accel/tcg: Avoid reading too much in load_atom_{2,4}

When load_atom_extract_al16_or_al8 is inexpensive, we want to use
it early, in order to avoid the overhead of required_atomicity.
However, we must not read past the end of the page.

If there are more than 8 bytes remaining, then both the "aligned 16"
and "aligned 8" paths align down so that the read has at least
16 bytes remaining on the page.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Richard Henderson 2023-08-10 08:37:14 -07:00
parent 64d3be986f
commit 6a2c23ddeb
3 changed files with 47 additions and 3 deletions

View File

@ -404,7 +404,10 @@ static uint16_t load_atom_2(CPUArchState *env, uintptr_t ra,
return load_atomic2(pv);
}
if (HAVE_ATOMIC128_RO) {
return load_atom_extract_al16_or_al8(pv, 2);
intptr_t left_in_page = -(pi | TARGET_PAGE_MASK);
if (likely(left_in_page > 8)) {
return load_atom_extract_al16_or_al8(pv, 2);
}
}
atmax = required_atomicity(env, pi, memop);
@ -443,7 +446,10 @@ static uint32_t load_atom_4(CPUArchState *env, uintptr_t ra,
return load_atomic4(pv);
}
if (HAVE_ATOMIC128_RO) {
return load_atom_extract_al16_or_al8(pv, 4);
intptr_t left_in_page = -(pi | TARGET_PAGE_MASK);
if (likely(left_in_page > 8)) {
return load_atom_extract_al16_or_al8(pv, 4);
}
}
atmax = required_atomicity(env, pi, memop);

View File

@ -9,7 +9,7 @@ AARCH64_SRC=$(SRC_PATH)/tests/tcg/aarch64
VPATH += $(AARCH64_SRC)
# Base architecture tests
AARCH64_TESTS=fcvt pcalign-a64
AARCH64_TESTS=fcvt pcalign-a64 lse2-fault
fcvt: LDFLAGS+=-lm

View File

@ -0,0 +1,38 @@
#include <sys/mman.h>
#include <sys/shm.h>
#include <unistd.h>
#include <stdio.h>
int main()
{
int psize = getpagesize();
int id;
void *p;
/*
* We need a shared mapping to enter CF_PARALLEL mode.
* The easiest way to get that is shmat.
*/
id = shmget(IPC_PRIVATE, 2 * psize, IPC_CREAT | 0600);
if (id < 0) {
perror("shmget");
return 2;
}
p = shmat(id, NULL, 0);
if (p == MAP_FAILED) {
perror("shmat");
return 2;
}
/* Protect the second page. */
if (mprotect(p + psize, psize, PROT_NONE) < 0) {
perror("mprotect");
return 2;
}
/*
* Load 4 bytes, 6 bytes from the end of the page.
* On success this will load 0 from the newly allocated shm.
*/
return *(int *)(p + psize - 6);
}