Messages in this thread Patch in this message | | | Date | Sun, 6 Dec 2020 09:36:16 +0000 (GMT) | From | "Maciej W. Rozycki" <> | Subject | Re: [PATCH] mips: lib: uncached: fix uninitialized variable 'sp' |
| |
On Fri, 27 Nov 2020, Anders Roxell wrote:
> When building mips tinyconfig with clang the following warning show up: > > /tmp/arch/mips/lib/uncached.c:40:18: note: initialize the variable 'sp' to silence this warning > register long sp __asm__("$sp"); > ^ > = 0 > > Rework to make an explicit inline move.
It's not uninitialised, because by definition $sp has been initialised. This code wouldn't have worked for the last 15 years otherwise.
It is however non-standard usage (which may not have been clarified at the time this piece was made; I recall extensive discussions around this feature over the years):
"6.47.5.2 Specifying Registers for Local Variables ................................................. [...]
"The only supported use for this feature is to specify registers for input and output operands when calling Extended 'asm' (*note Extended Asm::). [...]"
so the change description should refer to that as the rationale rather than an implementation-specific misleading warning (although that can be quoted for a reference of course).
> diff --git a/arch/mips/lib/uncached.c b/arch/mips/lib/uncached.c > index 09d5deea747f..21a4b94a0558 100644 > --- a/arch/mips/lib/uncached.c > +++ b/arch/mips/lib/uncached.c > @@ -37,10 +37,11 @@ > */ > unsigned long run_uncached(void *func) > { > - register long sp __asm__("$sp"); > register long ret __asm__("$2"); > long lfunc = (long)func, ufunc; > long usp; > + long sp; > + asm ("move %0, $sp" : "=r" (sp));
Missing newline between the variable block and code here; you may well swap it with the empty line below you have left. Also use `__asm__' for consistency, and remove the extraneous space ahead of the parenthesis as we don't use them in Linux. Using a tab to separate the mnemonic from operands is also preferable, i.e. "move\t%0, $sp" in this case (using actual tabs works better with multi-line assembly, but this is not one).
I think this should be OK once the issues I mentioned here have been addressed.
Maciej
| |