[PATCH v2] libgcc/mkmap-symver: support skip_underscore (PR74748)

[Waldemar Brodkorb <wbx at openadk dot org>]

Hi,

Some platforms, such as Blackfin, have a special prefix for assembly
symbols as opposed to C symbols. For this reason, a function named
"foo()" in C will in fact be visible as a symbol called "_foo" in the
ELF binary.

The current linker version script logic in libgcc doesn't take into
account this situation properly. The Blackfin specific
libgcc/config/bfin/libgcc-glibc.ver has an additional "_" in front of
every symbol so that it matches the output of "nm" (which gets parsed to
produce the final linker version script). But due to this additional
"_", ld no longer matches with the symbols since "ld" does the matching
with the original symbol name, not the one prefixed with "_".

Due to this, none of the symbols in libgcc/config/bfin/libgcc-glibc.ver
are actually matched with symbols in libgcc. This causes all libgcc
symbols to be left as "LOCAL", which causes lots of "undefined
reference" whenever some C or C++ code that calls a function of libgcc
is compiled.

To address this, this commit introduces a "skip_underscore" variable to
the mkmap-symver script. It tells mkmap-symver to ignore the leading
underscore from the "nm" output.

Note that this new argument is different from the existing
"leading_underscore" argument, which *adds* an additional underscore to
the generated linker version script.

Having this functionality paves the way to using the generic linker
version information for Blackfin, instead of using a custom one.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Waldemar Brodkorb <wbx@openadk.org>

2016-11-26  Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

	PR gcc/74748
	* libgcc/mkmap-symver.awk: add support for skip_underscore


diff --git a/libgcc/mkmap-symver.awk b/libgcc/mkmap-symver.awk
index 266832a..0a57d31 100644
--- a/libgcc/mkmap-symver.awk
+++ b/libgcc/mkmap-symver.awk
@@ -47,7 +47,11 @@ state == "nm" && ($1 == "U" || $2 == "U") {
 
 state == "nm" && NF == 3 {
   split ($3, s, "@")
-  def[s[1]] = 1;
+  if (skip_underscore && substr(s[1], 1, 1) == "_")
+      symname = substr(s[1], 2);
+  else
+      symname = s[1];
+  def[symname] = 1;
   sawsymbol = 1;
   next;
 }

Thanks in advance,
 Waldemar