在 2018年04月09日 17:40, Petr Tesarik 写道:
> Essentially, the estimated remaining time is calculated as:
>
> elapsed * (100 - progress) / progress
>
> However, print_progress() is also called when progress is 0. The
> result of a floating point division by zero is either NaN (if
> elapsed is zero), or infinity (if the system clock happens to cross
> a second's boundary since reading the start timestamp).
>
> The C standard defines only conversion of floating point values
> within the range of the destination integer variable. This means
> that conversion of NaN or infinity to an integer is undefined
> behaviour. Yes, it happens to produce INT_MIN with GCC on major
> platforms...
>
> This bug has gone unnoticed, because the very first call to
> print_progress() does not specify a start timestamp (so it cannot
> trigger the bug), and all subsequent calls are rate-limited to one
> per second. As a result, the bug is triggered very rarely.
>
> Before commit e5f96e79d69a1d295f19130da00ec6514d28a8ae, the bug also
> caused a buffer overflow. The buffer overflow is mitigated thanks to
> using snprintf() instead of sprintf(), but the program may still
> invoke undefined behaviour.
>
> Note that all other changes in the above-mentioned commit were
> ineffective. They merely reduced the precision of the calculation:
> Why would you add delta.tv_usec as a fraction if the fractional part
> is immediately truncated by a converstion to int64_t?
>
> Additionally, when the original bug is hit, the output is still
> incorrect, e.g. on my system I get:
>
> Copying data : [ 0.0 %] / eta: -9223372036854775808s
>
> For that reason, let me revert the changes from commit
> e5f96e79d69a1d295f19130da00ec6514d28a8ae and fix the bug properly,
> i.e. do not calculate ETA if progress is 0.
>
> Last but not least, part of the issue was probably caused by the
> wrong assumption that integers < 100 can be interpreted with max 3
> ASCII characters, but that's not true for signed integers. To make
> eta_to_human_short() a bit safer, use an unsigned integer type.
> > Signed-off-by: Petr Tesarik <ptesarik@xxxxxxxx>
Hi, Petr
It is good that checks the value of "current".
The previous patch resolved system crash in exceptional case. The calculation
result of "calc_delta" may be very large number or even a negative number when
making the time jump very great. In this case, it is not enough for "unsigned
integer type" and double. The struct timeval has two 64bit variables in x86 64.
Thanks.
Lianbo
> ---
> print_info.c | 23 +++++++++--------------
> 1 file changed, 9 insertions(+), 14 deletions(-)
>
> diff --git a/print_info.c b/print_info.c
> index 09e215a..ed701ab 100644
> --- a/print_info.c
> +++ b/print_info.c
> @@ -16,8 +16,6 @@
> #include "print_info.h"
> #include <time.h>
> #include <string.h>
> -#include <stdint.h>
> -#include <inttypes.h>
>
> #define PROGRESS_MAXLEN "50"
>
> @@ -354,21 +352,18 @@ static void calc_delta(struct timeval *tv_start, struct timeval *delta)
> }
>
> /* produce less than 12 bytes on msg */
> -static int eta_to_human_short (int64_t secs, char* msg, int maxsize)
> +static int eta_to_human_short (unsigned secs, char* msg)
> {
> strcpy(msg, "eta: ");
> msg += strlen("eta: ");
> if (secs < 100)
> - snprintf(msg, maxsize, "%"PRId64"s", secs);
> + sprintf(msg, "%us", secs);
> else if (secs < 100 * 60)
> - snprintf(msg, maxsize, "%"PRId64"m""%"PRId64"s",
> - secs / 60, secs % 60);
> + sprintf(msg, "%um%us", secs / 60, secs % 60);
> else if (secs < 48 * 3600)
> - snprintf(msg, maxsize, "%"PRId64"h""%"PRId64"m",
> - secs / 3600, (secs / 60) % 60);
> + sprintf(msg, "%uh%um", secs / 3600, (secs / 60) % 60);
> else if (secs < 100 * 86400)
> - snprintf(msg, maxsize, "%"PRId64"d""%"PRId64"h",
> - secs / 86400, (secs / 3600) % 24);
> + sprintf(msg, "%ud%uh", secs / 86400, (secs / 3600) % 24);
> else
> sprintf(msg, ">2day");
> return 0;
> @@ -384,8 +379,8 @@ print_progress(const char *msg, unsigned long current, unsigned long end, struct
> static unsigned int lapse = 0;
> static const char *spinner = "/|\\-";
> struct timeval delta;
> - int64_t eta;
> - char eta_msg[32] = " ";
> + double eta;
> + char eta_msg[16] = " ";
>
> if (current < end) {
> tm = time(NULL);
> @@ -396,11 +391,11 @@ print_progress(const char *msg, unsigned long current, unsigned long end, struct
> } else
> progress = 100;
>
> - if (start != NULL) {
> + if (start != NULL && current != 0) {
> calc_delta(start, &delta);
> eta = delta.tv_sec + delta.tv_usec / 1e6;
> eta = (100 - progress) * eta / progress;
> - eta_to_human_short(eta, eta_msg, sizeof(eta_msg));
> + eta_to_human_short(eta, eta_msg);
> }
> if (flag_ignore_r_char) {
> PROGRESS_MSG("%-" PROGRESS_MAXLEN "s: [%5.1f %%] %c %16s\n",
>
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