refactor rela section scanning

Upon realizing that there is no point in correlating rela entries,
I also realized that tracking the status of rela entries is also
not needed.

Additionally, the rela section correlation path (really misnamed
as it is the rela section _comparison path) is VERY hot.  Particularly
on files like fs/ext4/ext4.o (which create-diff-object currently can't
successfully parse entirely):

Samples: 40K of event 'cycles', Event count (approx.): 36516578362
49.49%  create-diff-obj  create-diff-object  [.] rela_equal
31.85%  create-diff-obj  create-diff-object  [.] kpatch_correlate_relas
16.22%  create-diff-obj  create-diff-object  [.] find_symbol_by_index

The refactor does a few things:
- replaces nested for loops with single for loop when comparing rela entries
- removes status field for rela entires
- compares rela and nonrela sections in the same path
- removes unnecessary setting of status fields as the inclusion tree
  will include them even if the section status isn't set to CHANGED. This is
  even better as unchanged sections won't appear as CHANGED just because
  their partner .text or .rela section is CHANGED.

This drastically reduced runtime for larger objects and cooled the rela
comparison path:

87.64%  create-diff-obj  create-diff-object  [.] find_symbol_by_index
6.98%  create-diff-obj  libc-2.18.so        [.] __GI___strcmp_ssse3
1.33%  create-diff-obj  create-diff-object  [.] find_section_by_index
1.16%  create-diff-obj  create-diff-object  [.] kpatch_correlate_symbols
0.61%  create-diff-obj  create-diff-object  [.] kpatch_create_rela_table
0.52%  create-diff-obj  create-diff-object  [.] kpatch_correlate_sections

Signed-off-by: Seth Jennings <sjenning@redhat.com>

kpatch-build/create-diff-object.c

@@ -126,7 +126,6 @@ struct rela {
 	int addend;
 	int offset;
 	char *string;
-	enum status status;
 };
 
 #define for_each_entry(iter, entry, table, type) \
@@ -445,10 +444,57 @@ struct kpatch_elf *kpatch_elf_open(const char *name)
 	return kelf;
 }
 
+int rela_equal(struct rela *rela1, struct rela *rela2)
+{
+	if (rela1->type != rela2->type ||
+	    rela1->offset != rela2->offset)
+		return 0;
+
+	if (rela1->string) {
+		if (rela2->string &&
+		    !strcmp(rela1->string, rela2->string))
+			return 1;
+	} else {
+		if (strcmp(rela1->sym->name, rela2->sym->name))
+			return 0;
+		if (rela1->addend == rela2->addend)
+			return 1;
+	}
+
+	return 0;
+}
+
+void kpatch_compare_correlated_rela_section(struct section *sec)
+{
+	struct rela *rela1, *rela2;
+	int i;
+
+	for_each_rela(i, rela1, &sec->relas) {
+		rela2 = &((struct rela *)(sec->twin->relas.data))[i];
+		if (rela_equal(rela1, rela2))
+			continue;
+		sec->status = CHANGED;
+		return;
+	}
+
+	sec->status = SAME;
+}
+
 void kpatch_compare_correlated_nonrela_section(struct section *sec)
 {
 	struct section *sec1 = sec, *sec2 = sec->twin;
 
+	if (sec1->sh.sh_type != SHT_NOBITS &&
+	    memcmp(sec1->data->d_buf, sec2->data->d_buf, sec1->data->d_size))
+		sec->status = CHANGED;
+	else
+		sec->status = SAME;
+}
+
+void kpatch_compare_correlated_section(struct section *sec)
+{
+	struct section *sec1 = sec, *sec2 = sec->twin;
+
 	/* Compare section headers (must match or fatal) */
 	if (sec1->sh.sh_type != sec2->sh.sh_type ||
 	    sec1->sh.sh_flags != sec2->sh.sh_flags ||
@@ -459,34 +505,36 @@ void kpatch_compare_correlated_nonrela_section(struct section *sec)
 		DIFF_FATAL("%s section header details differ", sec1->name);
 
 	if (sec1->sh.sh_size != sec2->sh.sh_size ||
-	    sec1->data->d_size != sec2->data->d_size || 
+	    sec1->data->d_size != sec2->data->d_size) {
-	    (sec1->sh.sh_type != SHT_NOBITS &&
+		sec->status = CHANGED;
-	     memcmp(sec1->data->d_buf, sec2->data->d_buf, sec1->data->d_size)))
+		return;
-		sec1->status = CHANGED;
+	}
+
+	if (is_rela_section(sec))
+		kpatch_compare_correlated_rela_section(sec);
 	else
-		sec1->status = SAME;
+		kpatch_compare_correlated_nonrela_section(sec);
 }
 
-void kpatch_compare_correlated_nonrela_sections(struct table *table)
+void kpatch_compare_sections(struct table *table)
 {
 	struct section *sec;
 	int i;
 
 	for_each_section(i, sec, table) {
-		if (is_rela_section(sec))
-			continue;
 		if (sec->twin)
-			kpatch_compare_correlated_nonrela_section(sec);
+			kpatch_compare_correlated_section(sec);
 		else
 			sec->status = NEW;
 
-		/* sync any rela section and associated symbols */
+		/* sync symbol status */
-		if (sec->sym)
+		if (is_rela_section(sec)) {
-			sec->sym->status = sec->status;
+			if (sec->base->sym && sec->base->sym->status != CHANGED)
-		if (sec->secsym)
+				sec->base->sym->status = sec->status;
-			sec->secsym->status = sec->status;
+		} else {
-		if (sec->rela)
+			if (sec->sym && sec->sym->status != CHANGED)
-			sec->rela->status = sec->status;
+				sec->sym->status = sec->status;
+		}
 	}
 }
 
