linux-kernel - [PATCH] x86, relocs: add manual debug mode

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Message-ID: <20140121203223.GA12649@www.outflux.net>
Date:	Tue, 21 Jan 2014 12:32:23 -0800
From:	Kees Cook <keescook@...omium.org>
To:	linux-kernel@...r.kernel.org
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Kees Cook <keescook@...omium.org>,
	Michael Davidson <md@...gle.com>, Cong Ding <dinggnu@...il.com>
Subject: [PATCH] x86, relocs: add manual debug mode

From: Michael Davidson <md@...gle.com>

Improve the debuggability of relocations output. When trying to compare
the output between different linkers, it's handy to be able to see the
section names in output.

Signed-off-by: Michael Davidson <md@...gle.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/x86/tools/relocs.c        |   30 +++++++++++++++++++++++++++++-
 arch/x86/tools/relocs.h        |    7 ++++---
 arch/x86/tools/relocs_common.c |   16 ++++++++++++----
 3 files changed, 45 insertions(+), 8 deletions(-)

diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
index 11f9285a2ff6..cfbdbdb4e173 100644
--- a/arch/x86/tools/relocs.c
+++ b/arch/x86/tools/relocs.c
@@ -1025,6 +1025,29 @@ static void emit_relocs(int as_text, int use_real_mode)
 	}
 }
 
+/*
+ * As an aid to debugging problems with different linkers
+ * print summary information about the relocs.
+ * Since different linkers tend to emit the sections in
+ * different orders we use the section names in the output.
+ */
+static int do_reloc_info(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
+				const char *symname)
+{
+	printf("%s\t%s\t%s\t%s\n",
+		sec_name(sec->shdr.sh_info),
+		rel_type(ELF_R_TYPE(rel->r_info)),
+		symname,
+		sec_name(sym->st_shndx));
+	return 0;
+}
+
+static void print_reloc_info(void)
+{
+	printf("reloc section\treloc type\tsymbol\tsymbol section\n");
+	walk_relocs(do_reloc_info);
+}
+
 #if ELF_BITS == 64
 # define process process_64
 #else
@@ -1032,7 +1055,8 @@ static void emit_relocs(int as_text, int use_real_mode)
 #endif
 
 void process(FILE *fp, int use_real_mode, int as_text,
-	     int show_absolute_syms, int show_absolute_relocs)
+	     int show_absolute_syms, int show_absolute_relocs,
+	     int show_reloc_info)
 {
 	regex_init(use_real_mode);
 	read_ehdr(fp);
@@ -1050,5 +1074,9 @@ void process(FILE *fp, int use_real_mode, int as_text,
 		print_absolute_relocs();
 		return;
 	}
+	if (show_reloc_info) {
+		print_reloc_info();
+		return;
+	}
 	emit_relocs(as_text, use_real_mode);
 }
diff --git a/arch/x86/tools/relocs.h b/arch/x86/tools/relocs.h
index 07cdb1eca4fa..f59590645b68 100644
--- a/arch/x86/tools/relocs.h
+++ b/arch/x86/tools/relocs.h
@@ -29,8 +29,9 @@ enum symtype {
 };
 
 void process_32(FILE *fp, int use_real_mode, int as_text,
-		int show_absolute_syms, int show_absolute_relocs);
+		int show_absolute_syms, int show_absolute_relocs,
+		int show_reloc_info);
 void process_64(FILE *fp, int use_real_mode, int as_text,
-		int show_absolute_syms, int show_absolute_relocs);
-
+		int show_absolute_syms, int show_absolute_relocs,
+		int show_reloc_info);
 #endif /* RELOCS_H */
diff --git a/arch/x86/tools/relocs_common.c b/arch/x86/tools/relocs_common.c
index 44d396823a53..acab636bcb34 100644
--- a/arch/x86/tools/relocs_common.c
+++ b/arch/x86/tools/relocs_common.c
@@ -11,12 +11,13 @@ void die(char *fmt, ...)
 
 static void usage(void)
 {
-	die("relocs [--abs-syms|--abs-relocs|--text|--realmode] vmlinux\n");
+	die("relocs [--abs-syms|--abs-relocs|--reloc-info|--text|--realmode]" \
+	    " vmlinux\n");
 }
 
 int main(int argc, char **argv)
 {
-	int show_absolute_syms, show_absolute_relocs;
+	int show_absolute_syms, show_absolute_relocs, show_reloc_info;
 	int as_text, use_real_mode;
 	const char *fname;
 	FILE *fp;
@@ -25,6 +26,7 @@ int main(int argc, char **argv)
 
 	show_absolute_syms = 0;
 	show_absolute_relocs = 0;
+	show_reloc_info = 0;
 	as_text = 0;
 	use_real_mode = 0;
 	fname = NULL;
@@ -39,6 +41,10 @@ int main(int argc, char **argv)
 				show_absolute_relocs = 1;
 				continue;
 			}
+			if (strcmp(arg, "--reloc-info") == 0) {
+				show_reloc_info = 1;
+				continue;
+			}
 			if (strcmp(arg, "--text") == 0) {
 				as_text = 1;
 				continue;
@@ -67,10 +73,12 @@ int main(int argc, char **argv)
 	rewind(fp);
 	if (e_ident[EI_CLASS] == ELFCLASS64)
 		process_64(fp, use_real_mode, as_text,
-			   show_absolute_syms, show_absolute_relocs);
+			   show_absolute_syms, show_absolute_relocs,
+			   show_reloc_info);
 	else
 		process_32(fp, use_real_mode, as_text,
-			   show_absolute_syms, show_absolute_relocs);
+			   show_absolute_syms, show_absolute_relocs,
+			   show_reloc_info);
 	fclose(fp);
 	return 0;
 }
-- 
1.7.9.5


-- 
Kees Cook
Chrome OS Security
--
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