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>
This commit is contained in:
Ævar Arnfjörð Bjarmason 2022-08-31 11:18:43 +02:00 committed by Junio C Hamano
parent d42b38dfb5
commit 9dc523aa0e
8 changed files with 8 additions and 347 deletions

View file

@ -135,8 +135,7 @@ Issues of note:
By default, git uses OpenSSL for SHA1 but it will use its own
library (inspired by Mozilla's) with either NO_OPENSSL or
BLK_SHA1. Also included is a version optimized for PowerPC
(PPC_SHA1).
BLK_SHA1.
- "libcurl" library is used for fetching and pushing
repositories over http:// or https://, as well as by

View file

@ -155,9 +155,6 @@ include shared.mak
# Define BLK_SHA1 environment variable to make use of the bundled
# optimized C SHA1 routine.
#
# Define PPC_SHA1 environment variable when running make to make use of
# a bundled SHA1 routine optimized for PowerPC.
#
# Define DC_SHA1 to unconditionally enable the collision-detecting sha1
# algorithm. This is slower, but may detect attempted collision attacks.
# Takes priority over other *_SHA1 knobs.
@ -1802,6 +1799,10 @@ ifdef APPLE_COMMON_CRYPTO
SHA1_MAX_BLOCK_SIZE = 1024L*1024L*1024L
endif
ifdef PPC_SHA1
$(error the PPC_SHA1 flag has been removed along with the PowerPC-specific SHA-1 implementation.)
endif
ifdef OPENSSL_SHA1
EXTLIBS += $(LIB_4_CRYPTO)
BASIC_CFLAGS += -DSHA1_OPENSSL
@ -1810,10 +1811,6 @@ ifdef BLK_SHA1
LIB_OBJS += block-sha1/sha1.o
BASIC_CFLAGS += -DSHA1_BLK
else
ifdef PPC_SHA1
LIB_OBJS += ppc/sha1.o ppc/sha1ppc.o
BASIC_CFLAGS += -DSHA1_PPC
else
ifdef APPLE_COMMON_CRYPTO
COMPAT_CFLAGS += -DCOMMON_DIGEST_FOR_OPENSSL
BASIC_CFLAGS += -DSHA1_APPLE
@ -1847,7 +1844,6 @@ endif
endif
endif
endif
endif
ifdef OPENSSL_SHA256
EXTLIBS += $(LIB_4_CRYPTO)
@ -2594,14 +2590,10 @@ missing_compdb_dir =
compdb_args =
endif
ASM_SRC := $(wildcard $(OBJECTS:o=S))
ASM_OBJ := $(ASM_SRC:S=o)
C_OBJ := $(filter-out $(ASM_OBJ),$(OBJECTS))
C_OBJ := $(OBJECTS)
$(C_OBJ): %.o: %.c GIT-CFLAGS $(missing_dep_dirs) $(missing_compdb_dir)
$(QUIET_CC)$(CC) -o $*.o -c $(dep_args) $(compdb_args) $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) $<
$(ASM_OBJ): %.o: %.S GIT-CFLAGS $(missing_dep_dirs) $(missing_compdb_dir)
$(QUIET_CC)$(CC) -o $*.o -c $(dep_args) $(compdb_args) $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) $<
%.s: %.c GIT-CFLAGS FORCE
$(QUIET_CC)$(CC) -o $@ -S $(ALL_CFLAGS) $(EXTRA_CPPFLAGS) $<

View file

@ -28,10 +28,6 @@
* try to do the silly "optimize away loads" part because it won't
* see what the value will be).
*
* Ben Herrenschmidt reports that on PPC, the C version comes close
* to the optimized asm with this (ie on PPC you don't want that
* 'volatile', since there are lots of registers).
*
* On ARM we get the best code generation by forcing a full memory barrier
* between each SHA_ROUND, otherwise gcc happily get wild with spilling and
* the stack frame size simply explode and performance goes down the drain.

View file

@ -237,9 +237,6 @@ AC_MSG_NOTICE([CHECKS for site configuration])
# tests. These tests take up a significant amount of the total test time
# but are not needed unless you plan to talk to SVN repos.
#
# Define PPC_SHA1 environment variable when running make to make use of
# a bundled SHA1 routine optimized for PowerPC.
#
# Define NO_OPENSSL environment variable if you do not have OpenSSL.
#
# Define OPENSSLDIR=/foo/bar if your openssl header and library files are in

