Re: [PATCH 2/3] riscv: Workaround mcount name prior to clang-13

On Thu, Mar 25, 2021 at 3:38 PM Nathan Chancellor nathan@kernel.org wrote:

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.

Cc: stable@vger.kernel.org Link: https://github.com/ClangBuiltLinux/linux/issues/1331 Signed-off-by: Nathan Chancellor nathan@kernel.org

Thanks for keeping this alive on clang-10, and resolving it for future releases! Reviewed-by: Nick Desaulniers ndesaulniers@google.com

---

arch/riscv/include/asm/ftrace.h | 14 ++++++++++++-- arch/riscv/kernel/mcount.S | 10 +++++----- scripts/recordmcount.pl | 2 +- 3 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h index 845002cc2e57..04dad3380041 100644 --- 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 8a5593ff9ff3..6d462681c9c0 100644 --- 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 a36df04cfa09..7b83a1aaec98 100755 --- a/scripts/recordmcount.pl +++ b/scripts/recordmcount.pl @@ -392,7 +392,7 @@ 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") {

2.31.0

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