module: Ignore RISC-V mapping symbols too

RISC-V has an extended form of mapping symbols that we use to encode
the ISA when it changes in the middle of an ELF. This trips up modpost
as a build failure, I haven't yet verified it yet but I believe the
kallsyms difference should result in stacks looking sane again.

Reported-by: Randy Dunlap <[e-mail]>
Closes: https://lore.kernel.org/all/[e-mail]/
Signed-off-by: Palmer Dabbelt <[e-mail]>
Reviewed-by: Randy Dunlap <[e-mail]>
Tested-by: Randy Dunlap <[e-mail]> # build-tested
Signed-off-by: Luis Chamberlain <[e-mail]>

include/linux/module_symbol.h

···
 #define _LINUX_MODULE_SYMBOL_H
 
 /* This ignores the intensely annoying "mapping symbols" found in ELF files. */
-static inline int is_mapping_symbol(const char *str)
+static inline int is_mapping_symbol(const char *str, int is_riscv)
 {
 	if (str[0] == '.' && str[1] == 'L')
 		return true;
 	if (str[0] == 'L' && str[1] == '0')
 		return true;
+	/*
+	 * RISC-V defines various special symbols that start with "$".  The
+	 * mapping symbols, which exist to differentiate between incompatible
+	 * instruction encodings when disassembling, show up all over the place
+	 * and are generally not meant to be treated like other symbols.  So
+	 * just ignore any of the special symbols.
+	 */
+	if (is_riscv)
+		return str[0] == '$';
+
 	return str[0] == '$' &&
 	       (str[1] == 'a' || str[1] == 'd' || str[1] == 't' || str[1] == 'x')
 	       && (str[2] == '\0' || str[2] == '.');

kernel/module/kallsyms.c

···
 		 * and inserted at a whim.
 		 */
 		if (*kallsyms_symbol_name(kallsyms, i) == '\0' ||
-		    is_mapping_symbol(kallsyms_symbol_name(kallsyms, i)))
+		    is_mapping_symbol(kallsyms_symbol_name(kallsyms, i), IS_ENABLED(CONFIG_RISCV)))
 			continue;
 
 		if (thisval <= addr && thisval > bestval) {

scripts/mod/modpost.c

···
 
 	if (!name || !strlen(name))
 		return 0;
-	return !is_mapping_symbol(name);
+	return !is_mapping_symbol(name, elf->hdr->e_machine == EM_RISCV);
 }
 
 /* Look up the nearest symbol based on the section and the address */