ftrace/recordmcount: mcount address adjustment

Introduce mcount_adjust{,_32,_64} to the C implementation of
recordmcount analog to $mcount_adjust in the perl script.
The adjustment is added to the address of the relocations
against the mcount symbol. If this adjustment is done by
recordmcount at compile time the ftrace_call_adjust function
can be turned into a nop.

Cc: John Reiser <jreiser@bitwagon.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 7 insertions, 2 deletions

diff --git a/scripts/recordmcount.h b/scripts/recordmcount.h
index 3c00faba745..4be60364a40 100644
--- a/scripts/recordmcount.h
+++ b/scripts/recordmcount.h
@@ -22,6 +22,7 @@
 #undef is_fake_mcount
 #undef fn_is_fake_mcount
 #undef MIPS_is_fake_mcount
+#undef mcount_adjust
 #undef sift_rel_mcount
 #undef nop_mcount
 #undef find_secsym_ndx
@@ -63,6 +64,7 @@
 # define is_fake_mcount         is_fake_mcount64
 # define fn_is_fake_mcount      fn_is_fake_mcount64
 # define MIPS_is_fake_mcount    MIPS64_is_fake_mcount
+# define mcount_adjust          mcount_adjust_64
 # define Elf_Addr               Elf64_Addr
 # define Elf_Ehdr               Elf64_Ehdr
 # define Elf_Shdr               Elf64_Shdr
@@ -94,6 +96,7 @@
 # define is_fake_mcount         is_fake_mcount32
 # define fn_is_fake_mcount      fn_is_fake_mcount32
 # define MIPS_is_fake_mcount    MIPS32_is_fake_mcount
+# define mcount_adjust          mcount_adjust_32
 # define Elf_Addr               Elf32_Addr
 # define Elf_Ehdr               Elf32_Ehdr
 # define Elf_Shdr               Elf32_Shdr
@@ -132,6 +135,8 @@ static void fn_ELF_R_INFO(Elf_Rel *const rp, unsigned sym, unsigned type)
 }
 static void (*Elf_r_info)(Elf_Rel *const rp, unsigned sym, unsigned type) = fn_ELF_R_INFO;
 
+static int mcount_adjust = 0;
+
 /*
  * MIPS mcount long call has 2 _mcount symbols, only the position of the 1st
  * _mcount symbol is needed for dynamic function tracer, with it, to disable
@@ -317,8 +322,8 @@ static uint_t *sift_rel_mcount(uint_t *mlocp,
                         mcountsym = get_mcountsym(sym0, relp, str0);
 
                 if (mcountsym == Elf_r_sym(relp) && !is_fake_mcount(relp)) {
-                        uint_t const addend = _w(_w(relp->r_offset) - recval);
-
+                        uint_t const addend =
+                                _w(_w(relp->r_offset) - recval + mcount_adjust);
                         mrelp->r_offset = _w(offbase
                                 + ((void *)mlocp - (void *)mloc0));
                         Elf_r_info(mrelp, recsym, reltype);