LLVM will not allocate storage for the "foo" in "static const int foo = 1". Instead it inlines the value at the use sites, and emits a DW_TAG_variable with DW_AT_const_value for the definition of "foo". GCC will allocate storage for both at -O0 but at -O2 the same problem exists. Unfortunately, partial debug info (PDI) instances without a location don't get added to the psymtabs table. That means that if you do the following: cat <<EOF > one.c static const int one = 1; extern int fetch_two (void); int main (int argc, char *argv[]) { return one + fetch_two (); } EOF cat <<EOF > two.c static const int two = 2; int fetch_two (void) { return two; } EOF gcc -g -O2 -c -o one.o one.c gcc -g -O2 -c -o two.o two.c gcc -g -o test one.o two.o gdb ./test Then at the GDB prompt: (gdb) p one $1 = 1 (gdb) p two No symbol "two" in current context. The reason we can get "one" and not "two" is because the symtab for one.c has been expanded, when we went to look for main. If we expand the compilation unit for two.c and flush the symbol cache, if on GDB trunk: (gdb) mt expand foo.c # only needed on trunk (gdb) mt flush-symbol-cache (gdb) print two $2 = 2 The ultimate cause is that dwarf2read.c:add_partial_symbol punts if the symbol has no location, thinking it's a declaration and not a definition. Well if it has a DT_AT_const_value, it might be a definition too. Patch coming tomorrow.
The master branch has been updated by Andy Wingo <wingo@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=ff908ebf8612a737d9e168eca0604ff6c97556bc commit ff908ebf8612a737d9e168eca0604ff6c97556bc Author: Andy Wingo <wingo@igalia.com> Date: Thu Mar 26 19:41:15 2015 +0100 Properly intern constants into psymtab Variables with a DW_AT_const_value but without a DW_AT_location were not getting added to the partial symbol table. They are added to the full symbol table, however, when the compilation unit's psymtabs are expanded. Before: (gdb) p one No symbol "one" in current context. (gdb) mt flush-symbol-cache (gdb) mt expand one.c (gdb) p one $1 = 1 After: (gdb) p one $1 = 1 To the user it's pretty strange, as depending on whether tab completion has forced expansion of all CUs or not the lookup might succeed, or not if the failure was already added to the symbol cache. This commit simply makes sure to add constants to the partial symbol tables. gdb/testsuite/ChangeLog: PR symtab/18148 * gdb.dwarf2/dw2-intercu.S (one, two): Add variables that have a const_value but not a location. * gdb.dwarf2/dw2-intercu.exp: Add tests that constants without location defined in non-main CUs are visible. gdb/ChangeLog: PR symtab/18148 * dwarf2read.c (struct partial_die_info): Add has_const_value member. (add_partial_symbol): Don't punt on symbols that have const_value attributes. (read_partial_die): Detect DW_AT_const_value.
Patch committed.