sigframe construction for x86-linux: ensure that ESP is correctly aligned before...

Without this, a signal handler compiled by Clang 6, which uses movdqa to load/store
relative to ESP, segfaults because the resulting address isn't 16-aligned.

diff --git a/coregrind/m_sigframe/sigframe-x86-linux.c b/coregrind/m_sigframe/sigframe-x86-linux.c
index 27ca4c2aa00cc6c4d4cc204aad63ad0fa4df2f48..63bcf196e03af36704ca923c2bbb5ce9ffd0b229 100644 (file)
--- a/coregrind/m_sigframe/sigframe-x86-linux.c
+++ b/coregrind/m_sigframe/sigframe-x86-linux.c
@@ -430,7 +430,7 @@ static Addr build_sigframe(ThreadState *tst,
    vg_assert((flags & VKI_SA_SIGINFO) == 0);
 
    esp -= sizeof(*frame);
-   esp = VG_ROUNDDN(esp, 16);
+   esp = VG_ROUNDDN(esp, 16) - 4;
    frame = (struct sigframe *)esp;
 
    if (! ML_(sf_maybe_extend_stack)(tst, esp, sizeof(*frame), flags))
@@ -487,7 +487,7 @@ static Addr build_rt_sigframe(ThreadState *tst,
    vg_assert((flags & VKI_SA_SIGINFO) != 0);
 
    esp -= sizeof(*frame);
-   esp = VG_ROUNDDN(esp, 16);
+   esp = VG_ROUNDDN(esp, 16) - 4;
    frame = (struct rt_sigframe *)esp;
 
    if (! ML_(sf_maybe_extend_stack)(tst, esp, sizeof(*frame), flags))