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When compiling a project using -frepo, .rpo files are written alongside
the .o file, the symbols either have O or C against them. During final linking,
the objects can be recompiled with some of the entries tweaked/chosen by the
tlink.c code (visible with TLINK_VERBOSE=3), it does this by changing O -> C
in the .rpo files.
My tests showed that init_repo (cp/repo.c) was correctly calling
IDENTIFIER_REPO_CHOSEN against the right identifers and setting the
chosen bit.
By the time finish_repo() or emit_repo_p() were called, the pointer returned
by get_identifier() for the symbol marked during init_repo had changed and
the chosen bit was no longer set. This lead to linking bugs like:
collect: relinking
collect2: error: '_ZNK6sudoku5ClearINS_8SequenceEEclERS1_' was assigned to 'board.rpo', but was not defined during recompilation, or vice versa
The problem is that the garbage collection is getting called before
finish_repo() is called and ggc_protect_identifiers is set to false
so the identifiers are not preserved. They are recreated but the
chosen bits get wiped out which is why the pointer changes and the
chosen bit is not set.
The fix is to change ggc_protect_identifiers *after* the finish_repo
calls are made.
Reproduction is tricky since you need to trigger the garbage collector at
just the right moment.
RP 2013/10/9
[YOCTO #5133]
Upstream-Status: Pending
Index: gcc-4.8.1/gcc/toplev.c
===================================================================
--- gcc-4.8.1.orig/gcc/toplev.c 2013-03-28 08:29:51.000000000 +0000
+++ gcc-4.8.1/gcc/toplev.c 2013-10-09 20:27:17.089228023 +0000
@@ -551,11 +551,11 @@
if (flag_syntax_only || flag_wpa)
return;
- ggc_protect_identifiers = false;
-
/* This must also call finalize_compilation_unit. */
lang_hooks.decls.final_write_globals ();
+ ggc_protect_identifiers = false;
+
if (seen_error ())
return;
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