6
hash.h
View file

@ -4,9 +4,7 @@
#include "git-compat-util.h"
#include "repository.h"
#if defined(SHA1_PPC)
#include "ppc/sha1.h"
#elif defined(SHA1_APPLE)
#if defined(SHA1_APPLE)
#include <CommonCrypto/CommonDigest.h>
#elif defined(SHA1_OPENSSL)
#include <openssl/sha.h>
@ -32,7 +30,7 @@
* 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 and ppc-sha1, so we list
* own implementations like block-sha1, so we list
* the default for OpenSSL compatible SHA-1 implementations here.
*/
#define platform_SHA_CTX SHA_CTX

View file

@ -1,72 +0,0 @@
/*
* SHA-1 implementation.
*
* Copyright (C) 2005 Paul Mackerras <paulus@samba.org>
*
* This version assumes we are running on a big-endian machine.
* It calls an external sha1_core() to process blocks of 64 bytes.
*/
#include <stdio.h>
#include <string.h>
#include "sha1.h"
void ppc_sha1_core(uint32_t *hash, const unsigned char *p,
unsigned int nblocks);
int ppc_SHA1_Init(ppc_SHA_CTX *c)
{
c->hash[0] = 0x67452301;
c->hash[1] = 0xEFCDAB89;
c->hash[2] = 0x98BADCFE;
c->hash[3] = 0x10325476;
c->hash[4] = 0xC3D2E1F0;
c->len = 0;
c->cnt = 0;
return 0;
}
int ppc_SHA1_Update(ppc_SHA_CTX *c, const void *ptr, unsigned long n)
{
unsigned long nb;
const unsigned char *p = ptr;
c->len += (uint64_t) n << 3;
while (n != 0) {
if (c->cnt || n < 64) {
nb = 64 - c->cnt;
if (nb > n)
nb = n;
memcpy(&c->buf.b[c->cnt], p, nb);
if ((c->cnt += nb) == 64) {
ppc_sha1_core(c->hash, c->buf.b, 1);
c->cnt = 0;
}
} else {
nb = n >> 6;
ppc_sha1_core(c->hash, p, nb);
nb <<= 6;
}
n -= nb;
p += nb;
}
return 0;
}
int ppc_SHA1_Final(unsigned char *hash, ppc_SHA_CTX *c)
{
unsigned int cnt = c->cnt;
c->buf.b[cnt++] = 0x80;
if (cnt > 56) {
if (cnt < 64)
memset(&c->buf.b[cnt], 0, 64 - cnt);
ppc_sha1_core(c->hash, c->buf.b, 1);
cnt = 0;
}
if (cnt < 56)
memset(&c->buf.b[cnt], 0, 56 - cnt);
c->buf.l[7] = c->len;
ppc_sha1_core(c->hash, c->buf.b, 1);
memcpy(hash, c->hash, 20);
return 0;
}

View file

@ -1,25 +0,0 @@
/*
* SHA-1 implementation.
*
* Copyright (C) 2005 Paul Mackerras <paulus@samba.org>
*/
#include <stdint.h>
typedef struct {
uint32_t hash[5];
uint32_t cnt;
uint64_t len;
union {
unsigned char b[64];
uint64_t l[8];
} buf;
} ppc_SHA_CTX;
int ppc_SHA1_Init(ppc_SHA_CTX *c);
int ppc_SHA1_Update(ppc_SHA_CTX *c, const void *p, unsigned long n);
int ppc_SHA1_Final(unsigned char *hash, ppc_SHA_CTX *c);
#define platform_SHA_CTX ppc_SHA_CTX
#define platform_SHA1_Init ppc_SHA1_Init
#define platform_SHA1_Update ppc_SHA1_Update
#define platform_SHA1_Final ppc_SHA1_Final

