[RFC PATCH v1] objtool: Use target file endianness instead of a compiled constant

[RFC PATCH v1] objtool: Use target file endianness instead of a compiled constant

[Christophe Leroy]

Some architectures like powerpc support both endianness, it's
therefore not possible to fix the endianness via arch/endianness.h
because there is no easy way to get the target endianness at
build time.

Use the endianness recorded in the file objtool is working on.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 .../arch/x86/include/arch/endianness.h        |  9 ------
 tools/objtool/check.c                         |  2 +-
 tools/objtool/include/objtool/endianness.h    | 29 +++++++++----------
 tools/objtool/orc_dump.c                      |  4 +--
 tools/objtool/orc_gen.c                       |  4 +--
 tools/objtool/special.c                       |  3 +-
 6 files changed, 20 insertions(+), 31 deletions(-)
 delete mode 100644 tools/objtool/arch/x86/include/arch/endianness.h

diff --git a/tools/objtool/arch/x86/include/arch/endianness.h b/tools/objtool/arch/x86/include/arch/endianness.h
deleted file mode 100644
index 7c362527da20..000000000000
--- a/tools/objtool/arch/x86/include/arch/endianness.h
+++ /dev/null
@@ -1,9 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-or-later */
-#ifndef _ARCH_ENDIANNESS_H
-#define _ARCH_ENDIANNESS_H
-
-#include <endian.h>
-
-#define __TARGET_BYTE_ORDER __LITTLE_ENDIAN
-
-#endif /* _ARCH_ENDIANNESS_H */
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 6de5085e3e5a..378d4e2de285 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1941,7 +1941,7 @@ static int read_unwind_hints(struct objtool_file *file)
 			return -1;
 		}
 
-		cfi.cfa.offset = bswap_if_needed(hint->sp_offset);
+		cfi.cfa.offset = bswap_if_needed(&file->elf->ehdr, hint->sp_offset);
 		cfi.type = hint->type;
 		cfi.end = hint->end;
 
diff --git a/tools/objtool/include/objtool/endianness.h b/tools/objtool/include/objtool/endianness.h
index 10241341eff3..2c7469a7645b 100644
--- a/tools/objtool/include/objtool/endianness.h
+++ b/tools/objtool/include/objtool/endianness.h
@@ -2,33 +2,30 @@
 #ifndef _OBJTOOL_ENDIANNESS_H
 #define _OBJTOOL_ENDIANNESS_H
 
-#include <arch/endianness.h>
 #include <linux/kernel.h>
 #include <endian.h>
-
-#ifndef __TARGET_BYTE_ORDER
-#error undefined arch __TARGET_BYTE_ORDER
-#endif
-
-#if __BYTE_ORDER != __TARGET_BYTE_ORDER
-#define __NEED_BSWAP 1
-#else
-#define __NEED_BSWAP 0
-#endif
+#include <objtool/elf.h>
 
 /*
- * Does a byte swap if target endianness doesn't match the host, i.e. cross
+ * Does a byte swap if target file endianness doesn't match the host, i.e. cross
  * compilation for little endian on big endian and vice versa.
  * To be used for multi-byte values conversion, which are read from / about
  * to be written to a target native endianness ELF file.
  */
-#define bswap_if_needed(val)						\
+static inline bool need_bswap(GElf_Ehdr *ehdr)
+{
+	return (__BYTE_ORDER == __LITTLE_ENDIAN) ^
+	       (ehdr->e_ident[EI_DATA] == ELFDATA2LSB);
+}
+
+#define bswap_if_needed(ehdr, val)					\
 ({									\
 	__typeof__(val) __ret;						\
+	bool __need_bswap = need_bswap(ehdr);				\
 	switch (sizeof(val)) {						\
-	case 8: __ret = __NEED_BSWAP ? bswap_64(val) : (val); break;	\
-	case 4: __ret = __NEED_BSWAP ? bswap_32(val) : (val); break;	\
-	case 2: __ret = __NEED_BSWAP ? bswap_16(val) : (val); break;	\
+	case 8: __ret = __need_bswap ? bswap_64(val) : (val); break;	\
+	case 4: __ret = __need_bswap ? bswap_32(val) : (val); break;	\
+	case 2: __ret = __need_bswap ? bswap_16(val) : (val); break;	\
 	default:							\
 		BUILD_BUG(); break;					\
 	}								\
diff --git a/tools/objtool/orc_dump.c b/tools/objtool/orc_dump.c
index f5a8508c42d6..5a51586c6ad2 100644
--- a/tools/objtool/orc_dump.c
+++ b/tools/objtool/orc_dump.c
@@ -198,11 +198,11 @@ int orc_dump(const char *_objname)
 
