongjmp() back out */
if (!sigsetjmp(old_env, 0)) {
start_switch_fiber(&fake_stack_save, co->stack, co->stack_size);
swapcontext(&old_uc, &uc);
}
finish_switch_fiber(fake_stack_save);
return &co->base;
}
#ifdef CONFIG_VALGRIND_H
#if defined(CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE) && !defined(__clang__)
/* Work around an unused variable in the valgrind.h macro... */
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-but-set-variable"
#endif
static inline void valgrind_stack_deregister(CoroutineUContext *co)
{
VALGRIND_STACK_DEREGISTER(co->valgrind_stack_id);
}
#if defined(CONFIG_PRAGMA_DIAGNOSTIC_AVAILABLE) && !defined(__clang__)
#pragma GCC diagnostic pop
#endif
#endif
void qemu_coroutine_delete(Coroutine *co_)
{
CoroutineUContext *co = DO_UPCAST(CoroutineUContext, base, co_);
#ifdef CONFIG_VALGRIND_H
valgrind_stack_deregister(co);
#endif
qemu_free_stack(co->stack, co->stack_size);
g_free(co);
}
/* This function is marked noinline to prevent GCC from inlining it
* into coroutine_trampoline(). If we allow it to do that then it
* hoists the code to get the address of the TLS variable "current"
* out of the while() loop. This is an invalid transformation because
* the sigsetjmp() call may be called when running thread A but
* return in thread B, and so we might be in a different thread
* context each time round the loop.
*/
CoroutineAction __attribute__((noinline))
qemu_coroutine_switch(Coroutine *from_, Coroutine *to_,
CoroutineAction action)
{
CoroutineUContext *from = DO_UPCAST(CoroutineUContext, base, from_);
CoroutineUContext *to = DO_UPCAST(CoroutineUContext, base, to_);
int ret;
void *fake_stack_save = NULL;
current = to_;
ret = sigsetjmp(from->env, 0);
if (ret == 0) {
start_switch_fiber(action == COROUTINE_TERMINATE ?
NULL : &fake_stack_save, to->stack, to->stack_size);
siglongjmp(to->env, action);
}
finish_switch_fiber(fake_stack_save);
return ret;
}
Coroutine *qemu_coroutine_self(void)
{
if (!current) {
current = &leader.base;
}
return current;
}
bool qemu_in_coroutine(void)
{
return current && current->caller;
}