| Message ID | 20201211102437.3929348-1-anders.roxell@linaro.org (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 5b058973d3205578aa6c9a71392e072a11ca44ef |
| Headers | show |
| Series | [v2] mips: lib: uncached: fix non-standard usage of variable 'sp' | expand |
On Fri, Dec 11, 2020 at 2:24 AM Anders Roxell <anders.roxell@linaro.org> wrote: > > When building mips tinyconfig with clang the following warning show up: > > arch/mips/lib/uncached.c:45:6: warning: variable 'sp' is uninitialized when used here [-Wuninitialized] > if (sp >= (long)CKSEG0 && sp < (long)CKSEG2) > ^~ > arch/mips/lib/uncached.c:40:18: note: initialize the variable 'sp' to silence this warning > register long sp __asm__("$sp"); > ^ > = 0 > 1 warning generated. > > Rework to make an explicit inline move, instead of the non-standard use > of specifying registers for local variables. This is what's written > from the gcc-10 manual [1] about specifying registers for local > variables: > > "6.47.5.2 Specifying Registers for Local Variables > ................................................. > [...] > > "The only supported use for this feature is to specify registers for > input and output operands when calling Extended 'asm' (*note Extended > Asm::). [...]". > > [1] https://docs.w3cub.com/gcc~10/local-register-variables > Signed-off-by: Anders Roxell <anders.roxell@linaro.org> Link: https://github.com/ClangBuiltLinux/linux/issues/606 Reported-by: Nathan Chancellor <natechancellor@gmail.com> Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> > --- > arch/mips/lib/uncached.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/arch/mips/lib/uncached.c b/arch/mips/lib/uncached.c > index 09d5deea747f..f80a67c092b6 100644 > --- a/arch/mips/lib/uncached.c > +++ b/arch/mips/lib/uncached.c > @@ -37,10 +37,12 @@ > */ > unsigned long run_uncached(void *func) > { > - register long sp __asm__("$sp"); > register long ret __asm__("$2"); > long lfunc = (long)func, ufunc; > long usp; > + long sp; > + > + __asm__("move %0, $sp" : "=r" (sp)); > > if (sp >= (long)CKSEG0 && sp < (long)CKSEG2) > usp = CKSEG1ADDR(sp); > -- > 2.29.2 >
On Fri, 11 Dec 2020, Anders Roxell wrote: > diff --git a/arch/mips/lib/uncached.c b/arch/mips/lib/uncached.c > index 09d5deea747f..f80a67c092b6 100644 > --- a/arch/mips/lib/uncached.c > +++ b/arch/mips/lib/uncached.c > @@ -37,10 +37,12 @@ > */ > unsigned long run_uncached(void *func) > { > - register long sp __asm__("$sp"); > register long ret __asm__("$2"); > long lfunc = (long)func, ufunc; > long usp; > + long sp; > + > + __asm__("move %0, $sp" : "=r" (sp)); I thought it might be better to make `sp' global instead, so that it's the compiler that chooses how to schedule accesses. Have you tried that? Maciej
On Fri, Dec 11, 2020 at 07:54:07PM +0000, Maciej W. Rozycki wrote: > On Fri, 11 Dec 2020, Anders Roxell wrote: > > > diff --git a/arch/mips/lib/uncached.c b/arch/mips/lib/uncached.c > > index 09d5deea747f..f80a67c092b6 100644 > > --- a/arch/mips/lib/uncached.c > > +++ b/arch/mips/lib/uncached.c > > @@ -37,10 +37,12 @@ > > */ > > unsigned long run_uncached(void *func) > > { > > - register long sp __asm__("$sp"); > > register long ret __asm__("$2"); > > long lfunc = (long)func, ufunc; > > long usp; > > + long sp; > > + > > + __asm__("move %0, $sp" : "=r" (sp)); > > I thought it might be better to make `sp' global instead, so that it's > the compiler that chooses how to schedule accesses. Have you tried that? > > Maciej This will not work, as the LLVM Mips backend does not support using $sp as a global register variable: https://github.com/llvm/llvm-project/commit/1440bb2a26ff13df1b29762658ee122cc0bc47ae $ make -skj"$(nproc)" ARCH=mips CROSS_COMPILE=mipsel-linux-gnu- LLVM=1 O=out \ distclean malta_kvm_guest_defconfig vmlinux fatal error: error in backend: Invalid register name global variable ... Cheers, Nathan
