Subject: Re: [RFC -next] linux/linkage.h: fix symbol prefix handling

From: Rusty Russell <[email-masked]>
Date: Wed, 13 Mar 2013 10:30:16 +1030

Stephen Rothwell <[email-masked]> writes:

> Hi Rusty,
>
> Looks partly better.   You seem to be using
> CONFIG_SYMBOL_PREFIX_UNDERSCORE but selecting
> CONFIG_HAVE_UNDERSCORE_SYMBOL_PREFIX.  One trivial comment below.
>
> Maybe this was an unfinished version of the patch?

Indeed.  It was crap.... now I've applied James' copious fixes, and
actually, y'know, proof-read it.

This is what I'll push into my fixes/ branch now, and if it survives a
day in linux-next, will push to Linus.

Thanks,
Rusty.

v2: Rename CONFIG_SYMBOL_PREFIX_UNDERSCORE to
    CONFIG_HAVE_UNDERSCORE_SYMBOL_PREFIX, which is defined in
    arch/Kconfig and selected by the 3 archs which need it.

v3: Clean up remnants of v1, s/VMLINUX_SYMBOL_NAME/VMLINUX_SYMBOL_STR/
    in description, note that Al's commit is in linux-next only,
    remove whitespace-only hunk.

CONFIG_SYMBOL_PREFIX: cleanup.

We have CONFIG_SYMBOL_PREFIX, which three archs define to the string
"_".  But Al Viro broke this in "consolidate cond_syscall and
SYSCALL_ALIAS declarations" (in linux-next), and he's not the first to
do so.

Using CONFIG_SYMBOL_PREFIX is awkward, since we usually just want to
prefix it so something.  So various places define helpers which are
defined to nothing if CONFIG_SYMBOL_PREFIX isn't set:

1) include/asm-generic/unistd.h defines __SYMBOL_PREFIX.
2) include/asm-generic/vmlinux.lds.h defines VMLINUX_SYMBOL(sym)
3) include/linux/export.h defines MODULE_SYMBOL_PREFIX.
4) include/linux/kernel.h defines SYMBOL_PREFIX (which differs from #7)
5) kernel/modsign_certificate.S defines ASM_SYMBOL(sym)
6) scripts/modpost.c defines MODULE_SYMBOL_PREFIX
7) scripts/Makefile.lib defines SYMBOL_PREFIX on the commandline if
   CONFIG_SYMBOL_PREFIX is set, so that we have a non-string version
   for pasting.

(arch/h8300/include/asm/linkage.h defines SYMBOL_NAME(), too).

Let's solve this properly:
1) No more generic prefix, just CONFIG_HAVE_UNDERSCORE_SYMBOL_PREFIX.
2) Make linux/export.h usable from asm.
3) Define VMLINUX_SYMBOL, VMLINUX_SYMBOL_STR and VMLINUX_SYMBOL_PREFIX_STR.
4) Make everyone use them.

Signed-off-by: Rusty Russell <[email-masked]>
Reviewed-by: James Hogan <[email-masked]>
Tested-by: James Hogan <[email-masked]> (on metag)

diff --git a/Makefile b/Makefile
index a05ea42..10fb6c7 100644
--- a/Makefile
+++ b/Makefile
@@ -1398,7 +1398,7 @@ quiet_cmd_rmfiles = $(if $(wildcard $(rm-files)),CLEAN   $(wildcard $(rm-files))
 # Run depmod only if we have System.map and depmod is executable
 quiet_cmd_depmod = DEPMOD  $(KERNELRELEASE)
       cmd_depmod = $(CONFIG_SHELL) $(srctree)/scripts/depmod.sh $(DEPMOD) \
-                   $(KERNELRELEASE) "$(patsubst "%",%,$(CONFIG_SYMBOL_PREFIX))"
+                   $(KERNELRELEASE) "$(patsubst y,_,$(CONFIG_HAVE_SYMBOL_PREFIX_UNDERSCORE))"
 
 # Create temporary dir for module support files
 # clean it up only when building all modules
diff --git a/arch/Kconfig b/arch/Kconfig
index 5a1779c..12ba8f9 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -391,6 +391,12 @@ config MODULES_USE_ELF_REL
 	  Modules only use ELF REL relocations.  Modules with ELF RELA
 	  relocations will give an error.
 
