ftrace/recordmcount: Avoid STT_FUNC symbols as base on ARM

While find_secsym_ndx often finds the unamed local STT_SECTION, if a
section has only one function in it, the ARM toolchain generates the
STT_FUNC symbol before the STT_SECTION, and recordmcount finds this
instead.

This is problematic on ARM because in ARM ELFs, "if a [STT_FUNC] symbol
addresses a Thumb instruction, its value is the address of the
instruction with bit zero set (in a relocatable object, the section
offset with bit zero set)".  This leads to incorrect mcount addresses
being recorded.

Fix this by not using STT_FUNC symbols as the base on ARM.

Signed-off-by: Rabin Vincent <rabin@rab.in>
Link: http://lkml.kernel.org/r/1305134631-31617-1-git-send-email-rabin@rab.in
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/scripts/recordmcount.h b/scripts/recordmcount.h
index 4be60364a40..f40a6af6bf4 100644
--- a/scripts/recordmcount.h
+++ b/scripts/recordmcount.h
@@ -43,6 +43,7 @@
 #undef ELF_R_INFO
 #undef Elf_r_info
 #undef ELF_ST_BIND
+#undef ELF_ST_TYPE
 #undef fn_ELF_R_SYM
 #undef fn_ELF_R_INFO
 #undef uint_t
@@ -76,6 +77,7 @@
 # define ELF_R_INFO             ELF64_R_INFO
 # define Elf_r_info             Elf64_r_info
 # define ELF_ST_BIND            ELF64_ST_BIND
+# define ELF_ST_TYPE            ELF64_ST_TYPE
 # define fn_ELF_R_SYM           fn_ELF64_R_SYM
 # define fn_ELF_R_INFO          fn_ELF64_R_INFO
 # define uint_t                 uint64_t
@@ -108,6 +110,7 @@
 # define ELF_R_INFO             ELF32_R_INFO
 # define Elf_r_info             Elf32_r_info
 # define ELF_ST_BIND            ELF32_ST_BIND
+# define ELF_ST_TYPE            ELF32_ST_TYPE
 # define fn_ELF_R_SYM           fn_ELF32_R_SYM
 # define fn_ELF_R_INFO          fn_ELF32_R_INFO
 # define uint_t                 uint32_t
@@ -427,6 +430,11 @@ static unsigned find_secsym_ndx(unsigned const txtndx,
                 if (txtndx == w2(symp->st_shndx)
                         /* avoid STB_WEAK */
                     && (STB_LOCAL == st_bind || STB_GLOBAL == st_bind)) {
+                        /* function symbols on ARM have quirks, avoid them */
+                        if (w2(ehdr->e_machine) == EM_ARM
+                            && ELF_ST_TYPE(symp->st_info) == STT_FUNC)
+                                continue;
+
                         *recvalp = _w(symp->st_value);
                         return symp - sym0;
                 }