From b958ed601c3fe2bbdd09c089deb3fbbc13a48f59 Mon Sep 17 00:00:00 2001
From: Josh Poimboeuf <jpoimboe@redhat.com>
Date: Mon, 11 May 2020 23:05:54 -0400
Subject: [PATCH] create-diff-object: Add ppc64le mcount support

Add the __mcount_loc section on ppc64le.  It has pointers to all the
mcount calls.  This will enable the ftrace hook to be used for patched
functions.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com> (rebased)
---
 kpatch-build/create-diff-object.c | 89 ++++++++++++++++++++-----------
 test/unit/objs                    |  2 +-
 2 files changed, 59 insertions(+), 32 deletions(-)

diff --git a/kpatch-build/create-diff-object.c b/kpatch-build/create-diff-object.c
index b14b613..f17f500 100644
--- a/kpatch-build/create-diff-object.c
+++ b/kpatch-build/create-diff-object.c
@@ -3322,9 +3322,6 @@ static void kpatch_create_callbacks_objname_rela(struct kpatch_elf *kelf, char *
 	}
 }
 
-#ifdef __powerpc64__
-void kpatch_create_mcount_sections(struct kpatch_elf *kelf) { }
-#else
 /*
  * This function basically reimplements the functionality of the Linux
  * recordmcount script, so that patched functions can be recognized by ftrace.
@@ -3337,9 +3334,9 @@ static void kpatch_create_mcount_sections(struct kpatch_elf *kelf)
 	int nr, index;
 	struct section *sec, *relasec;
 	struct symbol *sym;
-	struct rela *rela;
-	void *newdata;
-	unsigned char *insn;
+	struct rela *rela, *mcount_rela;
+	void **funcs;
+	unsigned long insn_offset;
 
 	nr = 0;
 	list_for_each_entry(sym, &kelf->symbols, list)
@@ -3363,36 +3360,40 @@ static void kpatch_create_mcount_sections(struct kpatch_elf *kelf)
 			continue;
 		}
 
-		/* add rela in .rela__mcount_loc to fill in function pointer */
-		ALLOC_LINK(rela, &relasec->relas);
-		rela->sym = sym;
-		rela->type = R_X86_64_64;
-		rela->addend = 0;
-		rela->offset = (unsigned int)(index * sizeof(void*));
+#ifdef __x86_64__
+
+		rela = list_first_entry(&sym->sec->rela->relas, struct rela, list);
 
 		/*
-		 * Modify the first instruction of the function to "callq
-		 * __fentry__" so that ftrace will be happy.
+		 * For "call fentry", the relocation points to 1 byte past the
+		 * beginning of the instruction.
 		 */
-		newdata = malloc(sym->sec->data->d_size);
-		if (!newdata)
-			ERROR("malloc");
+		insn_offset = rela->offset - 1;
 
-		memcpy(newdata, sym->sec->data->d_buf, sym->sec->data->d_size);
-		sym->sec->data->d_buf = newdata;
-		insn = newdata;
-
-		rela = list_first_entry(&sym->sec->rela->relas, struct rela,
-					list);
-
-		/*
-		 * R_X86_64_NONE is only generated by older versions of kernel/gcc
-		 * which use the mcount script.
-		 */
 		if (rela->type == R_X86_64_NONE) {
+			void *newdata;
+			unsigned char *insn;
+
+			/*
+			 * R_X86_64_NONE is only generated by older versions of
+			 * kernel/gcc which use the mcount script.  There's a
+			 * NOP instead of a call to fentry.
+			 */
+
+			/* Make a writable copy of the text section data */
+			newdata = malloc(sym->sec->data->d_size);
+			memcpy(newdata, sym->sec->data->d_buf, sym->sec->data->d_size);
+			sym->sec->data->d_buf = newdata;
+			insn = newdata;
+
+			/*
+			 * Replace the NOP with a call to fentry.  The fentry
+			 * rela symbol is already there, just need to change
+			 * the relocation type accordingly.
+			 */
+			insn = sym->sec->data->d_buf;
 			if (insn[0] != 0xf)
-				ERROR("%s: unexpected instruction at the start of the function",
-				      sym->name);
+				ERROR("%s: unexpected instruction at the start of the function", sym->name);
 			insn[0] = 0xe8;
 			insn[1] = 0;
 			insn[2] = 0;
@@ -3402,6 +3403,33 @@ static void kpatch_create_mcount_sections(struct kpatch_elf *kelf)
 			rela->type = R_X86_64_PC32;
 		}
 
+#else /* __powerpc64__ */
+{
+		bool found = false;
+
+		list_for_each_entry(rela, &sym->sec->rela->relas, list)
+			if (!strcmp(rela->sym->name, "_mcount")) {
+				found = true;
+				break;
+			}
+
+		if (!found)
+			ERROR("%s: unexpected missing call to _mcount()", __func__);
+
+		insn_offset = rela->offset;
+}
+#endif
+		/*
+		 * 'rela' points to the mcount/fentry call.
+		 *
+		 * Create a .rela__mcount_loc entry which also points to it.
+		 */
+		ALLOC_LINK(mcount_rela, &relasec->relas);
+		mcount_rela->sym = sym;
+		mcount_rela->type = ABSOLUTE_RELA_TYPE;
+		mcount_rela->addend = insn_offset - sym->sym.st_value;
+		mcount_rela->offset = (unsigned int) (index * sizeof(*funcs));
+
 		index++;
 	}
 
@@ -3409,7 +3437,6 @@ static void kpatch_create_mcount_sections(struct kpatch_elf *kelf)
 	if (index != nr)
 		ERROR("size mismatch in funcs sections");
 }
-#endif
 
 /*
  * This function strips out symbols that were referenced by changed rela
diff --git a/test/unit/objs b/test/unit/objs
index 42df5fb..59b5841 160000
--- a/test/unit/objs
+++ b/test/unit/objs
@@ -1 +1 @@
-Subproject commit 42df5fbc85632c4bab836e104210fe5fd52ae1e5
+Subproject commit 59b5841598dc2d01e750a2b21547ffa243a09894