+config HAVE_UNDERSCORE_SYMBOL_PREFIX
+	bool
+	help
+	  Some architectures generate an _ in front of C symbols; things like
+	  module loading and assembly files need to know about this.
+
 #
 # ABI hall of shame
 #
diff --git a/arch/blackfin/Kconfig b/arch/blackfin/Kconfig
index 600494c..314ee6a 100644
--- a/arch/blackfin/Kconfig
+++ b/arch/blackfin/Kconfig
@@ -1,7 +1,3 @@
-config SYMBOL_PREFIX
-	string
-	default "_"
-
 config MMU
 	def_bool n
 
@@ -33,6 +29,7 @@ config BLACKFIN
 	select ARCH_HAVE_CUSTOM_GPIO_H
 	select ARCH_WANT_OPTIONAL_GPIOLIB
 	select HAVE_UID16
+	select HAVE_UNDERSCORE_SYMBOL_PREFIX
 	select HAVE_VIRT_TO_BUS
 	select ARCH_WANT_IPC_PARSE_VERSION
 	select HAVE_GENERIC_HARDIRQS
diff --git a/arch/h8300/Kconfig b/arch/h8300/Kconfig
index ae8551e..2333cf6 100644
--- a/arch/h8300/Kconfig
+++ b/arch/h8300/Kconfig
@@ -12,10 +12,7 @@ config H8300
 	select MODULES_USE_ELF_RELA
 	select OLD_SIGSUSPEND3
 	select OLD_SIGACTION
-
-config SYMBOL_PREFIX
-	string
-	default "_"
+	select HAVE_UNDERSCORE_SYMBOL_PREFIX
 
 config MMU
 	bool
diff --git a/arch/metag/Kconfig b/arch/metag/Kconfig
index afc8973..2099617 100644
--- a/arch/metag/Kconfig
+++ b/arch/metag/Kconfig
@@ -1,7 +1,3 @@
-config SYMBOL_PREFIX
-	string
-	default "_"
-
 config METAG
 	def_bool y
 	select EMBEDDED
@@ -27,6 +23,7 @@ config METAG
 	select HAVE_MOD_ARCH_SPECIFIC
 	select HAVE_PERF_EVENTS
 	select HAVE_SYSCALL_TRACEPOINTS
+	select HAVE_UNDERSCORE_SYMBOL_PREFIX
 	select IRQ_DOMAIN
 	select MODULES_USE_ELF_RELA
 	select OF
diff --git a/drivers/mtd/chips/gen_probe.c b/drivers/mtd/chips/gen_probe.c
index 3b9a284..00d20ad 100644
--- a/drivers/mtd/chips/gen_probe.c
+++ b/drivers/mtd/chips/gen_probe.c
@@ -204,14 +204,14 @@ static inline struct mtd_info *cfi_cmdset_unknown(struct map_info *map,
 	struct cfi_private *cfi = map->fldrv_priv;
 	__u16 type = primary?cfi->cfiq->P_ID:cfi->cfiq->A_ID;
 #ifdef CONFIG_MODULES
-	char probename[16+sizeof(MODULE_SYMBOL_PREFIX)];
+	char probename[16+sizeof(VMLINUX_SYMBOL_PREFIX_STR)];
 	cfi_cmdset_fn_t *probe_function;
 
-	sprintf(probename, MODULE_SYMBOL_PREFIX "cfi_cmdset_%4.4X", type);
+	sprintf(probename, VMLINUX_SYMBOL_PREFIX_STR "cfi_cmdset_%4.4X", type);
 
 	probe_function = __symbol_get(probename);
 	if (!probe_function) {
-		request_module(probename + sizeof(MODULE_SYMBOL_PREFIX) - 1);
+		request_module(probename + sizeof(VMLINUX_SYMBOL_PREFIX_STR)-1);
 		probe_function = __symbol_get(probename);
 	}
 
diff --git a/include/asm-generic/unistd.h b/include/asm-generic/unistd.h
index 4077b5d..15c0598 100644
--- a/include/asm-generic/unistd.h
+++ b/include/asm-generic/unistd.h
@@ -1,4 +1,5 @@
 #include <uapi/asm-generic/unistd.h>
+#include <linux/export.h>
 
