Patchwork [2/4] Handle copy relocations

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Submitter Tom Tromey
Date July 30, 2019, 9 p.m.
Message ID <87d0hrkzl3.fsf@tromey.com>
Download mbox | patch
Permalink /patch/33862/
State New
Headers show

Comments

Tom Tromey - July 30, 2019, 9 p.m.
Pedro> To be more correct, this depends on ABI, or how you compile your
Pedro> binary.  Compiling the main binary as PIC/PIE may or may not use
Pedro> copy relocations and use GOT accesses instead, for example.

Yes, thanks for mentioning that.

Pedro> I'm surprised to find no tests in this patch?

The existing Ada exception-catching tests cover this, so I didn't add a
new test.

Pedro>  FAIL: gdb.base/print-file-var.exp: hidden=1: dlopen=0: version_id_main=0: 'print-file-var-lib2.c'::this_version_id == v2

I haven't investigated the other failures yet, but I think this one in
particular is an existing bug in c-exp.y.  What happens is that this
does not actually look up the symbol from that source file!  Instead it
finds the symbol in print-file-var-lib1.c.

Pedro> But I'm wondering whether fixing the hidden=1 cases would fit
Pedro> with the design of your patch, or does that scenario require
Pedro> thinking about all this differently?

I think applying the appended probably makes sense.  This rules out
symbols where the corresponding minsym is hidden.

Tom
Tom Tromey - July 30, 2019, 9:28 p.m.
Tom> I haven't investigated the other failures yet, but I think this one in
Tom> particular is an existing bug in c-exp.y.  What happens is that this
Tom> does not actually look up the symbol from that source file!  Instead it
Tom> finds the symbol in print-file-var-lib1.c.

Digging a bit deeper, the culprit seems to be lookup_global_symbol.
I think this function should respect a block that's passed in.

However, this code also calls
gdbarch_iterate_over_objfiles_in_search_order and solib_global_lookup,
and now I wonder if one or both of these needs to be changed
as well.

For example, if stopped in the library, "print this_version_id" should
probably follow the expected-by-the-library-author lookup, but currently
I think will not.

Maybe windows_iterate_over_objfiles_in_search_order should just be the
default.  I am not sure.

Tom
Tom Tromey - July 31, 2019, 7:21 p.m.
Tom> Digging a bit deeper, the culprit seems to be lookup_global_symbol.
Tom> I think this function should respect a block that's passed in.

I managed to get the new test completely passing.

I changed basic_lookup_symbol_nonlocal to search the block's global
block, and I removed the long comments fro 2002-3 about why this isn't
done.  TBH I think all of that was just mistaken.

This change got to just 2 failures.  The last two were both the
"hidden0...main0" variants, which print:

get_version_1: &this_version_id=0x7ffff7fca010, this_version_id=104
get_version_2: &this_version_id=0x7ffff7fca010, this_version_id=104

So, I think for these the answer is to change the new get_symbol_address
to search all objfiles in order.  I'm slightly unhappy with this but it
seems correct enough.

I'm re-testing the series and will resubmit it once that's done,
assuming there aren't regressions.

thanks,
Tom

Patch

diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index f81efb4f433..90dfde0f1e9 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -21653,11 +21653,19 @@  new_symbol (struct die_info *die, struct type *type, struct dwarf2_cu *cu,
 	      else if (attr2 && (DW_UNSND (attr2) != 0))
 		{
 		  if (SYMBOL_CLASS (sym) == LOC_STATIC
-		      && (objfile->flags & OBJF_MAINLINE) == 0)
+		      && (objfile->flags & OBJF_MAINLINE) == 0
+		      && dwarf2_per_objfile->can_copy)
 		    {
 		      /* A global static variable might be subject to
-			 copy relocation.  */
-		      sym->maybe_copied = dwarf2_per_objfile->can_copy;
+			 copy relocation.  We first check for a local
+			 minsym, though, because maybe the symbol was
+			 marked hidden, in which case this would not
+			 apply.  */
+		      minimal_symbol *found
+			= (lookup_minimal_symbol_linkage
+			   (SYMBOL_LINKAGE_NAME (sym), objfile));
+		      if (found != nullptr)
+			sym->maybe_copied = 1;
 		    }
 
 		  /* A variable with DW_AT_external is never static,