Re: [PATCH] perf riscv: fix register name strings

[Martin Kaiser <martin@kaiser.cx>]

Thus wrote Arnaldo Carvalho de Melo (acme@kernel.org):

> On Mon, Jun 08, 2026 at 05:27:03PM -0300, Arnaldo Carvalho de Melo wrote:
> > On Mon, Jun 08, 2026 at 01:08:28PM -0700, Ian Rogers wrote:
> > > On Mon, Jun 8, 2026 at 12:27 PM Martin Kaiser <martin@kaiser.cx> wrote:

> > > > On risc-v, pref probe generates an invalid syntax for a named register in
> > > > a kprobe.

> > > > $ perf probe --debug verbose --add "n_tty_write tty"
> > > > ...
> > > > Writing event: p:probe/n_tty_write _text+8922528 tty=%"%a0":x64
> > > > Failed to write event: Invalid argument

> > > > The problem is the combination of

> > > >    #define REG_DWARFNUM_NAME(reg, idx) [idx] = "%" #reg

> > > > and entries such as

> > > >    REG_DWARFNUM_NAME("%a0", 10)

> > > > where #reg will escape the quotes of the first macro parameter.

> > > > Update the macro definition to produce the correct syntax for a named
> > > > register in a kprobe, i.e. the unquoted register name with only one
> > > > leading %.

> > > > Fixes: a90c4519186d ("perf riscv: Remove dwarf-regs.c and add dwarf-regs-table.h")
> > > > Signed-off-by: Martin Kaiser <martin@kaiser.cx>

> > > Reviewed-by: Ian Rogers <irogers@google.com>

> > > Thanks for catching this! Sashiko is also green for this change:
> > > https://sashiko.dev/#/patchset/20260608192731.708606-1-martin%40kaiser.cx

> > Strange,

> >   LD      /tmp/build/perf-tools-next/tests/perf-test-in.o
> >   LD      /tmp/build/perf-tools-next/perf-test-in.o
> > In file included from util/dwarf-regs.c:23:
> > util/../arch/riscv/include/dwarf-regs-table.h:5:9: error: ‘REG_DWARFNUM_NAME’ redefined [-Werror]
> >     5 | #define REG_DWARFNUM_NAME(reg, idx)     [idx] = reg
> >       |         ^~~~~~~~~~~~~~~~~
> > In file included from util/dwarf-regs.c:22:
> > util/../arch/powerpc/include/dwarf-regs-table.h:10:9: note: this is the location of the previous definition
> >    10 | #define REG_DWARFNUM_NAME(reg, idx)     [idx] = "%" #reg
> >       |         ^~~~~~~~~~~~~~~~~
> > In file included from util/dwarf-regs.c:24:
> > util/../arch/s390/include/dwarf-regs-table.h:5:9: error: ‘REG_DWARFNUM_NAME’ redefined [-Werror]
> >     5 | #define REG_DWARFNUM_NAME(reg, idx)     [idx] = "%" #reg
> >       |         ^~~~~~~~~~~~~~~~~
> > util/../arch/riscv/include/dwarf-regs-table.h:5:9: note: this is the location of the previous definition
> >     5 | #define REG_DWARFNUM_NAME(reg, idx)     [idx] = reg
> >       |         ^~~~~~~~~~~~~~~~~
> > cc1: all warnings being treated as errors
> > make[4]: *** [/home/acme/git/perf-tools-next/tools/build/Makefile.build:96: /tmp/build/perf-tools-next/util/dwarf-regs.o] Error 1


> > Trying to figure out why Sashiko is green on it but it doesn't build
> > here...

> C preprocessor benign redefinition rule kicked in, this is a preexisting
> problem, the headers need to undef that REG_DWARFNUM_NAME that now is
> different in one of the headers, Risc-V's.

> I'll cook up a patch to merge before this one.

I see. We need an undef for risc-v, similar to mips.

Let me send a v2 so we have all in one patch, that should be simpler to
backport to stable.

Thanks,
Martin