 /*
  * These are required system calls, we should
@@ -17,12 +18,7 @@
  * but it doesn't work on all toolchains, so we just do it by hand
  */
 #ifndef cond_syscall
-#ifdef CONFIG_SYMBOL_PREFIX
-#define __SYMBOL_PREFIX CONFIG_SYMBOL_PREFIX
-#else
-#define __SYMBOL_PREFIX
-#endif
-#define cond_syscall(x) asm(".weak\t" __SYMBOL_PREFIX #x "\n\t" \
-			    ".set\t" __SYMBOL_PREFIX #x "," \
-			    __SYMBOL_PREFIX "sys_ni_syscall")
+#define cond_syscall(x) asm(".weak\t" VMLINUX_SYMBOL_STR(x) "\n\t"	\
+			    ".set\t" VMLINUX_SYMBOL_STR(x) ","	\
+			    VMLINUX_SYMBOL_STR(sys_ni_syscall))
 #endif
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index afa12c7..eb58d2d 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -52,13 +52,7 @@
 #define LOAD_OFFSET 0
 #endif
 
-#ifndef SYMBOL_PREFIX
-#define VMLINUX_SYMBOL(sym) sym
-#else
-#define PASTE2(x,y) x##y
-#define PASTE(x,y) PASTE2(x,y)
-#define VMLINUX_SYMBOL(sym) PASTE(SYMBOL_PREFIX, sym)
-#endif
+#include <linux/export.h>
 
 /* Align . to a 8 byte boundary equals to maximum function alignment. */
 #define ALIGN_FUNCTION()  . = ALIGN(8)
diff --git a/include/linux/export.h b/include/linux/export.h
index 696c0f4..fc83b2a 100644
--- a/include/linux/export.h
+++ b/include/linux/export.h
@@ -7,15 +7,27 @@
  *
  * If you feel the need to add #include <linux/foo.h> to this file
  * then you are doing something wrong and should go away silently.
+ *
+ * If you think the above arrogance just encourages more people to add
+ * random crap to this file, you're not alone.
  */
 
 /* Some toolchains use a `_' prefix for all user symbols. */
-#ifdef CONFIG_SYMBOL_PREFIX
-#define MODULE_SYMBOL_PREFIX CONFIG_SYMBOL_PREFIX
+#ifdef CONFIG_HAVE_UNDERSCORE_SYMBOL_PREFIX
+#define __VMLINUX_SYMBOL(x) _##x
+#define __VMLINUX_SYMBOL_STR(x) "_" #x
+#define VMLINUX_SYMBOL_PREFIX_STR "_"
 #else
-#define MODULE_SYMBOL_PREFIX ""
+#define __VMLINUX_SYMBOL(x) x
+#define __VMLINUX_SYMBOL_STR(x) #x
+#define VMLINUX_SYMBOL_PREFIX_STR ""
 #endif
 
+/* Indirect, so macros are expanded before pasting. */
+#define VMLINUX_SYMBOL(x) __VMLINUX_SYMBOL(x)
+#define VMLINUX_SYMBOL_STR(x) __VMLINUX_SYMBOL_STR(x)
+
+#ifndef __ASSEMBLY__
 struct kernel_symbol
 {
 	unsigned long value;
@@ -51,7 +63,7 @@ extern struct module __this_module;
 	__CRC_SYMBOL(sym, sec)					\
 	static const char __kstrtab_##sym[]			\
 	__attribute__((section("__ksymtab_strings"), aligned(1))) \
-	= MODULE_SYMBOL_PREFIX #sym;				\
+	= VMLINUX_SYMBOL_STR(sym);				\
 	static const struct kernel_symbol __ksymtab_##sym	\
 	__used							\
 	__attribute__((section("___ksymtab" sec "+" #sym), unused))	\
@@ -85,5 +97,6 @@ extern struct module __this_module;
 #define EXPORT_UNUSED_SYMBOL_GPL(sym)
 
