path: root/kernel
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authorSteven Rostedt <srostedt@redhat.com>2009-06-18 12:53:21 -0400
committerSteven Rostedt <rostedt@goodmis.org>2009-06-18 18:39:30 -0400
commiteb4a03780d4c4464ef2ad86d80cca3f3284fe81d (patch)
tree5bf249073e7c5dec68ced1411b78b4bcf41660b7 /kernel
parent4b221f0313f0f7f1f7aa0a1fd16ad400840def26 (diff)
function-graph: disable when both x86_32 and optimize for size are configured
On x86_32, when optimize for size is set, gcc may align the frame pointer and make a copy of the the return address inside the stack frame. The return address that is located in the stack frame may not be the one used to return to the calling function. This will break the function graph tracer. The function graph tracer replaces the return address with a jump to a hook function that can trace the exit of the function. If it only replaces a copy, then the hook will not be called when the function returns. Worse yet, when the parent function returns, the function graph tracer will return back to the location of the child function which will easily crash the kernel with weird results. To see the problem, when i386 is compiled with -Os we get: c106be03: 57 push %edi c106be04: 8d 7c 24 08 lea 0x8(%esp),%edi c106be08: 83 e4 e0 and $0xffffffe0,%esp c106be0b: ff 77 fc pushl 0xfffffffc(%edi) c106be0e: 55 push %ebp c106be0f: 89 e5 mov %esp,%ebp c106be11: 57 push %edi c106be12: 56 push %esi c106be13: 53 push %ebx c106be14: 81 ec 8c 00 00 00 sub $0x8c,%esp c106be1a: e8 f5 57 fb ff call c1021614 <mcount> When it is compiled with -O2 instead we get: c10896f0: 55 push %ebp c10896f1: 89 e5 mov %esp,%ebp c10896f3: 83 ec 28 sub $0x28,%esp c10896f6: 89 5d f4 mov %ebx,0xfffffff4(%ebp) c10896f9: 89 75 f8 mov %esi,0xfffffff8(%ebp) c10896fc: 89 7d fc mov %edi,0xfffffffc(%ebp) c10896ff: e8 d0 08 fa ff call c1029fd4 <mcount> The compile with -Os will align the stack pointer then set up the frame pointer (%ebp), and it copies the return address back into the stack frame. The change to the return address in mcount is done to the copy and not the real place holder of the return address. Then compile with -O2 sets up the frame pointer first, this makes the change to the return address by mcount affect where the function will jump on exit. Reported-by: Jake Edge <jake@lwn.net> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel')
1 files changed, 1 insertions, 0 deletions
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 4a13e5a01ce..1eac85253ce 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -121,6 +121,7 @@ config FUNCTION_GRAPH_TRACER
bool "Kernel Function Graph Tracer"
+ depends on !X86_32 || !CC_OPTIMIZE_FOR_SIZE
default y
Enable the kernel to trace a function at both its return