[PATCH] module: Ignore RISC-V mapping symbols too

[Palmer Dabbelt]

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 <rdunlap at infradead.org>
Link: https://lore.kernel.org/all/9d9e2902-5489-4bf0-d9cb-556c8e5d71c2@infradead.org/
Signed-off-by: Palmer Dabbelt <palmer at rivosinc.com>
---
I'm not sure about a fixes here, the breakage comes from a binutils change
that's pretty much independent from the kernel.

Plumbing in through the RISC-V-specific switch is also a bit ugly, but I'm not
sure just dropping everyone's "$"-prefixed symbols is a good idea -- the rest
of this is sort of half-way arch-specific, though, so maybe that's the way to
go?  I figure it's easier to delete stuff than add it, though.
---
 include/linux/module_symbol.h | 12 +++++++++++-
 kernel/module/kallsyms.c      |  8 +++++++-
 scripts/mod/modpost.c         |  2 +-
 3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/include/linux/module_symbol.h b/include/linux/module_symbol.h
index 7ace7ba30203..5b799942b243 100644
--- a/include/linux/module_symbol.h
+++ b/include/linux/module_symbol.h
@@ -3,12 +3,22 @@
 #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] == '.');
diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
index ef73ae7c8909..1e988e542c5d 100644
--- a/kernel/module/kallsyms.c
+++ b/kernel/module/kallsyms.c
@@ -12,6 +12,12 @@
 #include <linux/bsearch.h>
 #include "internal.h"
 
+#ifdef CONFIG_RISCV
+#define IS_RISCV 1
+#else
+#define IS_RISCV 0
+#endif
+
 /* Lookup exported symbol in given range of kernel_symbols */
 static const struct kernel_symbol *lookup_exported_symbol(const char *name,
 							  const struct kernel_symbol *start,
@@ -289,7 +295,7 @@ static const char *find_kallsyms_symbol(struct module *mod,
 		 * 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_RISCV))
 			continue;
 
 		if (thisval <= addr && thisval > bestval) {
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index b29b29707f10..7c71429d6502 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1052,7 +1052,7 @@ static inline int is_valid_name(struct elf_info *elf, Elf_Sym *sym)
 
 	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 */
-- 
2.41.0