View file

@ -1,224 +0,0 @@
/*
* SHA-1 implementation for PowerPC.
*
* Copyright (C) 2005 Paul Mackerras <paulus@samba.org>
*/
/*
* PowerPC calling convention:
* %r0 - volatile temp
* %r1 - stack pointer.
* %r2 - reserved
* %r3-%r12 - Incoming arguments & return values; volatile.
* %r13-%r31 - Callee-save registers
* %lr - Return address, volatile
* %ctr - volatile
*
* Register usage in this routine:
* %r0 - temp
* %r3 - argument (pointer to 5 words of SHA state)
* %r4 - argument (pointer to data to hash)
* %r5 - Constant K in SHA round (initially number of blocks to hash)
* %r6-%r10 - Working copies of SHA variables A..E (actually E..A order)
* %r11-%r26 - Data being hashed W[].
* %r27-%r31 - Previous copies of A..E, for final add back.
* %ctr - loop count
*/
/*
* We roll the registers for A, B, C, D, E around on each
* iteration; E on iteration t is D on iteration t+1, and so on.
* We use registers 6 - 10 for this. (Registers 27 - 31 hold
* the previous values.)
*/
#define RA(t) (((t)+4)%5+6)
#define RB(t) (((t)+3)%5+6)
#define RC(t) (((t)+2)%5+6)
#define RD(t) (((t)+1)%5+6)
#define RE(t) (((t)+0)%5+6)
/* We use registers 11 - 26 for the W values */
#define W(t) ((t)%16+11)
/* Register 5 is used for the constant k */
/*
* The basic SHA-1 round function is:
* E += ROTL(A,5) + F(B,C,D) + W[i] + K; B = ROTL(B,30)
* Then the variables are renamed: (A,B,C,D,E) = (E,A,B,C,D).
*
* Every 20 rounds, the function F() and the constant K changes:
* - 20 rounds of f0(b,c,d) = "bit wise b ? c : d" = (^b & d) + (b & c)
* - 20 rounds of f1(b,c,d) = b^c^d = (b^d)^c
* - 20 rounds of f2(b,c,d) = majority(b,c,d) = (b&d) + ((b^d)&c)
* - 20 more rounds of f1(b,c,d)
*
* These are all scheduled for near-optimal performance on a G4.
* The G4 is a 3-issue out-of-order machine with 3 ALUs, but it can only
* *consider* starting the oldest 3 instructions per cycle. So to get
* maximum performance out of it, you have to treat it as an in-order
* machine. Which means interleaving the computation round t with the
* computation of W[t+4].
*
* The first 16 rounds use W values loaded directly from memory, while the
* remaining 64 use values computed from those first 16. We preload
* 4 values before starting, so there are three kinds of rounds:
* - The first 12 (all f0) also load the W values from memory.
* - The next 64 compute W(i+4) in parallel. 8*f0, 20*f1, 20*f2, 16*f1.
* - The last 4 (all f1) do not do anything with W.
*
* Therefore, we have 6 different round functions:
* STEPD0_LOAD(t,s) - Perform round t and load W(s). s < 16
* STEPD0_UPDATE(t,s) - Perform round t and compute W(s). s >= 16.
* STEPD1_UPDATE(t,s)
* STEPD2_UPDATE(t,s)
* STEPD1(t) - Perform round t with no load or update.
*
* The G5 is more fully out-of-order, and can find the parallelism
* by itself. The big limit is that it has a 2-cycle ALU latency, so
* even though it's 2-way, the code has to be scheduled as if it's
* 4-way, which can be a limit. To help it, we try to schedule the
* read of RA(t) as late as possible so it doesn't stall waiting for
* the previous round's RE(t-1), and we try to rotate RB(t) as early
* as possible while reading RC(t) (= RB(t-1)) as late as possible.
*/
/* the initial loads. */
#define LOADW(s) \
lwz W(s),(s)*4(%r4)
/*
* Perform a step with F0, and load W(s). Uses W(s) as a temporary
* before loading it.
* This is actually 10 instructions, which is an awkward fit.
* It can execute grouped as listed, or delayed one instruction.
* (If delayed two instructions, there is a stall before the start of the
