[asan][test] Several Posix/unpoison-alternate-stack.cpp fixes

[ro]

Summary

Posix/unpoison-alternate-stack.cpp currently FAILs on Solaris/i386 and the investigation revealed several generic problems:

• clang warns compiling the testcase:

/vol/llvm/src/llvm-project/local/compiler-rt/test/asan/TestCases/Posix/unpoison-alternate-stack.cpp:83:7: warning: nested designators are a C99 extension [-Wc99-designator]
      .sa_sigaction = signalHandler,
      ^~~~~~~~~~~~~
/vol/llvm/src/llvm-project/local/compiler-rt/test/asan/TestCases/Posix/unpoison-alternate-stack.cpp:84:7: warning: ISO C++ requires field designators to be specified in declaration order; field '_funcptr' will be initialized after field 'sa_flags' [-Wreorder-init-list]
      .sa_flags = SA_SIGINFO | SA_NODEFER | SA_ONSTACK,
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/vol/llvm/src/llvm-project/local/compiler-rt/test/asan/TestCases/Posix/unpoison-alternate-stack.cpp:83:8: note: previous initialization for field '_funcptr' is here
      .sa_sigaction = signalHandler,
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/sys/signal.h:71:30: note: expanded from macro 'sa_sigaction'
#define sa_sigaction    _funcptr._sigaction
                                ^
/vol/llvm/src/llvm-project/local/compiler-rt/test/asan/TestCases/Posix/unpoison-alternate-stack.cpp:149:7: warning: ISO C++ requires field designators to be specified in declaration order; field 'ss_flags' will be initialized after field 'ss_size' [-Wreorder-init-list]
      .ss_size = AltStackSize,
      ^~~~~~~~~~~~~~~~~~~~~~~
/vol/llvm/src/llvm-project/local/compiler-rt/test/asan/TestCases/Posix/unpoison-alternate-stack.cpp:148:19: note: previous initialization for field 'ss_flags' is here
      .ss_flags = 0,
                  ^

This can all easily be avoided by initializing each field separately.

• The test SEGVs:

Thread 4 received signal SIGSEGV, Segmentation fault.
[Switching to Thread 2 (LWP 2)]
0x08157f0f in __asan_memcpy (to=0xfe5d2e30, from=0x808cda0 <__const._ZN12_GLOBAL__N_123setSignalAlternateStackEPv.Action>, size=32) at /vol/llvm/src/llvm-project/dist/compiler-rt/lib/asan/asan_interceptors_memintrinsics.cpp:21
21	void *__asan_memcpy(void *to, const void *from, uptr size) {
(gdb) where
#0  0x08157f0f in __asan_memcpy (to=0xfe5d2e30, from=0x808cda0 <__const._ZN12_GLOBAL__N_123setSignalAlternateStackEPv.Action>, size=32) at /vol/llvm/src/llvm-project/dist/compiler-rt/lib/asan/asan_interceptors_memintrinsics.cpp:21
#1  0x081b080e in (anonymous namespace)::setSignalAlternateStack(void*) () at /vol/llvm/src/llvm-project/dist/compiler-rt/test/asan/TestCases/Posix/unpoison-alternate-stack.cpp:86
#2  0x081b02bc in (anonymous namespace)::threadFun(void*) () at /vol/llvm/src/llvm-project/dist/compiler-rt/test/asan/TestCases/Posix/unpoison-alternate-stack.cpp:107
#3  0x0816dd2a in __asan::AsanThread::ThreadStart (this=0xfe3f3000, os_id=2, signal_thread_is_registered=0xfeffd724) at /vol/llvm/src/llvm-project/dist/compiler-rt/lib/asan/asan_thread.cpp:262
#4  0x081400d0 in asan_thread_start (arg=0xfeffd720) at /vol/llvm/src/llvm-project/dist/compiler-rt/lib/asan/asan_interceptors.cpp:205
#5  0xfe281d3b in _thrp_setup () from /lib/libc.so.1
#6  0xfe282090 in ?? () from /lib/libc.so.1

in the sequence determing the GOT address at the `calll` insn:

	subl	$5424, %esp                     # imm = 0x1530
	calll	.L1$pb
.L1$pb:

The problem is that the default Solaris/i386 stack size is only 4 kB, while `__asan_memcpy` tries to allocate either 5436 (32-bit) or 10688 bytes (64-bit) on the stack.  This patch avoids this by requiring at least 16 kB stack size.

• When I later investigated PlatformUnpoisonStacks calling GetThreadStackAndTls, I was reminded that GetTls is a dummy on Solaris. I do have a (not yet fully portable) implemtation, however that's moot for this testcase.
• Even without -fsanitize=address or in a minimal testcase derived from this one, I get an assertion failure:

Assertion failed: !isOnSignalStack(), file /vol/llvm/src/llvm-project/dist/compiler-rt/test/asan/TestCases/Posix/unpoison-alternate-stack.cpp, line 117

The fundamental problem with this testcase is that `longjmp` from a signal handler is highly unportable; XPG7 strongly warns against it and it is thus unspecified which stack is used when `longjmp`ing from a signal handler running on an alternative stack.