 #endif /* CONFIG_MODULES */
+#endif /* !__ASSEMBLY__ */
 
 #endif /* _LINUX_EXPORT_H */
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 80d3687..e13e992 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -723,13 +723,6 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
 /* Trap pasters of __FUNCTION__ at compile-time */
 #define __FUNCTION__ (__func__)
 
-/* This helps us to avoid #ifdef CONFIG_SYMBOL_PREFIX */
-#ifdef CONFIG_SYMBOL_PREFIX
-#define SYMBOL_PREFIX CONFIG_SYMBOL_PREFIX
-#else
-#define SYMBOL_PREFIX ""
-#endif
-
 /* Rebuild everything on CONFIG_FTRACE_MCOUNT_RECORD */
 #ifdef CONFIG_FTRACE_MCOUNT_RECORD
 # define REBUILD_DUE_TO_FTRACE_MCOUNT_RECORD
diff --git a/include/linux/module.h b/include/linux/module.h
index ead1b57..46f1ea0 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -190,7 +190,7 @@ extern int modules_disabled; /* for sysctl */
 /* Get/put a kernel symbol (calls must be symmetric) */
 void *__symbol_get(const char *symbol);
 void *__symbol_get_gpl(const char *symbol);
-#define symbol_get(x) ((typeof(&x))(__symbol_get(MODULE_SYMBOL_PREFIX #x)))
+#define symbol_get(x) ((typeof(&x))(__symbol_get(VMLINUX_SYMBOL_STR(x))))
 
 /* modules using other modules: kdb wants to see this. */
 struct module_use {
@@ -453,7 +453,7 @@ extern void __module_put_and_exit(struct module *mod, long code)
 #ifdef CONFIG_MODULE_UNLOAD
 unsigned long module_refcount(struct module *mod);
 void __symbol_put(const char *symbol);
-#define symbol_put(x) __symbol_put(MODULE_SYMBOL_PREFIX #x)
+#define symbol_put(x) __symbol_put(VMLINUX_SYMBOL_STR(x))
 void symbol_put_addr(void *addr);
 
 /* Sometimes we know we already have a refcount, and it's easier not
diff --git a/kernel/modsign_certificate.S b/kernel/modsign_certificate.S
index 246b4c6..4a9a86d 100644
--- a/kernel/modsign_certificate.S
+++ b/kernel/modsign_certificate.S
@@ -1,15 +1,8 @@
-/* SYMBOL_PREFIX defined on commandline from CONFIG_SYMBOL_PREFIX */
-#ifndef SYMBOL_PREFIX
-#define ASM_SYMBOL(sym) sym
-#else
-#define PASTE2(x,y) x##y
-#define PASTE(x,y) PASTE2(x,y)
-#define ASM_SYMBOL(sym) PASTE(SYMBOL_PREFIX, sym)
-#endif
+#include <linux/export.h>
 
 #define GLOBAL(name)	\
-	.globl ASM_SYMBOL(name);	\
-	ASM_SYMBOL(name):
+	.globl VMLINUX_SYMBOL(name);	\
+	VMLINUX_SYMBOL(name):
 
 	.section ".init.data","aw"
 
diff --git a/kernel/module.c b/kernel/module.c
index 0925c9a..cfd4a3f 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1209,7 +1209,7 @@ static inline int check_modstruct_version(Elf_Shdr *sechdrs,
 
 	/* Since this should be found in kernel (which can't be removed),
 	 * no locking is necessary. */
-	if (!find_symbol(MODULE_SYMBOL_PREFIX "module_layout", NULL,
+	if (!find_symbol(VMLINUX_SYMBOL_STR(module_layout), NULL,
 			 &crc, true, false))
 		BUG();
 	return check_version(sechdrs, versindex, "module_layout", mod, crc,
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 07125e6..a373a1f 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -119,13 +119,6 @@ _c_flags += $(if $(patsubst n%,, \
 		$(CFLAGS_GCOV))
 endif
 
-ifdef CONFIG_SYMBOL_PREFIX
-_sym_flags = -DSYMBOL_PREFIX=$(patsubst "%",%,$(CONFIG_SYMBOL_PREFIX))
-_cpp_flags += $(_sym_flags)
-_a_flags += $(_sym_flags)
-endif
-
-
 # If building the kernel in a separate objtree expand all occurrences
 # of -Idir to -I$(srctree)/dir except for absolute paths (starting with '/').
 