* second line.) Thus, two iterations take 7 cycles, 3.5 cycles per round.
*/
#define STEPD0_LOAD(t,s) \
add RE(t),RE(t),W(t); andc %r0,RD(t),RB(t); and W(s),RC(t),RB(t); \
add RE(t),RE(t),%r0; rotlwi %r0,RA(t),5; rotlwi RB(t),RB(t),30; \
add RE(t),RE(t),W(s); add %r0,%r0,%r5; lwz W(s),(s)*4(%r4); \
add RE(t),RE(t),%r0
/*
* This is likewise awkward, 13 instructions. However, it can also
* execute starting with 2 out of 3 possible moduli, so it does 2 rounds
* in 9 cycles, 4.5 cycles/round.
*/
#define STEPD0_UPDATE(t,s,loadk...) \
add RE(t),RE(t),W(t); andc %r0,RD(t),RB(t); xor W(s),W((s)-16),W((s)-3); \
add RE(t),RE(t),%r0; and %r0,RC(t),RB(t); xor W(s),W(s),W((s)-8); \
add RE(t),RE(t),%r0; rotlwi %r0,RA(t),5; xor W(s),W(s),W((s)-14); \
add RE(t),RE(t),%r5; loadk; rotlwi RB(t),RB(t),30; rotlwi W(s),W(s),1; \
add RE(t),RE(t),%r0
/* Nicely optimal. Conveniently, also the most common. */
#define STEPD1_UPDATE(t,s,loadk...) \
add RE(t),RE(t),W(t); xor %r0,RD(t),RB(t); xor W(s),W((s)-16),W((s)-3); \
add RE(t),RE(t),%r5; loadk; xor %r0,%r0,RC(t); xor W(s),W(s),W((s)-8); \
add RE(t),RE(t),%r0; rotlwi %r0,RA(t),5; xor W(s),W(s),W((s)-14); \
add RE(t),RE(t),%r0; rotlwi RB(t),RB(t),30; rotlwi W(s),W(s),1
/*
* The naked version, no UPDATE, for the last 4 rounds. 3 cycles per.
* We could use W(s) as a temp register, but we don't need it.
*/
#define STEPD1(t) \
add RE(t),RE(t),W(t); xor %r0,RD(t),RB(t); \
rotlwi RB(t),RB(t),30; add RE(t),RE(t),%r5; xor %r0,%r0,RC(t); \
add RE(t),RE(t),%r0; rotlwi %r0,RA(t),5; /* spare slot */ \
add RE(t),RE(t),%r0
/*
* 14 instructions, 5 cycles per. The majority function is a bit
* awkward to compute. This can execute with a 1-instruction delay,
* but it causes a 2-instruction delay, which triggers a stall.
*/
#define STEPD2_UPDATE(t,s,loadk...) \
add RE(t),RE(t),W(t); and %r0,RD(t),RB(t); xor W(s),W((s)-16),W((s)-3); \
add RE(t),RE(t),%r0; xor %r0,RD(t),RB(t); xor W(s),W(s),W((s)-8); \
add RE(t),RE(t),%r5; loadk; and %r0,%r0,RC(t); xor W(s),W(s),W((s)-14); \
add RE(t),RE(t),%r0; rotlwi %r0,RA(t),5; rotlwi W(s),W(s),1; \
add RE(t),RE(t),%r0; rotlwi RB(t),RB(t),30
#define STEP0_LOAD4(t,s) \
STEPD0_LOAD(t,s); \
STEPD0_LOAD((t+1),(s)+1); \
STEPD0_LOAD((t)+2,(s)+2); \
STEPD0_LOAD((t)+3,(s)+3)
#define STEPUP4(fn, t, s, loadk...) \
STEP##fn##_UPDATE(t,s,); \
STEP##fn##_UPDATE((t)+1,(s)+1,); \
STEP##fn##_UPDATE((t)+2,(s)+2,); \
STEP##fn##_UPDATE((t)+3,(s)+3,loadk)
#define STEPUP20(fn, t, s, loadk...) \
STEPUP4(fn, t, s,); \
STEPUP4(fn, (t)+4, (s)+4,); \
STEPUP4(fn, (t)+8, (s)+8,); \
STEPUP4(fn, (t)+12, (s)+12,); \
STEPUP4(fn, (t)+16, (s)+16, loadk)
.globl ppc_sha1_core
ppc_sha1_core:
stwu %r1,-80(%r1)
stmw %r13,4(%r1)
/* Load up A - E */
lmw %r27,0(%r3)
mtctr %r5
1:
LOADW(0)
lis %r5,0x5a82
mr RE(0),%r31
LOADW(1)
mr RD(0),%r30
mr RC(0),%r29
LOADW(2)
ori %r5,%r5,0x7999 /* K0-19 */
mr RB(0),%r28
LOADW(3)
mr RA(0),%r27
STEP0_LOAD4(0, 4)
STEP0_LOAD4(4, 8)
STEP0_LOAD4(8, 12)
STEPUP4(D0, 12, 16,)
STEPUP4(D0, 16, 20, lis %r5,0x6ed9)
ori %r5,%r5,0xeba1 /* K20-39 */
STEPUP20(D1, 20, 24, lis %r5,0x8f1b)
ori %r5,%r5,0xbcdc /* K40-59 */
STEPUP20(D2, 40, 44, lis %r5,0xca62)
ori %r5,%r5,0xc1d6 /* K60-79 */
STEPUP4(D1, 60, 64,)
STEPUP4(D1, 64, 68,)
STEPUP4(D1, 68, 72,)
STEPUP4(D1, 72, 76,)
addi %r4,%r4,64
STEPD1(76)
STEPD1(77)
STEPD1(78)
STEPD1(79)
/* Add results to original values */
add %r31,%r31,RE(0)
add %r30,%r30,RD(0)
add %r29,%r29,RC(0)
add %r28,%r28,RB(0)
add %r27,%r27,RA(0)
bdnz 1b
/* Save final hash, restore registers, and return */
stmw %r27,0(%r3)
lmw %r13,4(%r1)
addi %r1,%r1,80
blr