Re: [PATCH] i386: Replace internal_function attribute for __mcount_internal

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Mon, Aug 14, 2017 at 11:39 AM, Florian Weimer <fweimer@redhat.com> wrote:
> On 08/14/2017 07:09 PM, H.J. Lu wrote:
>> On Mon, Aug 14, 2017 at 9:34 AM, Florian Weimer <fweimer@redhat.com> wrote:
>>> I compiled glibc on i386 with internal_function restored, with a special
>>> GCC which encodes the regparm attribute value in the symbol name
>>> (similar to what Windows does).  This means that mismatches between
>>> definition and use result in linker errors.
>>>
>>> This rediscovered the NSS mismatch already fixed, and another internal
>>> mismatch related to mcount.  This one is harmless; it's merely an
>>> internal inconsistency introduced by the internal_function removal.
>>>
>>> After adjusting the Versions files to export the mangled names for
>>> GLIBC_PRIVATE functions, all libraries link again and the public ABI
>>> checks out, so I'm reasonably confident that we now have a consistent
>>> build again.
>
>> Is it possible to add a run-time test?
>
> I don't know.  I expect a basic _mcount/profiling/gprof test to catch
> this.  I don't think the calling convention is accidentally compatible.
> Some care is needed to avoid linking with system profiling libraries
> instead of the freshly build glibc.  I don't know how to do that.  I
> doubt that simply building and linking a test with -pg is sufficient.
>
> Thanks,
> Florian

Here is a simple test on Fedora 26.

[hjl@gnu-6 tmp]$ cat foo.c
#include <stdio.h>

void
foo (void)
{
  printf ("hello\n");
}

int
main ()
{
  foo ();
  return 0;
}
[hjl@gnu-6 tmp]$ gcc -c -pg foo.c
[hjl@gnu-6 tmp]$ gcc -v -pg foo.o -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/7/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap
--enable-languages=c,c++,objc,obj-c++,fortran,ada,go,lto --prefix=/usr
--mandir=/usr/share/man --infodir=/usr/share/info
--with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-shared
--enable-threads=posix --enable-checking=release --enable-multilib
--with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-gnu-unique-object
--enable-linker-build-id --with-gcc-major-version-only
--with-linker-hash-style=gnu --enable-plugin --enable-initfini-array
--with-isl --enable-libmpx --enable-offload-targets=nvptx-none
--without-cuda-driver --enable-gnu-indirect-function
--with-tune=generic --with-arch_32=i686
--with-multilib-list=m32,m64,mx32 --build=x86_64-redhat-linux
Thread model: posix
gcc version 7.1.1 20170709 (Red Hat 7.1.1-4) (GCC)
COMPILER_PATH=/usr/libexec/gcc/x86_64-redhat-linux/7/:/usr/libexec/gcc/x86_64-redhat-linux/7/:/usr/libexec/gcc/x86_64-redhat-linux/:/usr/lib/gcc/x86_64-redhat-linux/7/:/usr/lib/gcc/x86_64-redhat-linux/
LIBRARY_PATH=/usr/lib/gcc/x86_64-redhat-linux/7/:/usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64/:/lib/../lib64/:/usr/lib/../lib64/:/usr/lib/gcc/x86_64-redhat-linux/7/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-pg' '-v' '-mtune=generic' '-march=x86-64'
 /usr/libexec/gcc/x86_64-redhat-linux/7/collect2 -plugin
/usr/libexec/gcc/x86_64-redhat-linux/7/liblto_plugin.so
-plugin-opt=/usr/libexec/gcc/x86_64-redhat-linux/7/lto-wrapper
-plugin-opt=-fresolution=/tmp/cc4bjCNr.res
-plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lgcc_s
-plugin-opt=-pass-through=-lc -plugin-opt=-pass-through=-lgcc
-plugin-opt=-pass-through=-lgcc_s --build-id --no-add-needed
--eh-frame-hdr --hash-style=gnu -m elf_x86_64 -dynamic-linker
/lib64/ld-linux-x86-64.so.2
/usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64/gcrt1.o
/usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64/crti.o
/usr/lib/gcc/x86_64-redhat-linux/7/crtbegin.o
-L/usr/lib/gcc/x86_64-redhat-linux/7
-L/usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64 -L/lib/../lib64
-L/usr/lib/../lib64 -L/usr/lib/gcc/x86_64-redhat-linux/7/../../..
foo.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed
-lgcc_s --no-as-needed /usr/lib/gcc/x86_64-redhat-linux/7/crtend.o
/usr/lib/gcc/x86_64-redhat-linux/7/../../../../lib64/crtn.o
COLLECT_GCC_OPTIONS='-v' '-pg' '-v' '-mtune=generic' '-march=x86-64'
[hjl@gnu-6 tmp]$ ./a.out
hello
[hjl@gnu-6 tmp]$ gprof a.out
Flat profile:

