path: root/arch/x86/Makefile_32.cpu
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authorThomas Gleixner <tglx@linutronix.de>2009-11-20 11:01:43 (GMT)
committerThomas Gleixner <tglx@linutronix.de>2009-11-20 13:06:46 (GMT)
commit746357d6a526d6da9d89a2ec645b28406e959c2e (patch)
tree1ba639c8cd15f94f09cb6c0830a17773f8cc7080 /arch/x86/Makefile_32.cpu
parent303fc0870f8fbfabe260c5c32b18e53458d597ea (diff)
x86: Prevent GCC 4.4.x (pentium-mmx et al) function prologue wreckage
When the kernel is compiled with -pg for tracing GCC 4.4.x inserts stack alignment of a function _before_ the mcount prologue if the -march=pentium-mmx is set and -mtune=generic is not set. This breaks the assumption of the function graph tracer which expects that the mcount prologue push %ebp mov %esp, %ebp is the first stack operation in a function because it needs to modify the function return address on the stack to trap into the tracer before returning to the real caller. The generated code is: push %edi lea 0x8(%esp),%edi and $0xfffffff0,%esp pushl -0x4(%edi) push %ebp mov %esp,%ebp so the tracer modifies the copy of the return address which is stored after the stack alignment and therefor does not trap the return which in turn breaks the call chain logic of the tracer and leads to a kernel panic. Aside of the fact that the generated code is horrible for no good reason other -march -mtune options generate the expected: push %ebp mov %esp,%ebp and $0xfffffff0,%esp which does the same and keeps everything intact. After some experimenting we found out that this problem is restricted to gcc4.4.x and to the following -march settings: i586, pentium, pentium-mmx, k6, k6-2, k6-3, winchip-c6, winchip2, c3, geode By adding -mtune=generic the code generator produces always the expected code. So forcing -mtune=generic when CONFIG_FUNCTION_GRAPH_TRACER=y is not pretty, but at the moment the only way to prevent that the kernel trips over gcc-shrooms induced code madness. Most distro kernels have CONFIG_X86_GENERIC=y anyway which forces -mtune=generic as well so it will not impact those. References: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42109 http://lkml.org/lkml/2009/11/19/17 Signed-off-by: Thomas Gleixner <tglx@linutronix.de> LKML-Reference: <alpine.LFD.2.00.0911200206570.24119@localhost.localdomain> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Ingo Molnar <mingo@elte.hu> Cc: Peter Zijlstra <peterz@infradead.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Frederic Weisbecker <fweisbec@gmail.com>, Cc: Jeff Law <law@redhat.com> Cc: gcc@gcc.gnu.org Cc: David Daney <ddaney@caviumnetworks.com> Cc: Andrew Haley <aph@redhat.com> Cc: Richard Guenther <richard.guenther@gmail.com> Cc: stable@kernel.org
Diffstat (limited to 'arch/x86/Makefile_32.cpu')
1 files changed, 6 insertions, 0 deletions
diff --git a/arch/x86/Makefile_32.cpu b/arch/x86/Makefile_32.cpu
index 30e9a26..df7fdf8 100644
--- a/arch/x86/Makefile_32.cpu
+++ b/arch/x86/Makefile_32.cpu
@@ -46,6 +46,12 @@ cflags-$(CONFIG_MGEODEGX1) += -march=pentium-mmx
# cpu entries
cflags-$(CONFIG_X86_GENERIC) += $(call tune,generic,$(call tune,i686))
+# Work around the pentium-mmx code generator madness of gcc4.4.x which
+# does stack alignment by generating horrible code _before_ the mcount
+# prologue (push %ebp, mov %esp, %ebp) which breaks the function graph
+# tracer assumptions
+cflags-$(CONFIG_FUNCTION_GRAPH_TRACER) += $(call cc-option,-mtune=generic)
# Bug fix for binutils: this option is required in order to keep
# binutils from generating NOPL instructions against our will.
ifneq ($(CONFIG_X86_P6_NOP),y)

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