QtTest: Increase the size of the alternate stack

The default (8kB) isn't enough for modern Linux on x86-64. I can't
exactly account for it, as the size of the xsave area is 0x340 bytes,
plus the regular area it's still less than ~1.5 kB. But empirically we
can see that 8kB causes a SIGSEGV when a signal is delivered, while 16
kB works.

Since we're increasing the size, let's make sure it ends up in a
separate page from the rest of the .bss data.

Change-Id: I5d1e6f7607404caa96e4ffff13e84c87c33723c7
Reviewed-by: Jason McDonald <macadder1@gmail.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/src/testlib/qtestcase.cpp b/src/testlib/qtestcase.cpp
index 453288ee82..c96b72bef7 100644
--- a/src/testlib/qtestcase.cpp
+++ b/src/testlib/qtestcase.cpp
@@ -2453,7 +2453,12 @@ FatalSignalHandler::FatalSignalHandler()
 #ifdef SA_ONSTACK
     // Let the signal handlers use an alternate stack
     // This is necessary if SIGSEGV is to catch a stack overflow
-    static char alternate_stack[SIGSTKSZ];
+#  if defined(Q_CC_GNU) && defined(Q_OF_ELF)
+    // Put the alternate stack in the .lbss (large BSS) section so that it doesn't
+    // interfere with normal .bss symbols
+    __attribute__((section(".lbss.altstack"), aligned(4096)))
+#  endif
+    static char alternate_stack[16 * 1024];
     stack_t stack;
     stack.ss_flags = 0;
     stack.ss_size = sizeof alternate_stack;