Each sample counts as 0.01 seconds.
 no time accumulated

  %   cumulative   self              self     total
 time   seconds   seconds    calls  Ts/call  Ts/call  name
  0.00      0.00     0.00        1     0.00     0.00  foo

 %         the percentage of the total running time of the
time       program used by this function.

cumulative a running sum of the number of seconds accounted
 seconds   for by this function and those listed above it.

 self      the number of seconds accounted for by this
seconds    function alone.  This is the major sort for this
           listing.

calls      the number of times this function was invoked, if
           this function is profiled, else blank.

 self      the average number of milliseconds spent in this
ms/call    function per call, if this function is profiled,
  else blank.

 total     the average number of milliseconds spent in this
ms/call    function and its descendents per call, if this
  function is profiled, else blank.

name       the name of the function.  This is the minor sort
           for this listing. The index shows the location of
  the function in the gprof listing. If the index is
  in parenthesis it shows where it would appear in
  the gprof listing if it were to be printed.


Copyright (C) 2012-2017 Free Software Foundation, Inc.

Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved.


    Call graph (explanation follows)


granularity: each sample hit covers 2 byte(s) no time propagated

index % time    self  children    called     name
                0.00    0.00       1/1           main [7]
[1]      0.0    0.00    0.00       1         foo [1]
-----------------------------------------------

 This table describes the call tree of the program, and was sorted by
 the total amount of time spent in each function and its children.

 Each entry in this table consists of several lines.  The line with the
 index number at the left hand margin lists the current function.
 The lines above it list the functions that called this function,
 and the lines below it list the functions this one called.
 This line lists:
     index A unique number given to each element of the table.
Index numbers are sorted numerically.
The index number is printed next to every function name so
it is easier to look up where the function is in the table.

     % time This is the percentage of the `total' time that was spent
in this function and its children.  Note that due to
different viewpoints, functions excluded by options, etc,
these numbers will NOT add up to 100%.

     self This is the total amount of time spent in this function.

     children This is the total amount of time propagated into this
function by its children.

     called This is the number of times the function was called.
If the function called itself recursively, the number
only includes non-recursive calls, and is followed by
a `+' and the number of recursive calls.

     name The name of the current function.  The index number is
printed after it.  If the function is a member of a
cycle, the cycle number is printed between the
function's name and the index number.


 For the function's parents, the fields have the following meanings:

     self This is the amount of time that was propagated directly
from the function into this parent.

     children This is the amount of time that was propagated from
the function's children into this parent.

     called This is the number of times this parent called the
function `/' the total number of times the function
was called.  Recursive calls to the function are not
included in the number after the `/'.

     name This is the name of the parent.  The parent's index
number is printed after it.  If the parent is a
member of a cycle, the cycle number is printed between
the name and the index number.

 If the parents of the function cannot be determined, the word
 `<spontaneous>' is printed in the `name' field, and all the other
 fields are blank.

 For the function's children, the fields have the following meanings:

     self This is the amount of time that was propagated directly
from the child into the function.

     children This is the amount of time that was propagated from the
child's children to the function.

     called This is the number of times the function called
this child `/' the total number of times the child
was called.  Recursive calls by the child are not
listed in the number after the `/'.

     name This is the name of the child.  The child's index
number is printed after it.  If the child is a
member of a cycle, the cycle number is printed
between the name and the index number.

 If there are any cycles (circles) in the call graph, there is an
 entry for the cycle-as-a-whole.  This entry shows who called the
 cycle (as parents) and the members of the cycle (as children.)
 The `+' recursive calls entry shows the number of function calls that
 were internal to the cycle, and the calls entry for each member shows,
 for that member, how many times it was called from other members of
 the cycle.


Copyright (C) 2012-2017 Free Software Foundation, Inc.

Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved.


Index by function name

   [1] foo
[hjl@gnu-6 tmp]$

We don't profile gliibc.


-- 
H.J.