[PATCH v2 2/2] gdb: Fix reduce/reduce conflicts for qualifier_seq_noopt in the C parser.

[Felix Willgerodt]

This fixes a problem with GDB's address space qualifier parsing.  GDB uses
'@' as a way to express an address space in expression evaluation.  This can
currently lead to a crash for "Add support for the __flash qualifier on AVR"
(487d975399dfcb2bb2f0998a7d12bd62acdd9fa1)
, the only user I am aware of.

Program:
~~~
const __flash char data_in_flash = 0xab;

int
main (void)
{
  const __flash char *pointer_to_flash = &data_in_flash;
}
~~~

Before:
~~~
(gdb) p data_in_flash
$1 = -85 '\253'
(gdb) p *(const char * @flash) pointer_to_flash
$2 = -85 '\253'
(gdb) p *(@flash const char *) pointer_to_flash
type-stack.c:201: internal-error: type* type_stack::follow_types(type*): unrecognized tp_ value in follow_types
A problem internal to GDB has been detected,
further debugging may prove unreliable.
Quit this debugging session? (y or n)
~~~

After:
~~~
(gdb) p data_in_flash
$1 = -85 '\253'
(gdb) p *(const char *) pointer_to_flash
$2 = 0 '\000'
(gdb) p *(const char * @flash) pointer_to_flash
$3 = -85 '\253'
(gdb) p *(@flash const char *) pointer_to_flash
$4 = 0 '\000'
(gdb)
~~~

Note that how the binding of this qualifier is interpreted and resolved for an
address/pointer is target specific.  Hence only the prepended qualifier works
for AVR, even if it seems syntactically incorrect.  I won't change this for
AVR, as I am not familiar with that target.

Bison now also complains about less conflicts:

Before:
  YACC   c-exp.c
gdb/gdb/c-exp.y: warning: 153 shift/reduce conflicts [-Wconflicts-sr]
gdb/gdb/c-exp.y: warning: 70 reduce/reduce conflicts [-Wconflicts-rr]

After:
  YACC   c-exp.c
gdb/gdb/c-exp.y: warning: 60 shift/reduce conflicts [-Wconflicts-sr]
gdb/gdb/c-exp.y: warning: 69 reduce/reduce conflicts [-Wconflicts-rr]

gdb/ChangeLog:
2021-03-22  Felix Willgerodt  <felix.willgerodt@intel.com>

	* c-exp.y (qualifier_seq_noopt): Replace qualifier_seq with
	qualifier_seq_noopt.
---
 gdb/c-exp.y | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gdb/c-exp.y b/gdb/c-exp.y
index d3232fb25bc..36607e2eee1 100644
--- a/gdb/c-exp.y
+++ b/gdb/c-exp.y
@@ -1275,7 +1275,7 @@ single_qualifier:
 
 qualifier_seq_noopt:
 		single_qualifier
-	| 	qualifier_seq single_qualifier
+	| 	qualifier_seq_noopt single_qualifier
 	;
 
 qualifier_seq:
-- 
2.25.4

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