Hi Rasmus,
On 9/30/24 11:54 AM, Rasmus Villemoes wrote:
Quentin Schulz <quentin.sch...@cherry.de> writes:
Hi Rasmus,
On 9/27/24 8:56 PM, Rasmus Villemoes wrote:
Quentin Schulz <foss+ub...@0leil.net> writes:
From: Quentin Schulz <quentin.sch...@cherry.de>
My linter complains that "When using void pointers in calculations, the
behaviour is undefined".
GCC does say that "In GNU C, addition and subtraction operations are
supported on pointers to void"[1] but this hints at this only being
supported in the GNU flavor of C. And I assume U-Boot may want to be
compiled with clang/llvm?
Let's fix that warning by casting the void pointer to a u8 pointer since
the size variable unit is byte.
[1] https://gcc.gnu.org/onlinedocs/gcc/Pointer-Arith.html
No, let's please not. Try enabling -Wpointer-arith and see how much
churn that would require all over the tree (doing it in this one place
would be pointless), and all the casts would make the code much much
harder to read.
That alone is not a justification.
We do rely on lots of gcc extensions, and Clang has documented that it
"aims to support a broad range of GCC extensions". Arithmetic on void is
one of them, and that's not going to go away.
But this very well could/is.
1) is there a way to tell Clang that we want to follow this GNU
extension for that case?
For that case? No. But we do -std=gnu11 which is understood by both
compilers and tells clang that we do use GNU extensions. I don't know
the clang internals, but I strongly suspect that that flag would make
sure that defaults for various warnings are set appropriately (that is,
not warning for something which is explicitly guaranteed to work in GNU
C).
Is that the default?
In our build, yes. See CSTD_FLAG. But both gcc and clang default to some
-std=gnuXX, with the exact value of XX depending on compiler version.
2) do we document somewhere the GNU C extensions we use on the whole
tree?
Not that I know of explicitly, but CSTD_FLAG=-std=gnu11 kind of
documents that gnu extensions are used.
Note that typeof() and inline asm() statements are also gnu extensions
that we make heavy use of, as are various __attribute__(()), statement
expressions (i.e. ({ stuff; }) ), omitting the middle expression in ?: ,
special handling of token paste ## after a comma, case ranges 'case LOW
... HIGH', etc. etc.
Ack, thanks for the info!
3) is anyone aware of a way to silence some specific warnings at the
project level so that clang takes care of it so that linters use those
settings so we avoid people sending more commits for that "issue"?
I don't quite parse that sentence. Are you saying that your linter is
being invoked by clang, and you want clang to pass certain options to
the linter to disable certain warnings? I don't know how clang could
know that options those would be.
My understanding is that my linter is calling clang. So I thought it
would be a nice thing to have a way to specify options for clang at the
root of the project so that any linter "wrapping" clang would use those
options and not warn/error on things we don't want to check.
I spent 5min looking for it and it seems we already have that:
https://docs.u-boot.org/en/latest/build/gen_compile_commands.html
After running that script, my linter is happy.
Thanks!
Cheers,
Quentin