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 3d569d6..0149949 100644
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -74,9 +74,8 @@ kallsyms()
 	info KSYM ${2}
 	local kallsymopt;
 
-	if [ -n "${CONFIG_SYMBOL_PREFIX}" ]; then
-		kallsymopt="${kallsymopt} \
-			    --symbol-prefix=${CONFIG_SYMBOL_PREFIX}"
+	if [ -n "${CONFIG_HAVE_UNDERSCORE_SYMBOL_PREFIX}" ]; then
+		kallsymopt="${kallsymopt} --symbol-prefix=_"
 	fi
 
 	if [ -n "${CONFIG_KALLSYMS_ALL}" ]; then
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 78b30c1..6985021 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -18,14 +18,7 @@
 #include "modpost.h"
 #include "../../include/generated/autoconf.h"
 #include "../../include/linux/license.h"
-
-/* Some toolchains use a `_' prefix for all user symbols. */
-#ifdef CONFIG_SYMBOL_PREFIX
-#define MODULE_SYMBOL_PREFIX CONFIG_SYMBOL_PREFIX
-#else
-#define MODULE_SYMBOL_PREFIX ""
-#endif
-
+#include "../../include/linux/export.h"
 
 /* Are we using CONFIG_MODVERSIONS? */
 int modversions = 0;
@@ -562,7 +555,7 @@ static void parse_elf_finish(struct elf_info *info)
 static int ignore_undef_symbol(struct elf_info *info, const char *symname)
 {
 	/* ignore __this_module, it will be resolved shortly */
-	if (strcmp(symname, MODULE_SYMBOL_PREFIX "__this_module") == 0)
+	if (strcmp(symname, VMLINUX_SYMBOL_STR(__this_module)) == 0)
 		return 1;
 	/* ignore global offset table */
 	if (strcmp(symname, "_GLOBAL_OFFSET_TABLE_") == 0)
@@ -583,8 +576,8 @@ static int ignore_undef_symbol(struct elf_info *info, const char *symname)
 	return 0;
 }
 
-#define CRC_PFX     MODULE_SYMBOL_PREFIX "__crc_"
-#define KSYMTAB_PFX MODULE_SYMBOL_PREFIX "__ksymtab_"
+#define CRC_PFX     VMLINUX_SYMBOL_STR(__crc_)
+#define KSYMTAB_PFX VMLINUX_SYMBOL_STR(__ksymtab_)
 
 static void handle_modversions(struct module *mod, struct elf_info *info,
 			       Elf_Sym *sym, const char *symname)
@@ -637,11 +630,11 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
 		}
 #endif
 
-		if (memcmp(symname, MODULE_SYMBOL_PREFIX,
-			   strlen(MODULE_SYMBOL_PREFIX)) == 0) {
+		if (memcmp(symname, VMLINUX_SYMBOL_PREFIX_STR,
+			   strlen(VMLINUX_SYMBOL_PREFIX_STR)) == 0) {
 			mod->unres =
 			  alloc_symbol(symname +
-			               strlen(MODULE_SYMBOL_PREFIX),
+			               strlen(VMLINUX_SYMBOL_PREFIX_STR),
 			               ELF_ST_BIND(sym->st_info) == STB_WEAK,
 			               mod->unres);
 		}
@@ -652,9 +645,9 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
 			sym_add_exported(symname + strlen(KSYMTAB_PFX), mod,
 					export);
 		}
-		if (strcmp(symname, MODULE_SYMBOL_PREFIX "init_module") == 0)
+		if (strcmp(symname, VMLINUX_SYMBOL_STR(init_module)) == 0)
 			mod->has_init = 1;
-		if (strcmp(symname, MODULE_SYMBOL_PREFIX "cleanup_module") == 0)
+		if (strcmp(symname, VMLINUX_SYMBOL_STR(cleanup_module)) == 0)
 			mod->has_cleanup = 1;
 		break;
 	}