git/hash.h
Ævar Arnfjörð Bjarmason 9dc523aa0e Makefile + hash.h: remove PPC_SHA1 implementation
Remove the PPC_SHA1 implementation added in a6ef3518f9 ([PATCH] PPC
assembly implementation of SHA1, 2005-04-22). When this was added
Apple consumer hardware used the PPC architecture, and the
implementation was intended to improve SHA-1 speed there.

Since it was added we've moved to using sha1collisiondetection by
default, and anyone wanting hard-rolled non-DC SHA-1 implementation
can use OpenSSL's via the OPENSSL_SHA1 knob.

The PPC_SHA1 originally originally targeted 32 bit PPC, and later the
64 bit PPC 970 (a.k.a. Apple PowerPC G5). See 926172c5e4 (block-sha1:
improve code on large-register-set machines, 2009-08-10) for a
reference about the performance on G5 (a comment in block-sha1/sha1.c
being removed here).

I can't get it to do anything but segfault on both the BE and LE POWER
machines in the GCC compile farm[1]. Anyone who's concerned about
performance on PPC these days is likely to be using the IBM POWER
processors.

There have been proposals to entirely remove non-sha1collisiondetection
implementations from the tree[2]. I think per [3] that would be a bit
overzealous. I.e. there are various set-ups git's speed is going to be
more important than the relatively implausible SHA-1 collision attack,
or where such attacks are entirely mitigated by other means (e.g. by
incoming objects being checked with DC_SHA1).

But that really doesn't apply to PPC_SHA1 in particular, which seems
to have outlived its usefulness.

As this gets rid of the only in-tree *.S assembly file we can remove
the small bits of logic from the Makefile needed to build objects
from *.S (as opposed to *.c)

The code being removed here was also throwing warnings with the
"-pedantic" flag, it could have been fixed as 544d93bc3b (block-sha1:
remove use of obsolete x86 assembly, 2022-03-10) did for block-sha1/*,
but as noted above let's remove it instead.

1. https://cfarm.tetaneutral.net/machines/list/
   Tested on gcc{110,112,135,203}, a mixture of POWER [789] ppc64 and
   ppc64le. All segfault in anything needing object
   hashing (e.g. t/t1007-hash-object.sh) when compiled with
   PPC_SHA1=Y.
2. https://lore.kernel.org/git/20200223223758.120941-1-mh@glandium.org/
3. https://lore.kernel.org/git/20200224044732.GK1018190@coredump.intra.peff.net/

Acked-by: brian m. carlson" <sandals@crustytoothpaste.net>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2022-08-31 14:37:31 -07:00

