Re: [PATCH] gas: Fix internal error in S_SET_SEGMENT

[Alex Coplan <alex.coplan@arm.com>]

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Hi H.J,

Sorry for the delay; just got back from some time off.

> -----Original Message-----
> From: H.J. Lu <hjl.tools@gmail.com>
> Sent: 22 July 2020 15:40
> To: Alex Coplan <Alex.Coplan@arm.com>
> Cc: Binutils <binutils@sourceware.org>
> Subject: Re: [PATCH] gas: Fix internal error in S_SET_SEGMENT
> 
> > gas/ChangeLog:
> >
> > 2020-07-22  Alex Coplan  <alex.coplan@arm.com>
> >
> >         * config/obj-elf.c (obj_elf_change_section): When
> >         repurposing an existing symbol, ensure that we set sy_value as
> >         per other (fresh) section symbols.
> >         * testsuite/gas/aarch64/section-symbol-redef.d: New test.
> >         * testsuite/gas/aarch64/section-symbol-redef.s: Input for test.
> >
> 
> Why are tests arm specific?  Can you put them to ELF tests?

Thanks for pointing this out. I wasn't sure if there was a
suitably-generic place for these to go, but it seems that the ELF test
directory is the right place.

See the updated patch attached. The test has been tweaked to fix the
indentation for targets that assume anything in the first column is a
label, and to skip on targets that either don't support assignment
(bfin) or require attributes for sections (h8300).

Is the updated version OK for master?

Thanks,
Alex

---

gas/ChangeLog:

2020-08-03  Alex Coplan  <alex.coplan@arm.com>

	* config/obj-elf.c (obj_elf_change_section): When repurposing an
	existing symbol, ensure that we set sy_value as per other (fresh)
	section symbols.
	* testsuite/gas/elf/elf.exp: Add new test.
	* testsuite/gas/elf/section-symbol-redef.d: New test.
	* testsuite/gas/elf/section-symbol-redef.s: Input for test.


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diff --git a/gas/config/obj-elf.c b/gas/config/obj-elf.c
index de22b5a1da8..c11a1da2295 100644
--- a/gas/config/obj-elf.c
+++ b/gas/config/obj-elf.c
@@ -759,7 +759,14 @@ obj_elf_change_section (const char *name,
       /* Add a symbol for this section to the symbol table.  */
       secsym = symbol_find (name);
       if (secsym != NULL)
-	symbol_set_bfdsym (secsym, sec->symbol);
+	{
+	  /* We could be repurposing an undefined symbol here: make sure we
+	     reset sy_value to look like other section symbols in order to avoid
+	     trying to incorrectly resolve this section symbol later on.  */
+	  static const expressionS expr = { .X_op = O_constant };
+	  symbol_set_value_expression (secsym, &expr);
+	  symbol_set_bfdsym (secsym, sec->symbol);
+	}
       else
 	symbol_table_insert (section_symbol (sec));
     }
diff --git a/gas/testsuite/gas/elf/elf.exp b/gas/testsuite/gas/elf/elf.exp
index 86b304ae34f..8cd61b36754 100644
--- a/gas/testsuite/gas/elf/elf.exp
+++ b/gas/testsuite/gas/elf/elf.exp
@@ -303,6 +303,7 @@ if { [is_elf_format] } then {
     run_dump_test "strtab"
 
     run_dump_test "bignums"
+    run_dump_test "section-symbol-redef"
     
     load_lib gas-dg.exp
     dg-init
diff --git a/gas/testsuite/gas/elf/section-symbol-redef.d b/gas/testsuite/gas/elf/section-symbol-redef.d
new file mode 100644
index 00000000000..88807a196a7
--- /dev/null
+++ b/gas/testsuite/gas/elf/section-symbol-redef.d
@@ -0,0 +1,6 @@
+#readelf: -x myseg
+#skip: bfin-*-*
+#skip: h8300-*
+
+Hex dump of section .*:
+  0x0+ 2a\s+\*
diff --git a/gas/testsuite/gas/elf/section-symbol-redef.s b/gas/testsuite/gas/elf/section-symbol-redef.s
new file mode 100644
index 00000000000..87e65699b48
--- /dev/null
+++ b/gas/testsuite/gas/elf/section-symbol-redef.s
@@ -0,0 +1,3 @@
+  myseg=not_defined_here
+  .section myseg
+  .byte 42