linux-kernel - [RFC PATCH 2/6] modpost: deduplicate section

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Date:   Thu, 21 Jul 2022 23:24:12 -0300
From:   Mauricio Faria de Oliveira <mfo@...onical.com>
To:     linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org,
        linux-kbuild@...r.kernel.org, linux-fsdevel@...r.kernel.org
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>
Subject: [RFC PATCH 2/6] modpost: deduplicate section_rel[a]()

Now both functions are almost identical, and we can again generalize
the relocation types Elf_Rela/Elf_Rel with Elf_Rela, and handle some
differences with conditionals on section header type (SHT_RELA/REL).

The important bit is to make sure the loop increment uses the right
size for pointer arithmethic.

The original reason for split functions to make program logic easier
to follow; commit 5b24c0715fc4 ("kbuild: code refactoring in modpost").

Hopefully these 2 commits may help improving that, without an impact
in understanding the code due to generalization of relocation types.

Signed-off-by: Mauricio Faria de Oliveira <mfo@...onical.com>
---
 scripts/mod/modpost.c | 61 ++++++++++++++++---------------------------
 1 file changed, 23 insertions(+), 38 deletions(-)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 4c1038dccae0..d1ed67fa290b 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1794,63 +1794,49 @@ static int get_relx_sym(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *rela,
 	return 0;
 }
 
-static void section_rela(const char *modname, struct elf_info *elf,
+/* The caller must ensure sechdr->sh_type == SHT_RELA or SHT_REL. */
+static void section_relx(const char *modname, struct elf_info *elf,
 			 Elf_Shdr *sechdr)
 {
 	Elf_Sym  *sym;
-	Elf_Rela *rela;
+	Elf_Rela *relx; /* access .r_addend in SHT_RELA _only_! */
 	Elf_Rela r;
+	size_t relx_size;
 	const char *fromsec;
 
 	Elf_Rela *start = (void *)elf->hdr + sechdr->sh_offset;
 	Elf_Rela *stop  = (void *)start + sechdr->sh_size;
 
 	fromsec = sech_name(elf, sechdr);
-	fromsec += strlen(".rela");
+	if (sechdr->sh_type == SHT_RELA) {
+		relx_size = sizeof(Elf_Rela);
+		fromsec += strlen(".rela");
+	} else if (sechdr->sh_type == SHT_REL) {
+		relx_size = sizeof(Elf_Rel);
+		fromsec += strlen(".rel");
+	} else {
+		error("%s: [%s.ko] not relocation section\n", fromsec, modname);
+		return;
+	}
+
 	/* if from section (name) is know good then skip it */
 	if (match(fromsec, section_white_list))
 		return;
 
-	for (rela = start; rela < stop; rela++) {
-		if (get_relx_sym(elf, sechdr, rela, &r, &sym))
+	for (relx = start; relx < stop; relx = (void *)relx + relx_size) {
+		if (get_relx_sym(elf, sechdr, relx, &r, &sym))
 			continue;
 
 		switch (elf->hdr->e_machine) {
 		case EM_RISCV:
-			if (!strcmp("__ex_table", fromsec) &&
+			if (sechdr->sh_type == SHT_RELA &&
+			    !strcmp("__ex_table", fromsec) &&
 			    ELF_R_TYPE(r.r_info) == R_RISCV_SUB32)
 				continue;
 			break;
 		}
 
-		if (is_second_extable_reloc(start, rela, fromsec))
-			find_extable_entry_size(fromsec, &r);
-		check_section_mismatch(modname, elf, &r, sym, fromsec);
-	}
-}
-
-static void section_rel(const char *modname, struct elf_info *elf,
-			Elf_Shdr *sechdr)
-{
-	Elf_Sym *sym;
-	Elf_Rel *rel;
-	Elf_Rela r;
-	const char *fromsec;
-
-	Elf_Rel *start = (void *)elf->hdr + sechdr->sh_offset;
-	Elf_Rel *stop  = (void *)start + sechdr->sh_size;
-
-	fromsec = sech_name(elf, sechdr);
-	fromsec += strlen(".rel");
-	/* if from section (name) is know good then skip it */
-	if (match(fromsec, section_white_list))
-		return;
-
-	for (rel = start; rel < stop; rel++) {
-		if (get_relx_sym(elf, sechdr, (Elf_Rela *)rel, &r, &sym)
-			continue;
-
-		if (is_second_extable_reloc(start, rel, fromsec))
+		if (is_second_extable_reloc(start, relx, fromsec))
 			find_extable_entry_size(fromsec, &r);
 		check_section_mismatch(modname, elf, &r, sym, fromsec);
 	}
@@ -1877,10 +1863,9 @@ static void check_sec_ref(const char *modname, struct elf_info *elf)
 	for (i = 0; i < elf->num_sections; i++) {
 		check_section(modname, elf, &elf->sechdrs[i]);
 		/* We want to process only relocation sections and not .init */
-		if (sechdrs[i].sh_type == SHT_RELA)
-			section_rela(modname, elf, &elf->sechdrs[i]);
-		else if (sechdrs[i].sh_type == SHT_REL)
-			section_rel(modname, elf, &elf->sechdrs[i]);
+		if (sechdrs[i].sh_type == SHT_RELA ||
+		    sechdrs[i].sh_type == SHT_REL)
+			section_relx(modname, elf, &elf->sechdrs[i]);
 	}
 }
 
-- 
2.25.1