| Message ID | 20170812104710.13543-1-colin.king@canonical.com |
|---|---|
| State | Accepted |
| Headers | show |
On 2017-08-12 03:47 AM, Colin King wrote: > From: Colin Ian King <colin.king@canonical.com> > > Being totally paranoid here, but I'd like to really ensure > data is always being read by forcing a prefetch on each data item > being read and force the compiler to never optimize this out by > stashing the read data into a circular buffer. Smarter compilers > on some arches were optimizing out the original reads; I think > this change will really force reads. > > Signed-off-by: Colin Ian King <colin.king@canonical.com> > --- > src/lib/src/fwts_safe_mem.c | 15 +++++++++++---- > 1 file changed, 11 insertions(+), 4 deletions(-) > > diff --git a/src/lib/src/fwts_safe_mem.c b/src/lib/src/fwts_safe_mem.c > index 1feb1ff2..f3f639b1 100644 > --- a/src/lib/src/fwts_safe_mem.c > +++ b/src/lib/src/fwts_safe_mem.c > @@ -68,8 +68,10 @@ int OPTIMIZE0 fwts_safe_memcpy(void *dst, const void *src, const size_t n) > */ > int OPTIMIZE0 fwts_safe_memread(const void *src, const size_t n) > { > - const volatile uint8_t *ptr = src; > - const volatile uint8_t *end = ptr + n; > + static uint8_t buffer[256]; > + const uint8_t *ptr, *end = src + n; > + uint8_t *bufptr; > + const uint8_t *bufend = buffer + sizeof(buffer); > > if (sigsetjmp(jmpbuf, 1) != 0) > return FWTS_ERROR; > @@ -77,8 +79,13 @@ int OPTIMIZE0 fwts_safe_memread(const void *src, const size_t n) > fwts_sig_handler_set(SIGSEGV, sig_handler, &old_segv_action); > fwts_sig_handler_set(SIGBUS, sig_handler, &old_bus_action); > > - while (ptr < end) > - (void)*(ptr++); > + for (bufptr = buffer, ptr = src; ptr < end; ptr++) { > + /* Force data to be read */ > + __builtin_prefetch(ptr, 0, 3); > + *bufptr = *ptr; > + bufptr++; > + bufptr = (bufptr >= bufend) ? buffer : bufptr; > + } > > fwts_sig_handler_restore(SIGSEGV, &old_segv_action); > fwts_sig_handler_restore(SIGBUS, &old_bus_action); > Acked-by: Alex Hung <alex.hung@canonical.com>
On 12 August 2017 at 16:17, Colin King <colin.king@canonical.com> wrote: > From: Colin Ian King <colin.king@canonical.com> > > Being totally paranoid here, but I'd like to really ensure > data is always being read by forcing a prefetch on each data item > being read and force the compiler to never optimize this out by > stashing the read data into a circular buffer. Smarter compilers > on some arches were optimizing out the original reads; I think > this change will really force reads. > > Signed-off-by: Colin Ian King <colin.king@canonical.com> > --- > src/lib/src/fwts_safe_mem.c | 15 +++++++++++---- > 1 file changed, 11 insertions(+), 4 deletions(-) > > diff --git a/src/lib/src/fwts_safe_mem.c b/src/lib/src/fwts_safe_mem.c > index 1feb1ff2..f3f639b1 100644 > --- a/src/lib/src/fwts_safe_mem.c > +++ b/src/lib/src/fwts_safe_mem.c > @@ -68,8 +68,10 @@ int OPTIMIZE0 fwts_safe_memcpy(void *dst, const void > *src, const size_t n) > */ > int OPTIMIZE0 fwts_safe_memread(const void *src, const size_t n) > { > - const volatile uint8_t *ptr = src; > - const volatile uint8_t *end = ptr + n; > + static uint8_t buffer[256]; > + const uint8_t *ptr, *end = src + n; > + uint8_t *bufptr; > + const uint8_t *bufend = buffer + sizeof(buffer); > > if (sigsetjmp(jmpbuf, 1) != 0) > return FWTS_ERROR; > @@ -77,8 +79,13 @@ int OPTIMIZE0 fwts_safe_memread(const void *src, const > size_t n) > fwts_sig_handler_set(SIGSEGV, sig_handler, &old_segv_action); > fwts_sig_handler_set(SIGBUS, sig_handler, &old_bus_action); > > - while (ptr < end) > - (void)*(ptr++); > + for (bufptr = buffer, ptr = src; ptr < end; ptr++) { > + /* Force data to be read */ > + __builtin_prefetch(ptr, 0, 3); > + *bufptr = *ptr; > + bufptr++; > + bufptr = (bufptr >= bufend) ? buffer : bufptr; > + } > > fwts_sig_handler_restore(SIGSEGV, &old_segv_action); > fwts_sig_handler_restore(SIGBUS, &old_bus_action); > -- > 2.11.0 > Thanks for the patch. Just back from long week-end. Acked-By/Tested-By: Naresh Bhat <naresh.bhat@linaro.org>
