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fgraph: Fix function type mismatches of ftrace_graph_return using ftrace_stub

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The C compiler is allowing more checks to make sure that function pointers
are assigned to the correct prototype function. Unfortunately, the function
graph tracer uses a special name with its assigned ftrace_graph_return
function pointer that maps to a stub function used by the function tracer
(ftrace_stub). The ftrace_graph_return variable is compared to the
ftrace_stub in some archs to know if the function graph tracer is enabled or
not. This means we can not just simply create a new function stub that
compares it without modifying all the archs.

Instead, have the linker script create a function_graph_stub that maps to
ftrace_stub, and this way we can define the prototype for it to match the
prototype of ftrace_graph_return, and make the compiler checks all happy!

Link: http://lkml.kernel.org/r/20191015090055.789a0aed@gandalf.local.home

Cc: linux-sh@vger.kernel.org
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc:  Rich Felker <dalias@libc.org>
Reported-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (VMware)
2019-10-15 09:00:55 -04:00
parent 953ae45a0c
commit b83b43ffc6
3 changed files with 27 additions and 6 deletions
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17
include/asm-generic/vmlinux.lds.h
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@@ -111,18 +111,29 @@
#ifdef CONFIG_FTRACE_MCOUNT_RECORD
#ifdef CC_USING_PATCHABLE_FUNCTION_ENTRY
/*
* Need to also make ftrace_graph_stub point to ftrace_stub
* so that the same stub location may have different protocols
* and not mess up with C verifiers.
*/
#define MCOUNT_REC() . = ALIGN(8); \
__start_mcount_loc = .; \
KEEP(*(__patchable_function_entries)) \
__stop_mcount_loc = .;
__stop_mcount_loc = .; \
ftrace_graph_stub = ftrace_stub;
#else
#define MCOUNT_REC() . = ALIGN(8); \
__start_mcount_loc = .; \
KEEP(*(__mcount_loc)) \
__stop_mcount_loc = .;
__stop_mcount_loc = .; \
ftrace_graph_stub = ftrace_stub;
#endif
#else
#define MCOUNT_REC()
# ifdef CONFIG_FUNCTION_TRACER
# define MCOUNT_REC() ftrace_graph_stub = ftrace_stub;
# else
# define MCOUNT_REC()
# endif
#endif
#ifdef CONFIG_TRACE_BRANCH_PROFILING