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