 		printf(" sp:");
 
-		print_reg(orc[i].sp_reg, bswap_if_needed(orc[i].sp_offset));
+		print_reg(orc[i].sp_reg, bswap_if_needed(elf64_getehdr(elf), orc[i].sp_offset));
 
 		printf(" bp:");
 
-		print_reg(orc[i].bp_reg, bswap_if_needed(orc[i].bp_offset));
+		print_reg(orc[i].bp_reg, bswap_if_needed(elf64_getehdr(elf), orc[i].bp_offset));
 
 		printf(" type:%s end:%d\n",
 		       orc_type_name(orc[i].type), orc[i].end);
diff --git a/tools/objtool/orc_gen.c b/tools/objtool/orc_gen.c
index dd3c64af9db2..63c36ed284a5 100644
--- a/tools/objtool/orc_gen.c
+++ b/tools/objtool/orc_gen.c
@@ -97,8 +97,8 @@ static int write_orc_entry(struct elf *elf, struct section *orc_sec,
 	/* populate ORC data */
 	orc = (struct orc_entry *)orc_sec->data->d_buf + idx;
 	memcpy(orc, o, sizeof(*orc));
-	orc->sp_offset = bswap_if_needed(orc->sp_offset);
-	orc->bp_offset = bswap_if_needed(orc->bp_offset);
+	orc->sp_offset = bswap_if_needed(&elf->ehdr, orc->sp_offset);
+	orc->bp_offset = bswap_if_needed(&elf->ehdr, orc->bp_offset);
 
 	/* populate reloc for ip */
 	if (elf_add_reloc_to_insn(elf, ip_sec, idx * sizeof(int), R_X86_64_PC32,
diff --git a/tools/objtool/special.c b/tools/objtool/special.c
index e2223dd91c37..ae563c524416 100644
--- a/tools/objtool/special.c
+++ b/tools/objtool/special.c
@@ -87,7 +87,8 @@ static int get_alt_entry(struct elf *elf, struct special_entry *entry,
 	if (entry->feature) {
 		unsigned short feature;
 
-		feature = bswap_if_needed(*(unsigned short *)(sec->data->d_buf +
+		feature = bswap_if_needed(&elf->ehdr,
+					  *(unsigned short *)(sec->data->d_buf +
 							      offset +
 							      entry->feature));
 		arch_handle_alternative(feature, alt);
-- 
2.35.1

Re: [RFC PATCH v1] objtool: Use target file endianness instead of a compiled constant

[Peter Zijlstra]

On Thu, Mar 31, 2022 at 09:52:07AM +0200, Christophe Leroy wrote:
> Some architectures like powerpc support both endianness, it's
> therefore not possible to fix the endianness via arch/endianness.h
> because there is no easy way to get the target endianness at
> build time.
> 
> Use the endianness recorded in the file objtool is working on.
> 

