perf symbols: Ignore mapping symbols on riscv

RISCV ELF use mapping symbols with special names $x, $d to
identify regions of RISCV code or code with different ISAs[1].
These symbols don't identify functions, so will confuse the
perf output.

The patch filters out these symbols at load time, similar to
"4886f2ca perf symbols: Ignore mapping symbols on aarch64".

[1] https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/
    master/riscv-elf.adoc#mapping-symbol

Signed-off-by: Haibo Xu <[email protected]>
Acked-by: Namhyung Kim <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexandre Ghiti <[email protected]>
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: xiaobo55x

tools/perf/util/symbol-elf.c

@@ -1733,6 +1733,12 @@ dso__load_sym_internal(struct dso *dso, struct map *map, struct symsrc *syms_ss,
 				continue;
 		}
 
+		/* Reject RISCV ELF "mapping symbols" */
+		if (ehdr.e_machine == EM_RISCV) {
+			if (elf_name[0] == '$' && strchr("dx", elf_name[1]))
+				continue;
+		}
+
 		if (runtime_ss->opdsec && sym.st_shndx == runtime_ss->opdidx) {
 			u32 offset = sym.st_value - syms_ss->opdshdr.sh_addr;
 			u64 *opd = opddata->d_buf + offset;