On Mon, Mar 14, 2022 at 12:16:16PM +0800, Michael Chang wrote: > On Fri, Mar 11, 2022 at 12:35:57AM +0100, Daniel Kiper wrote: > > Latest GCC may complain in that way: > > > > commands/i386/pc/sendkey.c: In function ‘grub_sendkey_postboot’: > > commands/i386/pc/sendkey.c:223:21: error: writing 1 byte into a region of > > size 0 [-Werror=stringop-overflow=] > > 223 | *((char *) 0x41a) = 0x1e; > > | ~~~~~~~~~~~~~~~~~~^~~~~~ > > > > The volatile keyword addition helps and additionally assures us the > > compiler will not optimize out fixed assignments. > > > > Signed-off-by: Daniel Kiper <daniel.ki...@oracle.com> > > --- > > grub-core/commands/i386/pc/sendkey.c | 8 ++++---- > > 1 file changed, 4 insertions(+), 4 deletions(-) > > > > diff --git a/grub-core/commands/i386/pc/sendkey.c > > b/grub-core/commands/i386/pc/sendkey.c > > index 26d9acd3d..ab4bca9e9 100644 > > --- a/grub-core/commands/i386/pc/sendkey.c > > +++ b/grub-core/commands/i386/pc/sendkey.c > > @@ -220,8 +220,8 @@ grub_sendkey_postboot (void) > > > > *flags = oldflags; > > > > - *((char *) 0x41a) = 0x1e; > > - *((char *) 0x41c) = 0x1e; > > + *((volatile char *) 0x41a) = 0x1e; > > + *((volatile char *) 0x41c) = 0x1e; > > > > return GRUB_ERR_NONE; > > } > > @@ -236,8 +236,8 @@ grub_sendkey_preboot (int noret __attribute__ > > ((unused))) > > oldflags = *flags; > > > > /* Set the sendkey. */ > > - *((char *) 0x41a) = 0x1e; > > - *((char *) 0x41c) = keylen + 0x1e; > > + *((volatile char *) 0x41a) = 0x1e; > > + *((volatile char *) 0x41c) = keylen + 0x1e; > > grub_memcpy ((char *) 0x41e, sendkey, 0x20); > > > > /* Transform "any ctrl" to "right ctrl" flag. */ > > -- > > 2.11.0 > > Unfortunately the volatile keyword doesn't help on a more recent gcc-12 > build [1]. With that -Warray-bounds warning [2] is emitted this time > than -Wstringop-overflow.
Ugh... Though I have taken the patch because it at least fix the problem partially. > I believe this is caused by this gcc regression in which hardwired > literal address is treated as NULL plus an offset, while there's no good > way to tell that literal address being an invalid accesses at non-zero > offsets to null pointers or not: > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578 > > Before upstream comes up with a solution or introducing new annotation > for literal pointer. For the time being their recommedation is to > suppress the warning with #pragma or use volatile pointer which appears > to not work for gcc-12. > > Instead of inserting #pragma all over the places to avoid the diagnose > of Warray-bounds. I think we can try to port absolute_pointer [3] and > RELOC_HIDE [4] used by the linux kernel to disconnect a pointer using > literal address from its original object hence gcc won't make > assumptions on the boundary while doing pointer arithmetic. This sounds > a better way to go as it can work across gcc versions. > > I am halfway in preparing the patch to wrap literal pointers in > absolute_pointer. Before posting it here, I'd like to know do we have > any other prefernece like just disabling it via #pragma as that sounds > more like a norm? I think absolute_pointer() looks like a better solution. Thank you for taking a stab at this. Daniel _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org https://lists.gnu.org/mailman/listinfo/grub-devel