So I'm XFAILing this testcases on Solaris.

Tested on amd64-pc-solaris2.11 and x86_64-pc-linux-gnu.

[vitalybuka]

Please do not include entire description into git commit.
A couple of sentences should be enough.

compiler-rt/test/asan/TestCases/Posix/unpoison-alternate-stack.cpp

89–91

156–159

same

[ro]

compiler-rt/test/asan/TestCases/Posix/unpoison-alternate-stack.cpp

89–91

This doesn't compile on Linux/x86_64:

/vol/llvm/src/llvm-project/local/compiler-rt/test/asan/TestCases/Posix/unpoison-alternate-stack.cpp:89:3: error: must use 'struct' tag to refer to type 'sigaction' in this scope
  sigaction Action = {};
  ^
  struct

Will go for

struct sigaction Action = {};

instead.

compiler-rt/test/asan/TestCases/Posix/unpoison-alternate-stack.cpp

 // Tests that __asan_handle_no_return properly unpoisons the signal alternate
 // stack.
 
 // Don't optimize, otherwise the variables which create redzones might be
 // dropped.
 // RUN: %clangxx_asan -std=c++20 -fexceptions -O0 %s -o %t -pthread
 // RUN: %run %t
 
 // XFAIL: ios && !iossim
+// longjmp from signal handler is unportable.
+// XFAIL: solaris
 
+#include <algorithm>
 #include <cassert>
 #include <cerrno>
 #include <csetjmp>
 #include <cstdint>
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
 
void signalHandler(int, siginfo_t *, void *) {
 
   // test unpoisoning when jumping between stacks
   poisonStackAndJump(signalStack, [] { longjmp(defaultStack.JmpBuf, 1); });
 }
 
 void setSignalAlternateStack(void *AltStack) {
   sigaltstack((stack_t const *)AltStack, nullptr);
 
-  struct sigaction Action = {
-      .sa_sigaction = signalHandler,
-      .sa_flags = SA_SIGINFO | SA_NODEFER | SA_ONSTACK,
-  };
+  struct sigaction Action = {};
+  Action.sa_sigaction = signalHandler;
+  Action.sa_flags = SA_SIGINFO | SA_NODEFER | SA_ONSTACK;
   sigemptyset(&Action.sa_mask);
 
   sigaction(SIGUSR1, &Action, nullptr);
 }
 
 // Main test function.
 // Must be run on another thread to be able to control memory placement between
 // default stack and alternate signal stack.

 // Check that __asan_handle_no_return properly unpoisons a signal alternate
 // stack.
 // __asan_handle_no_return tries to determine the stack boundaries and
 // unpoisons all memory inside those. If this is not done properly, redzones for
 // variables on can remain in shadow memory which might lead to false positive
 // reports when the stack is reused.
 int main() {
   size_t const PageSize = sysconf(_SC_PAGESIZE);
+  // The Solaris defaults of 4k (32-bit) and 8k (64-bit) are too small.
+  size_t const MinStackSize = std::max(PTHREAD_STACK_MIN, 16 * 1024);
   // To align the alternate stack, we round this up to page_size.
   size_t const DefaultStackSize =
-      (PTHREAD_STACK_MIN - 1 + PageSize) & ~(PageSize - 1);
+      (MinStackSize - 1 + PageSize) & ~(PageSize - 1);
   // The alternate stack needs a certain size, or the signal handler segfaults.
   size_t const AltStackSize = 10 * PageSize;
   size_t const MappingSize = DefaultStackSize + AltStackSize;
   // Using mmap guarantees proper alignment.
   void *const Mapping = mmap(nullptr, MappingSize,
                              PROT_READ | PROT_WRITE,
                              MAP_PRIVATE | MAP_ANONYMOUS,
                              -1, 0);
 
-  stack_t const AltStack = {
-      .ss_sp = (char *)Mapping + DefaultStackSize,
-      .ss_flags = 0,
-      .ss_size = AltStackSize,
-  };
+  stack_t AltStack = {};
+  AltStack.ss_sp = (char *)Mapping + DefaultStackSize;
+  AltStack.ss_flags = 0;
+  AltStack.ss_size = AltStackSize;
 
   pthread_t Thread;
   pthread_attr_t ThreadAttr;
   pthread_attr_init(&ThreadAttr);
   pthread_attr_setstack(&ThreadAttr, Mapping, DefaultStackSize);
   pthread_create(&Thread, &ThreadAttr, &threadFun, (void *)&AltStack);
 
   pthread_join(Thread, nullptr);
 
   munmap(Mapping, MappingSize);
 }