On 21/12/2022 16.05, Geert Uytterhoeven wrote:
Hi Günter,
On Wed, Dec 21, 2022 at 3:54 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
On Wed, Oct 19, 2022 at 02:30:34PM -0600, Jason A. Donenfeld wrote:
Recently, some compile-time checking I added to the clamp_t family of
functions triggered a build error when a poorly written driver was
compiled on ARM, because the driver assumed that the naked `char` type
is signed, but ARM treats it as unsigned, and the C standard says it's
architecture-dependent.
I doubt this particular driver is the only instance in which
unsuspecting authors make assumptions about `char` with no `signed` or
`unsigned` specifier. We were lucky enough this time that that driver
used `clamp_t(char, negative_value, positive_value)`, so the new
checking code found it, and I've sent a patch to fix it, but there are
likely other places lurking that won't be so easily unearthed.
So let's just eliminate this particular variety of heisensign bugs
entirely. Set `-funsigned-char` globally, so that gcc makes the type
unsigned on all architectures.
This will break things in some places and fix things in others, so this
will likely cause a bit of churn while reconciling the type misuse.
There is an interesting fallout: When running the m68k:q800 qemu emulation,
there are lots of warning backtraces.
WARNING: CPU: 0 PID: 23 at crypto/testmgr.c:5724 alg_test.part.0+0x7c/0x326
testmgr: alg_test_descs entries in wrong order: 'adiantum(xchacha12,aes)' before 'adiantum(xchacha20,aes)'
------------[ cut here ]------------
WARNING: CPU: 0 PID: 23 at crypto/testmgr.c:5724 alg_test.part.0+0x7c/0x326
testmgr: alg_test_descs entries in wrong order: 'adiantum(xchacha20,aes)' before 'aegis128'
and so on for pretty much every entry in the alg_test_descs[] array.
Bisect points to this patch, and reverting it fixes the problem.
It looks like the problem is that arch/m68k/include/asm/string.h
uses "char res" to store the result of strcmp(), and char is now
unsigned - meaning strcmp() will now never return a value < 0.
Effectively that means that strcmp() is broken on m68k if
CONFIG_COLDFIRE=n.
The fix is probably quite simple.
diff --git a/arch/m68k/include/asm/string.h b/arch/m68k/include/asm/string.h
index f759d944c449..b8f4ae19e8f6 100644
--- a/arch/m68k/include/asm/string.h
+++ b/arch/m68k/include/asm/string.h
@@ -42,7 +42,7 @@ static inline char *strncpy(char *dest, const char *src, size_t n)
#define __HAVE_ARCH_STRCMP
static inline int strcmp(const char *cs, const char *ct)
{
- char res;
+ signed char res;
asm ("\n"
"1: move.b (%0)+,%2\n" /* get *cs */
Does that make sense ? If so I can send a patch.
Thanks, been there, done that
https://lore.kernel.org/all/bce014e60d7b1a3d1c60009fc3572e2f72591f21.1671110959.git.geert@xxxxxxxxxxxxxx
Well, looks like that would still leave strcmp() buggy, you can't
represent all possible differences between two char values (signed or
not) in an 8-bit quantity. So any implementation based on returning the
first non-zero value of *a - *b must store that intermediate value in
something wider. Otherwise you'll get -128 from strcmp("\x40", "\xc0"),
but _also_ -128 when you do strcmp("\xc0", "\x40"), which is obviously
bogus.
I recently fixed that long-standing bug in U-Boot's strcmp() and a
similar one in nolibc in the linux tree. I wonder how many more
instances exist.
Rasmus