341 lines
9.3 KiB
C

#ifndef HASH_H
#define HASH_H
#include "git-compat-util.h"
#include "repository.h"
#if defined(SHA1_APPLE)
#include <CommonCrypto/CommonDigest.h>
#elif defined(SHA1_OPENSSL)
#include <openssl/sha.h>
#elif defined(SHA1_DC)
#include "sha1dc_git.h"
#else /* SHA1_BLK */
#include "block-sha1/sha1.h"
#endif
#if defined(SHA256_NETTLE)
#include "sha256/nettle.h"
#elif defined(SHA256_GCRYPT)
#define SHA256_NEEDS_CLONE_HELPER
#include "sha256/gcrypt.h"
#elif defined(SHA256_OPENSSL)
#include <openssl/sha.h>
#else
#include "sha256/block/sha256.h"
#endif
#ifndef platform_SHA_CTX
/*
* platform's underlying implementation of SHA-1; could be OpenSSL,
* blk_SHA, Apple CommonCrypto, etc... Note that the relevant
* SHA-1 header may have already defined platform_SHA_CTX for our
* own implementations like block-sha1, so we list
* the default for OpenSSL compatible SHA-1 implementations here.
*/
#define platform_SHA_CTX SHA_CTX
#define platform_SHA1_Init SHA1_Init
#define platform_SHA1_Update SHA1_Update
#define platform_SHA1_Final SHA1_Final
#endif
#define git_SHA_CTX platform_SHA_CTX
#define git_SHA1_Init platform_SHA1_Init
#define git_SHA1_Update platform_SHA1_Update
#define git_SHA1_Final platform_SHA1_Final
#ifndef platform_SHA256_CTX
#define platform_SHA256_CTX SHA256_CTX
#define platform_SHA256_Init SHA256_Init
#define platform_SHA256_Update SHA256_Update
#define platform_SHA256_Final SHA256_Final
#endif
#define git_SHA256_CTX platform_SHA256_CTX
#define git_SHA256_Init platform_SHA256_Init
#define git_SHA256_Update platform_SHA256_Update
#define git_SHA256_Final platform_SHA256_Final
#ifdef platform_SHA256_Clone
#define git_SHA256_Clone platform_SHA256_Clone
#endif
#ifdef SHA1_MAX_BLOCK_SIZE
#include "compat/sha1-chunked.h"
#undef git_SHA1_Update
#define git_SHA1_Update git_SHA1_Update_Chunked
#endif
static inline void git_SHA1_Clone(git_SHA_CTX *dst, const git_SHA_CTX *src)
{
memcpy(dst, src, sizeof(*dst));
}
#ifndef SHA256_NEEDS_CLONE_HELPER
static inline void git_SHA256_Clone(git_SHA256_CTX *dst, const git_SHA256_CTX *src)
{
memcpy(dst, src, sizeof(*dst));
}
#endif
/*
* Note that these constants are suitable for indexing the hash_algos array and
* comparing against each other, but are otherwise arbitrary, so they should not
* be exposed to the user or serialized to disk. To know whether a
* git_hash_algo struct points to some usable hash function, test the format_id
* field for being non-zero. Use the name field for user-visible situations and
* the format_id field for fixed-length fields on disk.
*/
/* An unknown hash function. */
#define GIT_HASH_UNKNOWN 0
/* SHA-1 */
#define GIT_HASH_SHA1 1
/* SHA-256 */
#define GIT_HASH_SHA256 2
/* Number of algorithms supported (including unknown). */
#define GIT_HASH_NALGOS (GIT_HASH_SHA256 + 1)
/* "sha1", big-endian */
#define GIT_SHA1_FORMAT_ID 0x73686131
/* The length in bytes and in hex digits of an object name (SHA-1 value). */
#define GIT_SHA1_RAWSZ 20
#define GIT_SHA1_HEXSZ (2 * GIT_SHA1_RAWSZ)
/* The block size of SHA-1. */
#define GIT_SHA1_BLKSZ 64
/* "s256", big-endian */
#define GIT_SHA256_FORMAT_ID 0x73323536
/* The length in bytes and in hex digits of an object name (SHA-256 value). */
#define GIT_SHA256_RAWSZ 32
#define GIT_SHA256_HEXSZ (2 * GIT_SHA256_RAWSZ)
/* The block size of SHA-256. */
#define GIT_SHA256_BLKSZ 64
/* The length in byte and in hex digits of the largest possible hash value. */
#define GIT_MAX_RAWSZ GIT_SHA256_RAWSZ
#define GIT_MAX_HEXSZ GIT_SHA256_HEXSZ
/* The largest possible block size for any supported hash. */
#define GIT_MAX_BLKSZ GIT_SHA256_BLKSZ
struct object_id {
unsigned char hash[GIT_MAX_RAWSZ];
int algo; /* XXX requires 4-byte alignment */
};
/* A suitably aligned type for stack allocations of hash contexts. */
union git_hash_ctx {
git_SHA_CTX sha1;
git_SHA256_CTX sha256;
};
typedef union git_hash_ctx git_hash_ctx;
typedef void (*git_hash_init_fn)(git_hash_ctx *ctx);
typedef void (*git_hash_clone_fn)(git_hash_ctx *dst, const git_hash_ctx *src);
typedef void (*git_hash_update_fn)(git_hash_ctx *ctx, const void *in, size_t len);
typedef void (*git_hash_final_fn)(unsigned char *hash, git_hash_ctx *ctx);
typedef void (*git_hash_final_oid_fn)(struct object_id *oid, git_hash_ctx *ctx);
struct git_hash_algo {
/*
* The name of the algorithm, as appears in the config file and in
* messages.
*/
const char *name;
/* A four-byte version identifier, used in pack indices. */
uint32_t format_id;
/* The length of the hash in binary. */
size_t rawsz;
/* The length of the hash in hex characters. */
size_t hexsz;
/* The block size of the hash. */
size_t blksz;
/* The hash initialization function. */
git_hash_init_fn init_fn;
