Re: [PATCH] Add -fno-instrument-function

[Richard Biener <richard dot guenther at gmail dot com>]

On Mon, Sep 1, 2014 at 10:25 PM, Andi Kleen <andi@firstfloor.org> wrote:
> From: Andi Kleen <ak@linux.intel.com>
>
> [This was an old patch of mine that has been posted before,
> but never made it in]
>
> This adds a new C/C++ option to force
> __attribute__((no_instrument_function)) on every function compiled.
>
> This is useful together with LTO. You may want to have the whole
> program compiled with -pg and have to specify that in the LTO
> link, but want to disable it for some specific files. As the
> option works on the frontend level it is already passed through
> properly by LTO.
>
> Without LTO it is equivalent to not specifing -pg or -mfentry.
>
> This fixes some missing functionality in the Linux kernel LTO port,
> in particular it allows using the function tracer with LTO kernels.
>
> Longer term it would be nicer if all suitable options were handled
> like this for LTO by turning them into attributes, but that would
> be a much larger project.
>
> Passed bootstrap and test suite on x86_64-linux. Ok?

Hmm, why not make -no-pg (does that exist?) and/or -mno-fentry
do this?  That is, I don't see the need for a new option.

Or do it the other way around - change the default to
DECL_NO_INSTRUMENT_FUNCTION_ENTRY_EXIT and make
-pg/-mfentry unset that (or have DECL_INSTRUMENT_FUNCTION_ENTRY_EXIT).

Richard.

