http://llvm.org/viewvc/llvm-project?rev=182456&view=rev adds a workaround and a better
test.

Full fix may require a significant surgery, so I'd like to see if a simple thing
is enough. 

I've got a test case that gives a false-positive error around swapcontext:

"ERROR: AddressSanitizer: SEGV on unknown address 0x000000000"

When I blacklist the file making that call, the code then prints a warning referring
to this bug:

"WARNING: ASan is ignoring requested __asan_handle_no_return: stack top: . . . 
False positive error reports may follow
For details see http://code.google.com/p/address-sanitizer/issues/detail?id=189"

It's from the test suite of the Charm++ parallel runtime system (http://charmplusplus.org).
If test cases for this would be useful, I'd be happy to help in understanding that
code. If you want it reduced, I can probably do some, but it's a fairly large system
with a lot of cross-dependencies.

Does asan actually report false positives after the warning about swapcontext?
A minimized test is always welcome, but we can not promise that we'll fix it -- 
swapcontext is a really tricky beast. 

Note that it generally makes little sense in blacklisting the code that performs a NULL
dereference.

Here is false positive.

When you destroy a std::exception_ptr allocated from another stack without rethrowing
it, then it crashes.

GCC 4.9.2 (on Gentoo). Boost 1.56.0 compiled with C++11 support.

{{{
==26409==WARNING: ASan is ignoring requested __asan_handle_no_return: stack top: 0x7fff0420b000;
bottom 0x63100000f000; size: 0x1cef041fc000 (31812891951104)
False positive error reports may follow
For details see http://code.google.com/p/address-sanitizer/issues/detail?id=189
=================================================================
==26409==ERROR: AddressSanitizer: stack-buffer-underflow on address 0x6310000104a0
at pc 0x7fd9fccdcde3 bp 0x631000010320 sp 0x63100000fac8
WRITE of size 240 at 0x6310000104a0 thread T0
    #0 0x7fd9fccdcde2 (/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.2/libasan.so.1+0x2fde2)
    #1 0x7fd9fbe8b046 in _Unwind_Resume (/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.2/libgcc_s.so.1+0x10046)
    #2 0x406dc9 in my_coroutine(boost::coroutines::pull_coroutine<std::__exception_ptr::exception_ptr>&)
(/tmp/a.out+0x406dc9)
    #3 0x41e7f4 in boost::coroutines::detail::push_coroutine_object<boost::coroutines::pull_coroutine<std::__exception_ptr::exception_ptr>,
std::__exception_ptr::exception_ptr, void (&)(boost::coroutines::pull_coroutine<std::__exception_ptr::exception_ptr>&),
boost::coroutines::basic_standard_stack_allocator<boost::coroutines::stack_traits>
>::run(std::__exception_ptr::exception_ptr*) (/tmp/a.out+0x41e7f4)
    #4 0x41bb88 in void boost::coroutines::detail::trampoline_push<boost::coroutines::detail::push_coroutine_object<boost::coroutines::pull_coroutine<std::__exception_ptr::exception_ptr>,
std::__exception_ptr::exception_ptr, void (&)(boost::coroutines::pull_coroutine<std::__exception_ptr::exception_ptr>&),
boost::coroutines::basic_standard_stack_allocator<boost::coroutines::stack_traits>
> >(long) (/tmp/a.out+0x41bb88)
    #5 0x7fd9fc89e710 in make_fcontext (/usr/lib64/libboost_context-cxx11-gcc4_9_2.so.1.56.0+0x710)

0x6310000104a0 is located 64672 bytes inside of 65536-byte region [0x631000000800,0x631000010800)
allocated by thread T0 here:
    #0 0x7fd9fcd04787 in malloc (/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.2/libasan.so.1+0x57787)
    #1 0x414890 in boost::coroutines::basic_standard_stack_allocator<boost::coroutines::stack_traits>::allocate(boost::coroutines::stack_context&,
unsigned long) (/tmp/a.out+0x414890)
    #2 0x40d975 in boost::coroutines::push_coroutine<std::__exception_ptr::exception_ptr>::push_coroutine<void
(&)(boost::coroutines::pull_coroutine<std::__exception_ptr::exception_ptr>&)>(void
(&)(boost::coroutines::pull_coroutine<std::__exception_ptr::exception_ptr>&), boost::coroutines::attributes
const&) (/tmp/a.out+0x40d975)
    #3 0x406ecf in main (/tmp/a.out+0x406ecf)
    #4 0x7fd9fbaf8dc4 in __libc_start_main (/lib64/libc.so.6+0x24dc4)
}}}

