[SLOF] [PATCH] libc: The arguments of puts() can be marked as "const"

[Alexey Kardashevskiy]

On 09/06/17 03:13, Segher Boessenkool wrote:
> On Thu, Jun 08, 2017 at 08:54:06AM +0200, Thomas Huth wrote:
>> On 08.06.2017 08:12, Alexey Kardashevskiy wrote:
>>> /home/aik/p/slof/slof/paflof.c: In function ‘engine’:
>>> /home/aik/p/slof/slof/paflof.c:84:23: warning: array subscript is below
>>> array bounds [-Warray-bounds]
>>>    dp = the_data_stack - 1;
>>>         ~~~~~~~~~~~~~~~^~~
>>> /home/aik/p/slof/slof/paflof.c:85:22: warning: array subscript is below
>>> array bounds [-Warray-bounds]
>>>    rp = handler_stack - 1;
>>>         ~~~~~~~~~~~~~~^~~
>>>
>>> with gcc (GCC) 6.3.1 20161221 (Red Hat 6.3.1-1) from Fedora24/BE.
>>>
>>> Can you please take a look on this? Thanks.
>>
>> See Segher's suggestions here:
>>
>>  https://lists.ozlabs.org/pipermail/slof/2016-August/001221.html
>>
>> IMHO we could also just simply sacrifice the first stack entry and only
>> use "dp = the_data_stack", without adding the inline asm here (to keep
>> paflof.c portable).
> 
> Or you simply make the_*_stack declared as a pointer in paflof.c, not as
> an array.  Where is it actually defined?  If it is defined in assembler
> code all is fine; if it is defined in C code, well, don't lie to the
> compiler or it will take its revenge (if using full-program optimisation
> it can still see you're accessing the array out-of-bounds for example,
> or worse, assume you don't do undefined things and optimise accordingly).


slof/paflof.c includes slof/ppc64.c (via #include ISTR(TARG,c)) which
defines the_data_stack.

handler_stack is defined right in slof/paflof.c's engine().

> An easy way around is to have the_*_stack just an external symbol, and
> have the_real_*_stack for the arrays of cells, and then equate the two
> in a linker script.

Harsh.

> Or, ignore the warning.  If ever things break (and they won't), it will
> do so with lots of fireworks; it won't silently break.

This shuts the gcc up (and we loose 1 cell in each stack):


diff --git a/slof/paflof.c b/slof/paflof.c
index 50b4adf..1e7874a 100644
--- a/slof/paflof.c
+++ b/slof/paflof.c
@@ -68,7 +68,8 @@ long engine(int mode, long param_1, long param_2)

        cell *restrict ip;
        cell *restrict cfa;
-       static cell handler_stack[160];
+       static cell handler_stack_[160];
+       static cell *handler_stack = handler_stack_ + 1;
        static cell c_return[2];
        static cell dummy;

diff --git a/slof/ppc64.c b/slof/ppc64.c
index 83a8e82..76c1bdf 100644
--- a/slof/ppc64.c
+++ b/slof/ppc64.c
@@ -26,7 +26,8 @@ cell the_exception_frame[0x400 / CELLSIZE] __attribute__
((aligned(PAGE_SIZE)));
 cell the_client_frame[0x1000 / CELLSIZE] __attribute__ ((aligned(0x100)));
 cell the_client_stack[0x8000 / CELLSIZE] __attribute__ ((aligned(0x100)));
 /* THE forth stack */
-cell the_data_stack[0x2000 / CELLSIZE] __attribute__ ((aligned(0x100)));
+cell the_data_stack_[0x2000 / CELLSIZE] __attribute__ ((aligned(0x100)));
+cell *the_data_stack = the_data_stack_ + 1;
 /* the forth return stack */
 cell the_return_stack[0x2000 / CELLSIZE] __attribute__ ((aligned(0x100)));



-- 
Alexey