> gcc/:
>
> 2014-09-01  Andi Kleen <ak@linux.intel.com>
>
>         * c.opt (fno-instrument-function): Document.
>
> gcc/c:
>
> 2014-09-01  Andi Kleen <ak@linux.intel.com>
>
>         * c-decl.c (start_function): Handle force_no_instrument_function
>
> gcc/cp:
>
> 2014-09-01  Andi Kleen <ak@linux.intel.com>
>
>         * decl.c (start_preparsed_function): Handle
>         force_no_instrument_function
>
> gcc/testsuite:
>
> 2014-09-01  Andi Kleen <ak@linux.intel.com>
>
>         * g++.dg/fno-instrument-function.C: Add.
>         * gcc.dg/fno-instrument-function.c: Add.
> ---
>  gcc/c-family/c.opt                             |  4 ++++
>  gcc/c/c-decl.c                                 |  3 +++
>  gcc/cp/decl.c                                  |  3 +++
>  gcc/doc/invoke.texi                            |  8 +++++++-
>  gcc/testsuite/g++.dg/fno-instrument-function.C | 18 ++++++++++++++++++
>  gcc/testsuite/gcc.dg/fno-instrument-function.c | 24 ++++++++++++++++++++++++
>  6 files changed, 59 insertions(+), 1 deletion(-)
>  create mode 100644 gcc/testsuite/g++.dg/fno-instrument-function.C
>  create mode 100644 gcc/testsuite/gcc.dg/fno-instrument-function.c
>
> diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
> index 210a099..2aabd23 100644
> --- a/gcc/c-family/c.opt
> +++ b/gcc/c-family/c.opt
> @@ -1118,6 +1118,10 @@ Enum(ivar_visibility) String(public) Value(IVAR_VISIBILITY_PUBLIC)
>  EnumValue
>  Enum(ivar_visibility) String(package) Value(IVAR_VISIBILITY_PACKAGE)
>
> +fno-instrument-function
> +C C++ ObjC ObjC++ RejectNegative Report Var(force_no_instrument_function)
> +Force __attribute__((no_instrument_function)) for all functions in translation unit.
> +
>  fnonansi-builtins
>  C++ ObjC++ Var(flag_no_nonansi_builtin, 0)
>
> diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
> index b4995a6..493240f 100644
> --- a/gcc/c/c-decl.c
> +++ b/gcc/c/c-decl.c
> @@ -8044,6 +8044,9 @@ start_function (struct c_declspecs *declspecs, struct c_declarator *declarator,
>    if (current_scope == file_scope)
>      maybe_apply_pragma_weak (decl1);
>
> +  if (force_no_instrument_function)
> +    DECL_NO_INSTRUMENT_FUNCTION_ENTRY_EXIT (decl1) = 1;
> +
>    /* Warn for unlikely, improbable, or stupid declarations of `main'.  */
>    if (warn_main && MAIN_NAME_P (DECL_NAME (decl1)))
>      {
> diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
> index d03f8a4..505ad50 100644
> --- a/gcc/cp/decl.c
> +++ b/gcc/cp/decl.c
> @@ -13251,6 +13251,9 @@ start_preparsed_function (tree decl1, tree attrs, int flags)
>        && lookup_attribute ("noinline", attrs))
>      warning (0, "inline function %q+D given attribute noinline", decl1);
>
> +  if (force_no_instrument_function)
> +    DECL_NO_INSTRUMENT_FUNCTION_ENTRY_EXIT (decl1) = 1;
> +
>    /* Handle gnu_inline attribute.  */
>    if (GNU_INLINE_P (decl1))
>      {
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index d15d4a9..51b8d20 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -169,7 +169,7 @@ in the following sections.
>  -aux-info @var{filename} -fallow-parameterless-variadic-functions @gol
>  -fno-asm  -fno-builtin  -fno-builtin-@var{function} @gol
>  -fhosted  -ffreestanding -fopenmp -fopenmp-simd -fms-extensions @gol
> --fplan9-extensions -trigraphs  -traditional  -traditional-cpp @gol
> +-fplan9-extensions -trigraphs  -traditional  -traditional-cpp -fno-instrument-function @gol
>  -fallow-single-precision  -fcond-mismatch -flax-vector-conversions @gol
>  -fsigned-bitfields  -fsigned-char @gol
>  -funsigned-bitfields  -funsigned-char}
> @@ -1971,6 +1971,12 @@ Allow implicit conversions between vectors with differing numbers of
>  elements and/or incompatible element types.  This option should not be
>  used for new code.
>
> +@item -fno-instrument-function
> +@opindex fno-instrument-function
> +Override @option{-pg} for this translation unit. This is useful with
> +Link Time Optimization (LTO) to override the effects of -pg for a
> +specific source file.
> +
>  @item -funsigned-char
>  @opindex funsigned-char
>  Let the type @code{char} be unsigned, like @code{unsigned char}.
> diff --git a/gcc/testsuite/g++.dg/fno-instrument-function.C b/gcc/testsuite/g++.dg/fno-instrument-function.C
> new file mode 100644
> index 0000000..e2f6518
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/fno-instrument-function.C
> @@ -0,0 +1,18 @@
> +/* Test -fno-instrument-function */
> +/* { dg-do compile } */
> +/* { dg-options "-pg -fno-instrument-function" } */
> +/* { dg-final { scan-assembler-not "mcount" } } */
> +/* Origin: Andi Kleen */
> +extern void foobar(const char *);
> +
> +void func(void)
> +{
> +  foobar ("Hello world\n");
> +}
> +
> +void func2(void)
> +{
> +  int i;
> +  for (i = 0; i < 10; i++)
> +    foobar ("Hello world");
> +}
> diff --git a/gcc/testsuite/gcc.dg/fno-instrument-function.c b/gcc/testsuite/gcc.dg/fno-instrument-function.c
> new file mode 100644
> index 0000000..9c68fa8
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/fno-instrument-function.c
> @@ -0,0 +1,24 @@
> +/* Test -fno-instrument-function */
> +/* { dg-do compile } */
> +/* { dg-options "-pg -fno-instrument-function" } */
> +/* { dg-final { scan-assembler-not "mcount" } } */
> +/* Origin: Andi Kleen */
> +extern void foobar(char *);
> +
> +void func(void)
> +{
> +  foobar ("Hello world\n");
> +}
> +
> +void func2(void)
> +{
> +  int i;
> +  for (i = 0; i < 10; i++)
> +    foobar ("Hello world");
> +}
> +
> +void func3(a)
> +char *a;
> +{
> +  foobar("Hello world");
> +}
> --
> 2.1.0
>