[uml-devel] [PATCH] um: support kcov

[Vegard N. <veg...@or...>]

This adds support for kcov to UML.

There is a small problem where UML will randomly segfault during boot;
this is because current_thread_info() occasionally returns an invalid
(non-NULL) pointer and we try to dereference it in
__sanitizer_cov_trace_pc(). I consider this a bug in UML itself and this
patch merely exposes it.

Cc: Quentin Casasnovas <que...@or...>
Cc: Richard Weinberger <ri...@no...>
Cc: Thomas Meyer <th...@m3...>
Cc: user-mode-linux-devel <use...@li...>
Cc: Dmitry Vyukov <dv...@go...>
Signed-off-by: Vegard Nossum <veg...@or...>
---
 arch/um/Kconfig.common    | 1 +
 arch/x86/um/vdso/Makefile | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/arch/um/Kconfig.common b/arch/um/Kconfig.common
index cc00134..64c1d46 100644
--- a/arch/um/Kconfig.common
+++ b/arch/um/Kconfig.common
@@ -1,6 +1,7 @@
 config UML
 	bool
 	default y
+	select ARCH_HAS_KCOV
 	select HAVE_ARCH_AUDITSYSCALL
 	select HAVE_ARCH_SECCOMP_FILTER
 	select HAVE_UID16
diff --git a/arch/x86/um/vdso/Makefile b/arch/x86/um/vdso/Makefile
index 6c803ca..d72dec4 100644
--- a/arch/x86/um/vdso/Makefile
+++ b/arch/x86/um/vdso/Makefile
@@ -2,6 +2,9 @@
 # Building vDSO images for x86.
 #
 
+# Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
+KCOV_INSTRUMENT                := n
+
 VDSO64-y		:= y
 
 vdso-install-$(VDSO64-y)	+= vdso.so
-- 
1.9.1