/* The hash context cloning function. */
git_hash_clone_fn clone_fn;
/* The hash update function. */
git_hash_update_fn update_fn;
/* The hash finalization function. */
git_hash_final_fn final_fn;
/* The hash finalization function for object IDs. */
git_hash_final_oid_fn final_oid_fn;
/* The OID of the empty tree. */
const struct object_id *empty_tree;
/* The OID of the empty blob. */
const struct object_id *empty_blob;
/* The all-zeros OID. */
const struct object_id *null_oid;
};
extern const struct git_hash_algo hash_algos[GIT_HASH_NALGOS];
/*
* Return a GIT_HASH_* constant based on the name. Returns GIT_HASH_UNKNOWN if
* the name doesn't match a known algorithm.
*/
int hash_algo_by_name(const char *name);
/* Identical, except based on the format ID. */
int hash_algo_by_id(uint32_t format_id);
/* Identical, except based on the length. */
int hash_algo_by_length(int len);
/* Identical, except for a pointer to struct git_hash_algo. */
static inline int hash_algo_by_ptr(const struct git_hash_algo *p)
{
return p - hash_algos;
}
#define the_hash_algo the_repository->hash_algo
const struct object_id *null_oid(void);
static inline int hashcmp_algop(const unsigned char *sha1, const unsigned char *sha2, const struct git_hash_algo *algop)
{
/*
* Teach the compiler that there are only two possibilities of hash size
* here, so that it can optimize for this case as much as possible.
*/
if (algop->rawsz == GIT_MAX_RAWSZ)
return memcmp(sha1, sha2, GIT_MAX_RAWSZ);
return memcmp(sha1, sha2, GIT_SHA1_RAWSZ);
}
static inline int hashcmp(const unsigned char *sha1, const unsigned char *sha2)
{
return hashcmp_algop(sha1, sha2, the_hash_algo);
}
static inline int oidcmp(const struct object_id *oid1, const struct object_id *oid2)
{
const struct git_hash_algo *algop;
if (!oid1->algo)
algop = the_hash_algo;
else
algop = &hash_algos[oid1->algo];
return hashcmp_algop(oid1->hash, oid2->hash, algop);
}
static inline int hasheq_algop(const unsigned char *sha1, const unsigned char *sha2, const struct git_hash_algo *algop)
{
/*
* We write this here instead of deferring to hashcmp so that the
* compiler can properly inline it and avoid calling memcmp.
*/
if (algop->rawsz == GIT_MAX_RAWSZ)
return !memcmp(sha1, sha2, GIT_MAX_RAWSZ);
return !memcmp(sha1, sha2, GIT_SHA1_RAWSZ);
}
static inline int hasheq(const unsigned char *sha1, const unsigned char *sha2)
{
return hasheq_algop(sha1, sha2, the_hash_algo);
}
static inline int oideq(const struct object_id *oid1, const struct object_id *oid2)
{
const struct git_hash_algo *algop;
if (!oid1->algo)
algop = the_hash_algo;
else
algop = &hash_algos[oid1->algo];
return hasheq_algop(oid1->hash, oid2->hash, algop);
}
static inline int is_null_oid(const struct object_id *oid)
{
return oideq(oid, null_oid());
}
static inline void hashcpy(unsigned char *sha_dst, const unsigned char *sha_src)
{
memcpy(sha_dst, sha_src, the_hash_algo->rawsz);
}
static inline void oidcpy(struct object_id *dst, const struct object_id *src)
{
memcpy(dst->hash, src->hash, GIT_MAX_RAWSZ);
dst->algo = src->algo;
}
/* Like oidcpy() but zero-pads the unused bytes in dst's hash array. */
static inline void oidcpy_with_padding(struct object_id *dst,
const struct object_id *src)
{
size_t hashsz;
if (!src->algo)
hashsz = the_hash_algo->rawsz;
else
hashsz = hash_algos[src->algo].rawsz;
memcpy(dst->hash, src->hash, hashsz);
memset(dst->hash + hashsz, 0, GIT_MAX_RAWSZ - hashsz);
dst->algo = src->algo;
}
static inline struct object_id *oiddup(const struct object_id *src)
{
struct object_id *dst = xmalloc(sizeof(struct object_id));
oidcpy(dst, src);
return dst;
}
static inline void hashclr(unsigned char *hash)
{
memset(hash, 0, the_hash_algo->rawsz);
}
static inline void oidclr(struct object_id *oid)
{
memset(oid->hash, 0, GIT_MAX_RAWSZ);
oid->algo = hash_algo_by_ptr(the_hash_algo);
}
static inline void oidread(struct object_id *oid, const unsigned char *hash)
{
memcpy(oid->hash, hash, the_hash_algo->rawsz);
oid->algo = hash_algo_by_ptr(the_hash_algo);
}
static inline int is_empty_blob_sha1(const unsigned char *sha1)
{
return hasheq(sha1, the_hash_algo->empty_blob->hash);
}
static inline int is_empty_blob_oid(const struct object_id *oid)
{
return oideq(oid, the_hash_algo->empty_blob);
}
static inline int is_empty_tree_sha1(const unsigned char *sha1)
{
return hasheq(sha1, the_hash_algo->empty_tree->hash);
}
static inline int is_empty_tree_oid(const struct object_id *oid)
{
return oideq(oid, the_hash_algo->empty_tree);
}
static inline void oid_set_algo(struct object_id *oid, const struct git_hash_algo *algop)
{
oid->algo = hash_algo_by_ptr(algop);
}
const char *empty_tree_oid_hex(void);
const char *empty_blob_oid_hex(void);
#endif