Adding Project:AddressSanitizer as part of GitHub migration.

nahs-MBP:desktop nah$ clang --version
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin15.2.0
Thread model: posix

#include <setjmp.h>
#include <stdio.h>
#include <string.h>
#include <signal.h>

static jmp_buf return_jump;

static void signal_handler(int sig)
{
    longjmp(return_jump, 1);
}

static void setup_test_sig_handler(void)
{
    struct sigaction sa;
    sigset_t ss;
    unsigned int i;

    for(i = 1; i < 512; i++)
    {
        (void)sigfillset(&ss);
        sa.sa_flags = SA_RESTART;
        sa.sa_handler = signal_handler;
        sa.sa_mask = ss;
        (void)sigaction((int)i, &sa, NULL);
    }

    return;
}

int main(void)
{
    int rtrn = setjmp(return_jump);
    if(rtrn < 0)
    {
        perror("setjmp");
        return (-1);
    }

    setup_test_sig_handler();

    /* Cause signal. */
    memmove(NULL, "123456789", 9);

    return (0);
}

ASAN:SIGSEGV
=================================================================
==8425==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x000105ab39e2 bp 0x7fff5a1ab9a0 sp 0x7fff5a1ab128 T0)
    #0 0x105ab39e1 in __sanitizer::internal_memmove(void*, void const*, unsigned long) (/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/7.0.2/lib/darwin/libclang_rt.asan_osx_dynamic.dylib+0x569e1)
    #1 0x105a54a9e in main (/Users/nah/Desktop/./test+0x100000a9e)
    #2 0x7fff95a7c5ac in start (/usr/lib/system/libdyld.dylib+0x35ac)
    #3 0x0  (<unknown module>)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV ??:0 __sanitizer::internal_memmove(void*, void const*, unsigned long)
==8425==ABORTING
==8425==WARNING: ASan is ignoring requested __asan_handle_no_return: stack top: 0x7fff5a1ac000; bottom 0x000106b5d000; size: 0x7ffe5364f000 (140730297544704)
False positive error reports may follow
For details see http://code.google.com/p/address-sanitizer/issues/detail?id=189
ASAN:SIGSEGV
==8425==AddressSanitizer: while reporting a bug found another one. Ignoring.
`

0x00005555560f49af <+1191>:	je     0x5555560f49d2 <co_switch_context+1226>
   0x00005555560f49b1 <+1193>:	movq   $0x45e0360e,(%rbx)
   0x00005555560f49b8 <+1200>:	movabs $0xf5f5f5f5f5f5f5f5,%rax
   0x00005555560f49c2 <+1210>:	mov    %rax,0x7fff8000(%r14)
   0x00005555560f49c9 <+1217>:	mov    0x38(%rbx),%rax
=> 0x00005555560f49cd <+1221>:	movb   $0x0,(%rax)

 	    movq  %gs:(0x30), %r10
	    /* restore fiber local storage */
	    movq  0xb0(%rsp), %rax
	    movq  %rax, 0x20(%r10)
	    /* restore current deallocation stack */
	    movq  0xb8(%rsp), %rax
	    movq  %rax, 0x1478(%r10)
	    /* restore current stack limit */
	    movq  0xc0(%rsp), %rax
	    movq  %rax, 0x10(%r10)
	    /* restore current stack base */
	    movq  0xc8(%rsp), %rax
	    movq  %rax, 0x08(%r10)

    void *func2_thread_stack = NULL;
    __sanitizer_start_switch_fiber(&func2_thread_stack,uctx_func1.uc_stack.ss_sp,uctx_func1.uc_stack.ss_size);
    ……… (swap from func2 to func1, and then func1 swap back func2)
    __sanitizer_finish_switch_fiber(func2_thread_stack, &from_stack, &from_stacksize);

