[binutils-gdb] gdb: Fix reduce/reduce conflicts for qualifier_seq_noopt in the C parser.

[binutils-gdb] gdb: Fix reduce/reduce conflicts for qualifier_seq_noopt in the C parser.

[Felix Willgerodt]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=184dcd81c7972c3fd3557ec4a04064529ee3ca8d

commit 184dcd81c7972c3fd3557ec4a04064529ee3ca8d
Author: Felix Willgerodt <felix.willgerodt@intel.com>
Date:   Tue Apr 20 08:44:17 2021 +0200

    gdb: Fix reduce/reduce conflicts for qualifier_seq_noopt in the C parser.
    
    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:
    2021-04-20  Felix Willgerodt  <felix.willgerodt@intel.com>
    
            * c-exp.y (qualifier_seq_noopt): Replace qualifier_seq with
            qualifier_seq_noopt.

Diff:
---
 gdb/ChangeLog | 5 +++++
 gdb/c-exp.y   | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 8692c0f8c43..a601300e955 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2021-04-20  Felix Willgerodt  <felix.willgerodt@intel.com>
+
+	* c-exp.y (qualifier_seq_noopt): Replace qualifier_seq with
+	qualifier_seq_noopt.
+
 2021-04-20  Felix Willgerodt  <felix.willgerodt@intel.com>
 
 	* c-exp.y (single_qualifier): Handle UNKNOWN_CPP_NAME.
diff --git a/gdb/c-exp.y b/gdb/c-exp.y
index 3e416f4e2c7..93b10f05b7d 100644
--- a/gdb/c-exp.y
+++ b/gdb/c-exp.y
@@ -1276,7 +1276,7 @@ single_qualifier:
 
 qualifier_seq_noopt:
 		single_qualifier
-	| 	qualifier_seq single_qualifier
+	| 	qualifier_seq_noopt single_qualifier
 	;
 
 qualifier_seq: