[PATCH v3] Use __executable_start as the lowest address for profiling [BZ #28153]

["H.J. Lu via Libc-alpha" <libc-alpha@sourceware.org>]

Glibc assumes that ENTRY_POINT is the lowest address for which we need
to keep profiling records and BFD linker uses a linker script to place
the input sections.

Starting from GCC 4.6, the main function is placed in .text.startup
section and starting from binutils 2.22, BFD linker with

commit add44f8d5c5c05e08b11e033127a744d61c26aee
Author: Alan Modra <amodra@gmail.com>
Date:   Thu Nov 25 03:03:02 2010 +0000

            * scripttempl/elf.sc: Group .text.exit, text.startup and .text.hot
            sections.

places .text.startup section before .text section, which leave the main
function out of profiling records.

Starting from binutils 2.15, linker provides __executable_start to mark
the lowest address of the executable.  Use __executable_start as the
lowest address to keep the main function in profiling records. This fixes
[BZ #28153].

Tested on Linux/x86-64, Linux/x32 and Linux/i686 as well as with
build-many-glibcs.py.
---
 csu/gmon-start.c              | 10 +++++++++-
 gmon/tst-gmon-gprof.sh        |  2 ++
 gmon/tst-gmon-static-gprof.sh |  2 ++
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/csu/gmon-start.c b/csu/gmon-start.c
index b3432885b3..344606a676 100644
--- a/csu/gmon-start.c
+++ b/csu/gmon-start.c
@@ -52,6 +52,11 @@ extern char ENTRY_POINT[];
 #endif
 extern char etext[];
 
+/* Use __executable_start as the lowest address to keep profiling records
+   if it provided by the linker.  */
+extern const char executable_start[] asm ("__executable_start")
+  __attribute__ ((weak, visibility ("hidden")));
+
 #ifndef TEXT_START
 # ifdef ENTRY_POINT_DECL
 #  define TEXT_START ENTRY_POINT
@@ -92,7 +97,10 @@ __gmon_start__ (void)
   called = 1;
 
   /* Start keeping profiling records.  */
-  __monstartup ((u_long) TEXT_START, (u_long) &etext);
+  if (&executable_start != NULL)
+    __monstartup ((u_long) &executable_start, (u_long) &etext);
+  else
+    __monstartup ((u_long) TEXT_START, (u_long) &etext);
 
   /* Call _mcleanup before exiting; it will write out gmon.out from the
      collected data.  */
diff --git a/gmon/tst-gmon-gprof.sh b/gmon/tst-gmon-gprof.sh
index 9d371582b9..dc0be02110 100644
--- a/gmon/tst-gmon-gprof.sh
+++ b/gmon/tst-gmon-gprof.sh
@@ -39,12 +39,14 @@ trap cleanup 0
 cat > "$expected" <<EOF
 f1 2000
 f2 1000
+f3 1
 EOF
 
 # Special version for powerpc with function descriptors.
 cat > "$expected_dot" <<EOF
 .f1 2000
 .f2 1000
+.f3 1
 EOF
 
 "$GPROF" -C "$program" "$data" \
diff --git a/gmon/tst-gmon-static-gprof.sh b/gmon/tst-gmon-static-gprof.sh
index 79218df967..4cc99c80d0 100644
--- a/gmon/tst-gmon-static-gprof.sh
+++ b/gmon/tst-gmon-static-gprof.sh
@@ -39,6 +39,7 @@ trap cleanup 0
 cat > "$expected" <<EOF
 f1 2000
 f2 1000
+f3 1
 main 1
 EOF
 
@@ -46,6 +47,7 @@ EOF
 cat > "$expected_dot" <<EOF
 .f1 2000
 .f2 1000
+.f3 1
 .main 1
 EOF
 
-- 
2.31.1