> +#include <objtool/elf.h>
>  
>  /*
> - * Does a byte swap if target endianness doesn't match the host, i.e. cross
> + * Does a byte swap if target file endianness doesn't match the host, i.e. cross
>   * compilation for little endian on big endian and vice versa.
>   * To be used for multi-byte values conversion, which are read from / about
>   * to be written to a target native endianness ELF file.
>   */
> -#define bswap_if_needed(val)						\
> +static inline bool need_bswap(GElf_Ehdr *ehdr)
> +{
> +	return (__BYTE_ORDER == __LITTLE_ENDIAN) ^
> +	       (ehdr->e_ident[EI_DATA] == ELFDATA2LSB);
> +}
> +
> +#define bswap_if_needed(ehdr, val)					\
>  ({									\
>  	__typeof__(val) __ret;						\
> +	bool __need_bswap = need_bswap(ehdr);				\
>  	switch (sizeof(val)) {						\
> -	case 8: __ret = __NEED_BSWAP ? bswap_64(val) : (val); break;	\
> -	case 4: __ret = __NEED_BSWAP ? bswap_32(val) : (val); break;	\
> -	case 2: __ret = __NEED_BSWAP ? bswap_16(val) : (val); break;	\
> +	case 8: __ret = __need_bswap ? bswap_64(val) : (val); break;	\
> +	case 4: __ret = __need_bswap ? bswap_32(val) : (val); break;	\
> +	case 2: __ret = __need_bswap ? bswap_16(val) : (val); break;	\
>  	default:							\
>  		BUILD_BUG(); break;					\
>  	}								\

Far less painfull that I imagined it would be,.. but I think I prefer
passing in elf, as opposed to elf->ehdr, would that work?

Re: [RFC PATCH v1] objtool: Use target file endianness instead of a compiled constant

[Christophe Leroy]

Le 31/03/2022 à 10:08, Peter Zijlstra a écrit :
> On Thu, Mar 31, 2022 at 09:52:07AM +0200, Christophe Leroy wrote:
>> Some architectures like powerpc support both endianness, it's
>> therefore not possible to fix the endianness via arch/endianness.h
>> because there is no easy way to get the target endianness at
>> build time.
>>
>> Use the endianness recorded in the file objtool is working on.
>>
> 
>> +#include <objtool/elf.h>
>>   
>>   /*
>> - * Does a byte swap if target endianness doesn't match the host, i.e. cross
>> + * Does a byte swap if target file endianness doesn't match the host, i.e. cross
>>    * compilation for little endian on big endian and vice versa.
>>    * To be used for multi-byte values conversion, which are read from / about
>>    * to be written to a target native endianness ELF file.
>>    */
>> -#define bswap_if_needed(val)						\
>> +static inline bool need_bswap(GElf_Ehdr *ehdr)
>> +{
>> +	return (__BYTE_ORDER == __LITTLE_ENDIAN) ^
>> +	       (ehdr->e_ident[EI_DATA] == ELFDATA2LSB);
>> +}
>> +
>> +#define bswap_if_needed(ehdr, val)					\
>>   ({									\
>>   	__typeof__(val) __ret;						\
>> +	bool __need_bswap = need_bswap(ehdr);				\
>>   	switch (sizeof(val)) {						\
>> -	case 8: __ret = __NEED_BSWAP ? bswap_64(val) : (val); break;	\
>> -	case 4: __ret = __NEED_BSWAP ? bswap_32(val) : (val); break;	\
>> -	case 2: __ret = __NEED_BSWAP ? bswap_16(val) : (val); break;	\
>> +	case 8: __ret = __need_bswap ? bswap_64(val) : (val); break;	\
>> +	case 4: __ret = __need_bswap ? bswap_32(val) : (val); break;	\
>> +	case 2: __ret = __need_bswap ? bswap_16(val) : (val); break;	\
>>   	default:							\
>>   		BUILD_BUG(); break;					\
>>   	}								\
> 
> Far less painfull that I imagined it would be,.. but I think I prefer
> passing in elf, as opposed to elf->ehdr, would that work?

That's what I wanted to do in the beginning, but we don't have it in 
orc_dump()

Christophe