On Fri, Dec 11, 2020 at 11:24:37AM +0100, Anders Roxell wrote: > When building mips tinyconfig with clang the following warning show up: > > arch/mips/lib/uncached.c:45:6: warning: variable 'sp' is uninitialized when used here [-Wuninitialized] > if (sp >= (long)CKSEG0 && sp < (long)CKSEG2) > ^~ > arch/mips/lib/uncached.c:40:18: note: initialize the variable 'sp' to silence this warning > register long sp __asm__("$sp"); > ^ > = 0 > 1 warning generated. > > Rework to make an explicit inline move, instead of the non-standard use > of specifying registers for local variables. This is what's written > from the gcc-10 manual [1] about specifying registers for local > variables: > > "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::). [...]". > > [1] https://docs.w3cub.com/gcc~10/local-register-variables > Signed-off-by: Anders Roxell <anders.roxell@linaro.org> > --- > arch/mips/lib/uncached.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) applied to mips-next. Thomas.
On Mon, 14 Dec 2020 at 21:05, Thomas Bogendoerfer <tsbogend@alpha.franken.de> wrote: > > On Fri, Dec 11, 2020 at 11:24:37AM +0100, Anders Roxell wrote: > > When building mips tinyconfig with clang the following warning show up: > > > > arch/mips/lib/uncached.c:45:6: warning: variable 'sp' is uninitialized when used here [-Wuninitialized] > > if (sp >= (long)CKSEG0 && sp < (long)CKSEG2) > > ^~ > > arch/mips/lib/uncached.c:40:18: note: initialize the variable 'sp' to silence this warning > > register long sp __asm__("$sp"); > > ^ > > = 0 > > 1 warning generated. <trimp> > > [1] https://docs.w3cub.com/gcc~10/local-register-variables > > Signed-off-by: Anders Roxell <anders.roxell@linaro.org> > > --- > > arch/mips/lib/uncached.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > applied to mips-next. We have noticed these build failures on stable tree also. May I request you to initiate the process to get into the stable tree and for the following branches. - linux-5.10.y - linux-5.9.y - linux-5.4.y - linux-4.19.y - Naresh
diff --git a/arch/mips/lib/uncached.c b/arch/mips/lib/uncached.c index 09d5deea747f..f80a67c092b6 100644 --- a/arch/mips/lib/uncached.c +++ b/arch/mips/lib/uncached.c @@ -37,10 +37,12 @@ */ unsigned long run_uncached(void *func) { - register long sp __asm__("$sp"); register long ret __asm__("$2"); long lfunc = (long)func, ufunc; long usp; + long sp; + + __asm__("move %0, $sp" : "=r" (sp)); if (sp >= (long)CKSEG0 && sp < (long)CKSEG2) usp = CKSEG1ADDR(sp);
When building mips tinyconfig with clang the following warning show up: arch/mips/lib/uncached.c:45:6: warning: variable 'sp' is uninitialized when used here [-Wuninitialized] if (sp >= (long)CKSEG0 && sp < (long)CKSEG2) ^~ arch/mips/lib/uncached.c:40:18: note: initialize the variable 'sp' to silence this warning register long sp __asm__("$sp"); ^ = 0 1 warning generated. Rework to make an explicit inline move, instead of the non-standard use of specifying registers for local variables. This is what's written from the gcc-10 manual [1] about specifying registers for local variables: "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::). [...]". [1] https://docs.w3cub.com/gcc~10/local-register-variables Signed-off-by: Anders Roxell <anders.roxell@linaro.org> --- arch/mips/lib/uncached.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)