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Memcheck: handle origin data for 8-/16-bit shadow stores a bit more accurately.

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With origin tracking enabled, 8- and 16-bit stores could sometimes lose origin
info unnecessarily.  This patch removes this avoidable lossage.  (Since MC
only stores 1 origin value for each 32-bit word of address space, there is
still unavoidable lossage of origins in some cases; this patch does not help
in those cases since it's a fundamental design limitation.)
This commit is contained in:
Julian Seward 2023-01-04 16:32:03 +01:00
parent fa3a9cc43c
commit d99a6f70e2
1 changed files with 36 additions and 0 deletions
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36
memcheck/mc_main.c
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@ -79,6 +79,10 @@ static void ocache_sarp_Clear_Origins ( Addr, UWord ); /* fwds */
paths */
#define OC_ENABLE_ASSERTIONS 0
/* Change this to 1 for experimental, higher precision origin tracking
8- and 16-bit store handling. */
#define OC_PRECISION_STORE 1
/*------------------------------------------------------------*/
/*--- Comments on the origin tracking implementation ---*/
@ -7655,12 +7659,31 @@ void VG_REGPARM(2) MC_(helperc_b_store1)( Addr a, UWord d32 ) {
line = find_OCacheLine( a );
#if OC_PRECISION_STORE
if (LIKELY(d32 == 0)) {
// The byte is defined. Just mark it as so in the descr and leave the w32
// unchanged. This may make the descr become zero, so the line no longer
// contains useful info, but that's OK. No loss of information.
line->u.main.descr[lineoff] &= ~(1 << byteoff);
} else if (d32 == line->u.main.w32[lineoff]) {
// At least one of the four bytes in the w32 is undefined with the same
// origin. Just extend the mask. No loss of information.
line->u.main.descr[lineoff] |= (1 << byteoff);
} else {
// Here, we have a conflict: at least one byte in the group is undefined
// but with some other origin. We can't represent both origins, so we
// forget about the previous origin and install this one instead.
line->u.main.descr[lineoff] = (1 << byteoff);
line->u.main.w32[lineoff] = d32;
}
#else
if (d32 == 0) {
line->u.main.descr[lineoff] &= ~(1 << byteoff);
} else {
line->u.main.descr[lineoff] |= (1 << byteoff);
line->u.main.w32[lineoff] = d32;
}
#endif
}
void VG_REGPARM(2) MC_(helperc_b_store2)( Addr a, UWord d32 ) {
@ -7683,12 +7706,25 @@ void VG_REGPARM(2) MC_(helperc_b_store2)( Addr a, UWord d32 ) {
line = find_OCacheLine( a );
#if OC_PRECISION_STORE
// Same logic as in the store1 case above.
if (LIKELY(d32 == 0)) {
line->u.main.descr[lineoff] &= ~(3 << byteoff);
} else if (d32 == line->u.main.w32[lineoff]) {
line->u.main.descr[lineoff] |= (3 << byteoff);
line->u.main.w32[lineoff] = d32;
} else {
line->u.main.descr[lineoff] = (3 << byteoff);
line->u.main.w32[lineoff] = d32;
}
#else
if (d32 == 0) {
line->u.main.descr[lineoff] &= ~(3 << byteoff);
} else {
line->u.main.descr[lineoff] |= (3 << byteoff);
line->u.main.w32[lineoff] = d32;
}
#endif
}
void VG_REGPARM(2) MC_(helperc_b_store4)( Addr a, UWord d32 ) {