From 444758636439810f110f86a3042c2dfd3626a9e2 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Fri, 15 Oct 2010 11:49:47 -0400 Subject: [PATCH 1/2] ftrace: Do not process kernel/trace/ftrace.o with C recordmcount program The file kernel/trace/ftrace.c references the mcount() call to convert the mcount() callers to nops. But because it references mcount(), the mcount() address is placed in the relocation table. The C version of recordmcount reads the relocation table of all object files, and it will add all references to mcount to the __mcount_loc table that is used to find the places that call mcount() and change the call to a nop. When recordmcount finds the mcount reference in kernel/trace/ftrace.o, it saves that location even though the code is not a call, but references mcount as data. On boot up, when all calls are converted to nops, the code has a safety check to determine what op code it is actually replacing before it replaces it. If that op code at the address does not match, then a warning is printed and the function tracer is disabled. The reference to mcount in ftrace.c, causes this warning to trigger, since the reference is not a call to mcount(). The ftrace.c file is not compiled with the -pg flag, so no calls to mcount() should be expected. This patch simply makes recordmcount.c skip the kernel/trace/ftrace.c file. This was the same solution used by the perl version of recordmcount. Reported-by: Ingo Molnar Cc: John Reiser Signed-off-by: Steven Rostedt --- scripts/recordmcount.c | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-) diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c index 7f7f7180fe24..26e1271259ba 100644 --- a/scripts/recordmcount.c +++ b/scripts/recordmcount.c @@ -313,12 +313,30 @@ do_file(char const *const fname) int main(int argc, char const *argv[]) { + const char ftrace[] = "kernel/trace/ftrace.o"; + int ftrace_size = sizeof(ftrace) - 1; int n_error = 0; /* gcc-4.3.0 false positive complaint */ - if (argc <= 1) + + if (argc <= 1) { fprintf(stderr, "usage: recordmcount file.o...\n"); - else /* Process each file in turn, allowing deep failure. */ + return 0; + } + + /* Process each file in turn, allowing deep failure. */ for (--argc, ++argv; 0 < argc; --argc, ++argv) { int const sjval = setjmp(jmpenv); + int len; + + /* + * The file kernel/trace/ftrace.o references the mcount + * function but does not call it. Since ftrace.o should + * not be traced anyway, we just skip it. + */ + len = strlen(argv[0]); + if (len >= ftrace_size && + strcmp(argv[0] + (len - ftrace_size), ftrace) == 0) + continue; + switch (sjval) { default: { fprintf(stderr, "internal error: %s\n", argv[0]); From 85caa993d7f218b7c2abcfcb28e212396b6a3313 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Fri, 15 Oct 2010 12:09:25 -0400 Subject: [PATCH 2/2] ftrace: Use objtree for C version of recordmcount The C version of recordmcount is compiled to a binary, which will end up located in the objtree. If the kernel is built with O=path, the srctree will not include the binary recordmcount caller. Cc: Michal Marek Cc: linux-kbuild@vger.kernel.org Signed-off-by: Steven Rostedt --- scripts/Makefile.build | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/scripts/Makefile.build b/scripts/Makefile.build index 4d03a7efc689..4db60b2e2a76 100644 --- a/scripts/Makefile.build +++ b/scripts/Makefile.build @@ -210,7 +210,7 @@ endif ifdef CONFIG_FTRACE_MCOUNT_RECORD ifdef BUILD_C_RECORDMCOUNT -cmd_record_mcount = $(srctree)/scripts/recordmcount "$(@)"; +cmd_record_mcount = $(objtree)/scripts/recordmcount "$(@)"; else cmd_record_mcount = set -e ; perl $(srctree)/scripts/recordmcount.pl "$(ARCH)" \ "$(if $(CONFIG_CPU_BIG_ENDIAN),big,little)" \