riscv: Workaround mcount name prior to clang-13

[ Upstream commit 7ce04771503074a7de7f539cc43f5e1b385cb99b ]

Prior to clang 13.0.0, the RISC-V name for the mcount symbol was
"mcount", which differs from the GCC version of "_mcount", which results
in the following errors:

riscv64-linux-gnu-ld: init/main.o: in function `__traceiter_initcall_level':
main.c:(.text+0xe): undefined reference to `mcount'
riscv64-linux-gnu-ld: init/main.o: in function `__traceiter_initcall_start':
main.c:(.text+0x4e): undefined reference to `mcount'
riscv64-linux-gnu-ld: init/main.o: in function `__traceiter_initcall_finish':
main.c:(.text+0x92): undefined reference to `mcount'
riscv64-linux-gnu-ld: init/main.o: in function `.LBB32_28':
main.c:(.text+0x30c): undefined reference to `mcount'
riscv64-linux-gnu-ld: init/main.o: in function `free_initmem':
main.c:(.text+0x54c): undefined reference to `mcount'

This has been corrected in https://reviews.llvm.org/D98881 but the
minimum supported clang version is 10.0.1. To avoid build errors and to
gain a working function tracer, adjust the name of the mcount symbol for
older versions of clang in mount.S and recordmcount.pl.

Link: https://github.com/ClangBuiltLinux/linux/issues/1331
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
index 845002c..04dad33 100644 (file)
--- a/arch/riscv/include/asm/ftrace.h
+++ b/arch/riscv/include/asm/ftrace.h
@@ -13,9 +13,19 @@
 #endif
 #define HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
 
+/*
+ * Clang prior to 13 had "mcount" instead of "_mcount":
+ * https://reviews.llvm.org/D98881
+ */
+#if defined(CONFIG_CC_IS_GCC) || CONFIG_CLANG_VERSION >= 130000
+#define MCOUNT_NAME _mcount
+#else
+#define MCOUNT_NAME mcount
+#endif
+
 #define ARCH_SUPPORTS_FTRACE_OPS 1
 #ifndef __ASSEMBLY__
-void _mcount(void);
+void MCOUNT_NAME(void);
 static inline unsigned long ftrace_call_adjust(unsigned long addr)
 {
        return addr;
@@ -36,7 +46,7 @@ struct dyn_arch_ftrace {
  * both auipc and jalr at the same time.
  */
 
-#define MCOUNT_ADDR            ((unsigned long)_mcount)
+#define MCOUNT_ADDR            ((unsigned long)MCOUNT_NAME)
 #define JALR_SIGN_MASK         (0x00000800)
 #define JALR_OFFSET_MASK       (0x00000fff)
 #define AUIPC_OFFSET_MASK      (0xfffff000)

diff --git a/arch/riscv/kernel/mcount.S b/arch/riscv/kernel/mcount.S
index 8a5593f..6d46268 100644 (file)
--- a/arch/riscv/kernel/mcount.S
+++ b/arch/riscv/kernel/mcount.S
@@ -47,8 +47,8 @@
 
 ENTRY(ftrace_stub)
 #ifdef CONFIG_DYNAMIC_FTRACE
-       .global _mcount
-       .set    _mcount, ftrace_stub
+       .global MCOUNT_NAME
+       .set    MCOUNT_NAME, ftrace_stub
 #endif
        ret
 ENDPROC(ftrace_stub)
@@ -78,7 +78,7 @@ ENDPROC(return_to_handler)
 #endif
 
 #ifndef CONFIG_DYNAMIC_FTRACE
-ENTRY(_mcount)
+ENTRY(MCOUNT_NAME)
        la      t4, ftrace_stub
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
        la      t0, ftrace_graph_return
@@ -124,6 +124,6 @@ do_trace:
        jalr    t5
        RESTORE_ABI_STATE
        ret
-ENDPROC(_mcount)
+ENDPROC(MCOUNT_NAME)
 #endif
-EXPORT_SYMBOL(_mcount)
+EXPORT_SYMBOL(MCOUNT_NAME)

diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl
index 857d5b7..4f84657 100755 (executable)
--- a/scripts/recordmcount.pl
+++ b/scripts/recordmcount.pl
@@ -395,7 +395,7 @@ if ($arch eq "x86_64") {
     $mcount_regex = "^\\s*([0-9a-fA-F]+):.*\\s_mcount\$";
 } elsif ($arch eq "riscv") {
     $function_regex = "^([0-9a-fA-F]+)\\s+<([^.0-9][0-9a-zA-Z_\\.]+)>:";
-    $mcount_regex = "^\\s*([0-9a-fA-F]+):\\sR_RISCV_CALL(_PLT)?\\s_mcount\$";
+    $mcount_regex = "^\\s*([0-9a-fA-F]+):\\sR_RISCV_CALL(_PLT)?\\s_?mcount\$";
     $type = ".quad";
     $alignment = 2;
 } elsif ($arch eq "nds32") {