On 08/12/2017 06:47 PM, Colin King wrote: > From: Colin Ian King <colin.king@canonical.com> > > Being totally paranoid here, but I'd like to really ensure > data is always being read by forcing a prefetch on each data item > being read and force the compiler to never optimize this out by > stashing the read data into a circular buffer. Smarter compilers > on some arches were optimizing out the original reads; I think > this change will really force reads. > > Signed-off-by: Colin Ian King <colin.king@canonical.com> > --- > src/lib/src/fwts_safe_mem.c | 15 +++++++++++---- > 1 file changed, 11 insertions(+), 4 deletions(-) > > diff --git a/src/lib/src/fwts_safe_mem.c b/src/lib/src/fwts_safe_mem.c > index 1feb1ff2..f3f639b1 100644 > --- a/src/lib/src/fwts_safe_mem.c > +++ b/src/lib/src/fwts_safe_mem.c > @@ -68,8 +68,10 @@ int OPTIMIZE0 fwts_safe_memcpy(void *dst, const void *src, const size_t n) > */ > int OPTIMIZE0 fwts_safe_memread(const void *src, const size_t n) > { > - const volatile uint8_t *ptr = src; > - const volatile uint8_t *end = ptr + n; > + static uint8_t buffer[256]; > + const uint8_t *ptr, *end = src + n; > + uint8_t *bufptr; > + const uint8_t *bufend = buffer + sizeof(buffer); > > if (sigsetjmp(jmpbuf, 1) != 0) > return FWTS_ERROR; > @@ -77,8 +79,13 @@ int OPTIMIZE0 fwts_safe_memread(const void *src, const size_t n) > fwts_sig_handler_set(SIGSEGV, sig_handler, &old_segv_action); > fwts_sig_handler_set(SIGBUS, sig_handler, &old_bus_action); > > - while (ptr < end) > - (void)*(ptr++); > + for (bufptr = buffer, ptr = src; ptr < end; ptr++) { > + /* Force data to be read */ > + __builtin_prefetch(ptr, 0, 3); > + *bufptr = *ptr; > + bufptr++; > + bufptr = (bufptr >= bufend) ? buffer : bufptr; > + } > > fwts_sig_handler_restore(SIGSEGV, &old_segv_action); > fwts_sig_handler_restore(SIGBUS, &old_bus_action); > Acked-by: Ivan Hu <ivan.hu@canonical.com>
diff --git a/src/lib/src/fwts_safe_mem.c b/src/lib/src/fwts_safe_mem.c index 1feb1ff2..f3f639b1 100644 --- a/src/lib/src/fwts_safe_mem.c +++ b/src/lib/src/fwts_safe_mem.c @@ -68,8 +68,10 @@ int OPTIMIZE0 fwts_safe_memcpy(void *dst, const void *src, const size_t n) */ int OPTIMIZE0 fwts_safe_memread(const void *src, const size_t n) { - const volatile uint8_t *ptr = src; - const volatile uint8_t *end = ptr + n; + static uint8_t buffer[256]; + const uint8_t *ptr, *end = src + n; + uint8_t *bufptr; + const uint8_t *bufend = buffer + sizeof(buffer); if (sigsetjmp(jmpbuf, 1) != 0) return FWTS_ERROR; @@ -77,8 +79,13 @@ int OPTIMIZE0 fwts_safe_memread(const void *src, const size_t n) fwts_sig_handler_set(SIGSEGV, sig_handler, &old_segv_action); fwts_sig_handler_set(SIGBUS, sig_handler, &old_bus_action); - while (ptr < end) - (void)*(ptr++); + for (bufptr = buffer, ptr = src; ptr < end; ptr++) { + /* Force data to be read */ + __builtin_prefetch(ptr, 0, 3); + *bufptr = *ptr; + bufptr++; + bufptr = (bufptr >= bufend) ? buffer : bufptr; + } fwts_sig_handler_restore(SIGSEGV, &old_segv_action); fwts_sig_handler_restore(SIGBUS, &old_bus_action);