Re: [RFC PATCH 3/3] objtool/mcount: Add powerpc specific functions

Peter Zijlstra wrote:

On Fri, Mar 18, 2022 at 04:21:40PM +0530, Sathvika Vasireddy wrote:

quoted

This patch adds powerpc specific functions required for
'objtool mcount' to work, and enables mcount for ppc.

I would love to see more objtool enablement for Power :-)

quoted

diff --git a/tools/objtool/arch/powerpc/include/arch/elf.h b/tools/objtool/arch/powerpc/include/arch/elf.h
new file mode 100644
index 000000000000..3c8ebb7d2a6b
--- /dev/null
+++ b/tools/objtool/arch/powerpc/include/arch/elf.h

@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef _OBJTOOL_ARCH_ELF
+#define _OBJTOOL_ARCH_ELF
+
+#define R_NONE R_PPC_NONE
+
+#endif /* _OBJTOOL_ARCH_ELF */

diff --git a/tools/objtool/utils.c b/tools/objtool/utils.c
index d1fc6a123a6e..c9c14fa0dfd7 100644
--- a/tools/objtool/utils.c
+++ b/tools/objtool/utils.c

@@ -179,11 +179,29 @@ int create_mcount_loc_sections(struct objtool_file *file)
 		loc = (unsigned long *)sec->data->d_buf + idx;
 		memset(loc, 0, sizeof(unsigned long));
 
-		if (elf_add_reloc_to_insn(file->elf, sec,
-					  idx * sizeof(unsigned long),
-					  R_X86_64_64,
-					  insn->sec, insn->offset))
-			return -1;
+		if (file->elf->ehdr.e_machine == EM_X86_64) {
+			if (elf_add_reloc_to_insn(file->elf, sec,
+						  idx * sizeof(unsigned long),
+						  R_X86_64_64,
+						  insn->sec, insn->offset))
+				return -1;
+		}
+
+		if (file->elf->ehdr.e_machine == EM_PPC64) {
+			if (elf_add_reloc_to_insn(file->elf, sec,
+						  idx * sizeof(unsigned long),
+						  R_PPC64_ADDR64,
+						  insn->sec, insn->offset))
+				return -1;
+		}
+
+		if (file->elf->ehdr.e_machine == EM_PPC) {
+			if (elf_add_reloc_to_insn(file->elf, sec,
+						  idx * sizeof(unsigned long),
+						  R_PPC_ADDR32,
+						  insn->sec, insn->offset))
+				return -1;
+		}

It appears to me that repeating this code 3 times doesn't really scale
well, how about we introduce a helper like:


int elf_reloc_type_long(struct elf *elf)
{
	switch (elf->ehdr.e_machine) {
	case EM_X86_64:
		return R_X86_64_64;
	case EM_PPC64:
		return R_PPC64_ADDR64;
	case EM_PPC:
		return R_PPC_ADDR32;
	default:
		WARN("unknown machine...")
		exit(-1);
	}
}

		if (elf_add_reloc_to_insn(file->elf, sec,
					  idx * sizeof(unsigned long),
					  elf_reloc_type_long(file->elf),
					  insn->sec, insn->offset))
			return -1;

Good point. I suppose we'll need a similar helper, say, 
elf_reloc_type_none(), to replace R_NONE usage if we want to have 
objtool work for cross-arch builds.


- Naveen