[RFC PATCH 13/12] Retpoline vs. CONFIG_TRIM_UNUSED_SYMBOLS

[David Woodhouse]

Arjan pointed out that CONFIG_TRIM_UNUSED_SYMBOLS *really* doesn't like
the dot in the symbols that GCC uses for the thunks.

This seems to work, although my eyes are bleeding just a little bit.

Given this, and the hack we already needed for MODVERSIONS, I wonder if
a better approach might be to export the thunks using underscores in
place of the dots, which is a relatively simple abuse of
__EXPORT_SYMBOL(__x86_indirect_thunk_foo,__x86.indirect_thunk.foo,),
and then have a hack either when generating or loading modules to do
the same replacement.

diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index ccb117a4588b..64d7a45ea954 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -8,7 +8,13 @@
Â#include <asm/export.h>
Â#include <asm/nospec-branch.h>
Â
-.macro THUNK reg
+#ifdef CONFIG_TRIM_UNUSED_KSYMS
+#define EXPORT_REG(reg) __is_defined(__KSYM___x86_indirect_thunk_ ## reg)
+#else
+#define EXPORT_REG(reg)	1
+#endif
+
+.macro THUNK reg export
Â	.section .text.__x86.indirect_thunk.\reg
Â
ÂENTRY(__x86.indirect_thunk.\reg)
@@ -16,15 +22,33 @@ ENTRY(__x86.indirect_thunk.\reg)
Â	NOSPEC_JMP %\reg
Â	CFI_ENDPROC
ÂENDPROC(__x86.indirect_thunk.\reg)
-EXPORT_SYMBOL(__x86.indirect_thunk.\reg)
+
+.if \export
+	EXPORT_SYMBOL_FORCE(__x86.indirect_thunk.\reg)
+.endif
Â.endm
Â
-#ifdef CONFIG_64BIT
-.irp reg rax rbx rcx rdx rsi rdi rbp r8 r9 r10 r11 r12 r13 r14 r15
-	THUNK \reg
-.endr
+#ifdef __KSYM_DEPS__
+#define GENERATE_THUNK(reg) EXPORT_SYMBOL(__x86.indirect_thunk. ## reg)
Â#else
-.irp reg eax ebx ecx edx esi edi ebp
-	THUNK \reg
-.endr
+#define GENERATE_THUNK(reg) THUNK reg EXPORT_REG(reg)
+#endif
+
+GENERATE_THUNK(_ASM_AX)
+GENERATE_THUNK(_ASM_BX)
+GENERATE_THUNK(_ASM_CX)
+GENERATE_THUNK(_ASM_DX)
+GENERATE_THUNK(_ASM_SI)
+GENERATE_THUNK(_ASM_DI)
+GENERATE_THUNK(_ASM_BP)
+GENERATE_THUNK(_ASM_SP)
+#ifdef CONFIG_64BIT
+GENERATE_THUNK(r8)
+GENERATE_THUNK(r9)
+GENERATE_THUNK(r10)
+GENERATE_THUNK(r11)
+GENERATE_THUNK(r12)
+GENERATE_THUNK(r13)
+GENERATE_THUNK(r14)
+GENERATE_THUNK(r15)
Â#endif
diff --git a/include/asm-generic/export.h b/include/asm-generic/export.h
index 719db1968d81..b13bb65e2530 100644
--- a/include/asm-generic/export.h
+++ b/include/asm-generic/export.h
@@ -63,33 +63,33 @@ KSYM(__kcrctab_\name):
Â
Â#if defined(__KSYM_DEPS__)
Â
-#define __EXPORT_SYMBOL(sym, val, sec)	=== __KSYM_##sym ===
+#define __EXPORT_SYMBOL(sym, val, sec, force)	=== __KSYM_##sym ===
Â
Â#elif defined(CONFIG_TRIM_UNUSED_KSYMS)
Â
Â#include <linux/kconfig.h>
Â#include <generated/autoksyms.h>
Â
-#define __EXPORT_SYMBOL(sym, val, sec)				\
-	__cond_export_sym(sym, val, sec, __is_defined(__KSYM_##sym))
+#define __EXPORT_SYMBOL(sym, val, sec, force)			\
+	Â__cond_export_sym(sym, val, sec, __or(force, __is_defined(__KSYM_##sym)))
Â#define __cond_export_sym(sym, val, sec, conf)			\
Â	___cond_export_sym(sym, val, sec, conf)
Â#define ___cond_export_sym(sym, val, sec, enabled)		\
Â	__cond_export_sym_##enabled(sym, val, sec)
Â#define __cond_export_sym_1(sym, val, sec) ___EXPORT_SYMBOL sym, val, sec
Â#define __cond_export_sym_0(sym, val, sec) /* nothing */
-
Â#else
-#define __EXPORT_SYMBOL(sym, val, sec) ___EXPORT_SYMBOL sym, val, sec
+#define __EXPORT_SYMBOL(sym, val, sec, force)	___EXPORT_SYMBOL sym, val, sec
Â#endif
Â
Â#define EXPORT_SYMBOL(name)					\
-	__EXPORT_SYMBOL(name, KSYM_FUNC(KSYM(name)),)
+	__EXPORT_SYMBOL(name, KSYM_FUNC(KSYM(name)), , 0)
Â#define EXPORT_SYMBOL_GPL(name)Â				\
-	__EXPORT_SYMBOL(name, KSYM_FUNC(KSYM(name)), _gpl)
+	__EXPORT_SYMBOL(name, KSYM_FUNC(KSYM(name)), _gpl, 0)
Â#define EXPORT_DATA_SYMBOL(name)				\
-	__EXPORT_SYMBOL(name, KSYM(name),)
+	__EXPORT_SYMBOL(name, KSYM(name), , 0)
Â#define EXPORT_DATA_SYMBOL_GPL(name)				\
-	__EXPORT_SYMBOL(name, KSYM(name),_gpl)
-
+	__EXPORT_SYMBOL(name, KSYM(name), _gpl, 0)
+#define EXPORT_SYMBOL_FORCE(name)				\
+	__EXPORT_SYMBOL(name, KSYM(name), , 1)
Â#endif
diff --git a/scripts/adjust_autoksyms.sh b/scripts/adjust_autoksyms.sh
index 513da1a4a2da..991cd136291b 100755
--- a/scripts/adjust_autoksyms.sh
+++ b/scripts/adjust_autoksyms.sh
@@ -60,7 +60,7 @@ cat > "$new_ksyms_file" << EOT
Â
ÂEOT
Â[ "$(ls -A "$MODVERDIR")" ] &&
-sed -ns -e '3{s/ /\n/g;/^$/!p;}' "$MODVERDIR"/*.mod | sort -u |
+sed -ns -e '3{s/ /\n/g;/^$/!p;}' "$MODVERDIR"/*.mod | sort -u | tr . _ |
Âwhile read sym; do
Â	if [ -n "$CONFIG_HAVE_UNDERSCORE_SYMBOL_PREFIX" ]; then
Â		sym="${sym#_}"

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