context-impl=ucontext -DBOOST_USE_ASAN -DBOOST_USE_UCONTEXT

// Fiber annotation interface.
// Before switching to a different stack, one must call
// __sanitizer_start_switch_fiber with a pointer to the bottom of the
// destination stack and its size. When code starts running on the new stack,
// it must call __sanitizer_finish_switch_fiber to finalize the switch.
// The start_switch function takes a void** to store the current fake stack if
// there is one (it is needed when detect_stack_use_after_return is enabled).
// When restoring a stack, this pointer must be given to the finish_switch
// function. In most cases, this void* can be stored on the stack just before
// switching. When leaving a fiber definitely, null must be passed as first
// argument to the start_switch function so that the fake stack is destroyed.
// If you do not want support for stack use-after-return detection, you can
// always pass null to these two functions.
// Note that the fake stack mechanism is disabled during fiber switch, so if a
// signal callback runs during the switch, it will not benefit from the stack
// use-after-return detection.
void __sanitizer_start_switch_fiber(void **fake_stack_save,
                                    const void *bottom, size_t size);

void __sanitizer_finish_switch_fiber(void *fake_stack_save,
                                     const void **bottom_old,
                                     size_t *size_old);

//vthctx: Context of main fiber/coroutine
//vth:  Context of fiber/coroutine A 

Step1: Try to exchange from main fiber to fiber A =========================================================================:
//On the main fiber.

//Argument0: The container for asan to allocate the fake_stack for current fiber.
//           - If we want the current fiber to stay still(we are going to jump back later),then one valid pointer(&vthctx->fake_stack here) shall be passed to argument 0 to store the fake_stack of current fiber;
//           - If we don't want to keep the current fiber alive(we won't jump back), 'NULL' shall be passed to argument 0 to notify asan to delete the fake_stack of current fiber.
//Argument1: The info of target fiber we are going to jump to.
//Argument2: The info of target fiber we are going to jump to.
__sanitizer_start_switch_fiber(&vthctx->fake_stack, vth->uctx.uc_stack.ss_sp, vth->uctx.uc_stack.ss_size);

//exchange to target fiber A. 
swapcontext(&vthctx->tmp_outer_uctx, &vth->uctx);

Step2: On the trigger function of fiber A =========================================================================:
//On the fiber A
const void *from_stack;
size_t from_stacksize;

//Argument0: We are the first time to jump into this fiber, so NULL shall be set as argument 0;
//           - Set argument 0 to 'NULL' means that we have no historical stack to restore for this fiber;
//           - If we have been to this fiber and have historical stack to restore for this fiber, then set the historical stack to argument 0.  
//Argument1: The container for asan to return the info of old fiber we were in before we jumped over.
//Argument2: The container for asan to return the info of old fiber we were in before we jumped over.
__sanitizer_finish_switch_fiber(NULL, &from_stack, &from_stacksize);

 Step3: jump back from fiber A to main fiber=========================================================================:
//Argument0: To store the fake_stack of old fiber before jumping out.
//           - Pass 'NULL' to argument 0 if we won't jump back to fiber A, then asan will delete the fake_stack of fiber A for us.
//           - Pass '&vth->fake_stack'to argument 0 if we plan to keep fiber A alive and we will jump back in the future，and asan will keep the fake_stack of fiber A for us.
//Argument1: The info of target fiber we are going to jump to.
//Argument2: The info of target fiber we are going to jump to.
__sanitizer_start_switch_fiber(NULL, vthctx->tmp_outer_uctx.uc_stack.ss_sp, vthctx->tmp_outer_uctx.uc_stack.ss_size);
 
//exchange to main fiber.  
swapcontext(&vth->uctx, &vthctx->tmp_outer_uctx);

Step4: Restore the fake_stack on main fiber =========================================================================:
//At the point of the main fiber we're jumping back to

//Argument0: The fake_stack sotred before(see Step1),also the one we try to restore for this fiber.
//Argument1: The container for asan to return the info of old fiber we were in before we jumped over.
//Argument2: The container for asan to return the info of old fiber we were in before we jumped over.
__sanitizer_finish_switch_fiber(vthctx->fake_stack, &from_stack, &from_stacksize);