gforth and gcc 4.7

[Andrew Haley]

On 03/26/2012 05:46 PM, Jakub Jelinek wrote:
> On Mon, Mar 26, 2012 at 04:54:05PM +0200, Adrian Reber wrote:
>> Trying to build gforth with gcc 4.7 fails currently. The forth engine is
>> build but it fails its included tests. The problem is that every newline
>> the forth engine writes is replaced with 0x00 as seen in following diff:
>>
>>  0000010: 6566 696e 6564 2047 4458 2020 594f 5520  efined GDX  YOU 
>>  0000020: 5348 4f55 4c44 2053 4545 2054 4845 2053  SHOULD SEE THE S
>>  0000030: 5441 4e44 4152 4420 4752 4150 4849 4320  TANDARD GRAPHIC 
>> -0000040: 4348 4152 4143 5445 5253 3a00 2021 2223  CHARACTERS:. !"#
>>                                      ^^ actual output
>> +0000040: 4348 4152 4143 5445 5253 3a0a 2021 2223  CHARACTERS:. !"#
>>                                      ^^ expected output
>>  0000050: 2425 2627 2829 2a2b 2c2d 2e2f 3031 3233  $%&'()*+,-./0123
>>
>> Removing -O2 from the compiler commandline fixes it, but I have no idea
>> why this happens. Does anyone have an idea how this can be solved?
> 
> If -O0 works and -O2 doesn't, first narrow it down using a binary search
> between -O0 and -O2 compiled objects to at least a single compilation
> unit, then you could use __attribute__((optimize (0))) (resp.
> __attribute__((optimize (2))) ) and/or -fno-inline to narrow it even
> further, read the problematic code, see if there aren't any e.g. aliasing
> warnings (-O2 enables -fstrict-aliasing), if you don't spot a bug in the
> gforth code after this and still suspect the compiler, turn that into
> self-contained minimal testcase (for the problematic routine add main
> that calls it with the right arguments, make the problematic
> routine __attribute__((noinline, noclone)) and stub out anything it calls,
> then file a gcc bugreport?

It's this bug, which returns the address of a local array:

diff -r f14bc589172e prim
--- a/prim      Thu Apr 12 14:42:46 2012 +0100
+++ b/prim      Thu Apr 12 14:51:21 2012 +0100
@@ -1950,7 +1950,7 @@

 newline        ( -- c_addr u ) gforth
 ""String containing the newline sequence of the host OS""
-char newline[] = {
+static const char newline[] = {
 #if DIRSEP=='/'
 /* Unix */
 '\n'

We might as well also fix this other bug, which prevents the disassembler from
working:

diff -r f14bc589172e dis-gdb.fs
--- a/dis-gdb.fs        Thu Apr 12 14:42:46 2012 +0100
+++ b/dis-gdb.fs        Thu Apr 12 14:51:21 2012 +0100
@@ -25,7 +25,7 @@
 : disasm-gdb { addr u -- }
     base @ >r hex
     s\" type mktemp >/dev/null && type gdb >/dev/null && file=`mktemp -t gforthdis.XXXXXXXXXX` && file2=`mktemp -t gforthdis.XXXXXXXXXX` && echo \"set verbose off\nset logging file $file\nset logging on\ndisas " save-mem ( addr u addr1 u1 )
-    addr 0 <<# bl hold # #s 'x hold # #> append-extend-string #>>
+    addr 0 <<# bl hold ',' hold # #s 'x hold # #> append-extend-string #>>
     addr u + 0 <<# # #s 'x hold # #> append-extend-string #>>
     r> base ! cr
     s\" \nset logging off\nquit\n\" >$file2 && gdb -nx -q -p `ps -p $$ -o ppid=` -x $file2 2>/dev/null >/dev/null && rm $file2 && grep -v \"of assembler\" $file && rm $file" append-extend-string

Andrew.