@@ -508,9 +556,14 @@ void kpatch_compare_correlated_symbol(struct symbol *sym)
 	if (sym1->sym.st_shndx == SHN_UNDEF ||
 	     sym1->sym.st_shndx == SHN_ABS)
 		sym1->status = SAME;
+
+	/*
+	 * The status of LOCAL symbols is dependent on the status of their
+	 * matching section and is set during section comparison.
+	 */
 }
 
-void kpatch_compare_correlated_symbols(struct table *table)
+void kpatch_compare_symbols(struct table *table)
 {
 	struct symbol *sym;
 	int i;
@@ -532,7 +585,6 @@ void kpatch_correlate_sections(struct table *table1, struct table *table2)
 	struct section *sec1, *sec2;
 	int i, j;
 
-	/* correlate all sections and compare nonrela sections */
 	for_each_section(i, sec1, table1) {
 		for_each_section(j, sec2, table2) {
 			if (strcmp(sec1->name, sec2->name))
@@ -568,41 +620,6 @@ void kpatch_correlate_symbols(struct table *table1, struct table *table2)
 	}
 }
 
-int rela_equal(struct rela *rela1, struct rela *rela2)
-{
-	if (rela1->type != rela2->type ||
-	    rela1->offset != rela2->offset)
-		return 0;
-
-	if (rela1->string) {
-		if (rela2->string &&
-		    !strcmp(rela1->string, rela2->string))
-			return 1;
-	} else {
-		if (strcmp(rela1->sym->name, rela2->sym->name))
-			return 0;
-		if (rela1->addend == rela2->addend)
-			return 1;
-	}
-
-	return 0;
-}
-
-void kpatch_correlate_relas(struct section *sec)
-{
-	struct rela *rela1, *rela2;
-	int i, j;
-
-	for_each_rela(i, rela1, &sec->relas) {
-		for_each_rela(j, rela2, &sec->twin->relas) {
-			    if (rela_equal(rela1, rela2)) {
-				rela1->status = rela2->status = SAME;
-				break;
-			}
-		}
-	}
-}
-
 void kpatch_compare_elf_headers(Elf *elf1, Elf *elf2)
 {
 	GElf_Ehdr eh1, eh2;
@@ -637,60 +654,17 @@ void kpatch_check_program_headers(Elf *elf)
 		DIFF_FATAL("ELF contains program header");
 }
 
-void kpatch_set_rela_section_status(struct section *sec)
-{
-	struct rela *rela;
-	int i;
-
-	for_each_rela(i, rela, &sec->relas)
-		if (rela->status == NEW) {
-			/*
-			 * This rela section is different. Make
-			 * sure the text section and any associated
-			 * symbols come along too.
-			 */
-			sec->status = CHANGED;
-			sec->base->status = CHANGED;
-			if (sec->base->sym)
-				sec->base->sym->status = CHANGED;
-			if (sec->base->secsym)
-				sec->base->secsym->status = CHANGED;
-			return;
-		}
-
-	/*
-	 * The difference in the section data was due to the renumeration
-	 * of symbol indexes.  Consider this rela section unchanged.
-	 */
-	sec->status = SAME;
-}
-
 void kpatch_correlate_elfs(struct kpatch_elf *kelf1, struct kpatch_elf *kelf2)
 {
-	struct section *sec;
-	int i;
-
 	kpatch_correlate_sections(&kelf1->sections, &kelf2->sections);
 	kpatch_correlate_symbols(&kelf1->symbols, &kelf2->symbols);
-
-	/* at this point, sections are correlated, we can use sec->twin */
-	for_each_section(i, sec, &kelf1->sections)
-		if (is_rela_section(sec))
-			kpatch_correlate_relas(sec);
 }
 
 void kpatch_compare_correlated_elements(struct kpatch_elf *kelf)
 {
-	struct section *sec;
-	int i;
-
 	/* tables are already correlated at this point */
-	kpatch_compare_correlated_nonrela_sections(&kelf->sections);
+	kpatch_compare_sections(&kelf->sections);
-	kpatch_compare_correlated_symbols(&kelf->symbols);
+	kpatch_compare_symbols(&kelf->symbols);
-
-	for_each_section(i, sec, &kelf->sections)
-		if (is_rela_section(sec) && sec->status == SAME)
-			kpatch_set_rela_section_status(sec);
 }
 
 void kpatch_replace_sections_syms(struct kpatch_elf *kelf)
@@ -733,13 +707,12 @@ void kpatch_dump_kelf(struct kpatch_elf *kelf)
 			printf(", base-> %s\n", sec->base->name);
 			printf("rela section expansion\n");
 			for_each_rela(j, rela, &sec->relas) {
-				printf("sym %lu, offset %d, type %d, %s %s %d %s\n",
+				printf("sym %lu, offset %d, type %d, %s %s %d\n",
 				       GELF_R_SYM(rela->rela.r_info),
 				       rela->offset, rela->type,
 				       rela->sym->name,
 				       (rela->addend < 0)?"-":"+",
-				       abs(rela->addend),
+				       abs(rela->addend));
-				       status_str(rela->status));
 			}
 		} else {
 			if (sec->sym)