On 6/14/18 11:00 AM, Arnaldo Carvalho de Melo wrote:
Em Thu, Jun 14, 2018 at 02:47:59PM -0300, Arnaldo Carvalho de Melo escreveu:
Em Thu, Jun 14, 2018 at 10:21:30AM -0700, Alexei Starovoitov escreveu:
On 6/14/18 10:18 AM, Arnaldo Carvalho de Melo wrote:
Just out of curiosity, is there any plan to have this as a clang option?
I think
clang ... -mllvm -mattr=dwarfris
should work.
The message "(LLVM option parsing)" implies what you suggest, but didn't
worked :-\
-mllvm <value> Additional arguments to forward to LLVM's option
processing
Almost there tho :-\
So I thought that this -mattr=dwarfris would be available only after I
set the target, because I tried 'llc -mattr=help' and dwarfris wasn't
there:
[acme@jouet perf]$ llc -mattr=help |& grep dwarf
[acme@jouet perf]$
Only after I set the arch it appears:
[acme@jouet perf]$ llc -march=bpf -mattr=help |& grep dwarf
dwarfris - Disable MCAsmInfo DwarfUsesRelocationsAcrossSections.
dwarfris - Disable MCAsmInfo DwarfUsesRelocationsAcrossSections.
dwarfris - Disable MCAsmInfo DwarfUsesRelocationsAcrossSections.
[acme@jouet perf]$
But even after moving the '-mllvm -mattr=dwarfris' to after '-target
bpf' it still can't grok it :-\
/usr/local/bin/clang -D__KERNEL__ -D__NR_CPUS__=4 -DLINUX_VERSION_CODE=0x41100
-g -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/7/include
-I/home/acme/git/linux/arch/x86/include -I./arch/x86/include/generated
-I/home/acme/git/linux/include -I./include
-I/home/acme/git/linux/arch/x86/include/uapi
-I./arch/x86/include/generated/uapi -I/home/acme/git/linux/include/uapi
-I./include/generated/uapi -include
/home/acme/git/linux/include/linux/kconfig.h -I/home/acme/lib/include/perf/bpf
-Wno-unused-value -Wno-pointer-sign -working-directory
/lib/modules/4.17.0-rc5/build -c /home/acme/bpf/hello.c -target bpf -mllvm
-mattr=dwarfris -O2 -o hello.o
So onlye with 'clang ... -target bpf -emit-llvm -O2 -o - | llc -march=bpf
-mattr=dwarfris ...'
things work as we expect.
Right. Currently, the only way to use option -mattr=dwarfris is through
llc. The "clang -mllvm -mattr=dwarfris" won't work since
-mllvm <value> Additional arguments to forward to LLVM's option
processing
and -mattr=dwarfris is not in LLVM auto option processing system.
Those options, in llvm source code, typically have a pattern like below:
===
static cl::opt<unsigned> MemCmpEqZeroNumLoadsPerBlock(
"memcmp-num-loads-per-block", cl::Hidden, cl::init(1),
cl::desc("The number of loads per basic block for inline expansion of "
"memcmp that is only being compared against zero."));
===
I really want to get rid of this option as well. To make pahole work
with the default default format, I need to add bpf support to
libdwfl in elfutils repo. I will work on that.
- Arnaldo
