[ccan] [PATCH] altstack: stack alignment and accounting tweaks
Dan Good
dan at dancancode.com
Mon Feb 1 13:43:16 AEDT 2016
* add altstack_remn, returns amount of stack remaining
* increase mapping by 1 page to handle abutment case
* capture rsp earlier
* align stack to 16 bytes
Signed-off-by: Dan Good <dan at dancancode.com>
---
ccan/altstack/altstack.c | 17 ++++++++++++++---
ccan/altstack/altstack.h | 14 ++++++++++++++
ccan/altstack/test/run.c | 20 +++++++++++++-------
3 files changed, 41 insertions(+), 10 deletions(-)
diff --git a/ccan/altstack/altstack.c b/ccan/altstack/altstack.c
index 6faf38f..b71c64f 100644
--- a/ccan/altstack/altstack.c
+++ b/ccan/altstack/altstack.c
@@ -8,6 +8,7 @@
#include <signal.h>
#include <stdio.h>
#include <string.h>
+#include <unistd.h>
#include <sys/mman.h>
static __thread char ebuf[ALTSTACK_ERR_MAXLEN];
@@ -37,6 +38,11 @@ static void segvjmp(int signum)
}
static __thread void *rsp_save_[2];
+static __thread rlim_t max_;
+
+rlim_t altstack_max(void) {
+ return max_;
+}
static ptrdiff_t rsp_save(unsigned i) {
assert(i < 2);
@@ -57,6 +63,7 @@ static __thread void *arg_, *out_;
int altstack(rlim_t max, void *(*fn)(void *), void *arg, void **out)
{
+ long pgsz = sysconf(_SC_PAGESIZE);
int ret = -1, undo = 0;
char *m;
struct rlimit rl_save;
@@ -69,11 +76,16 @@ int altstack(rlim_t max, void *(*fn)(void *), void *arg, void **out)
fn_ = fn;
arg_ = arg;
out_ = 0;
+ max_ = max;
ebuf[elen = 0] = '\0';
if (out) *out = 0;
+ // if the first page below the mapping is in use, we get max-pgsz usable bytes
+ // add pgsz to max to guarantee at least max usable bytes
+ max += pgsz;
+
ok(getrlimit(RLIMIT_STACK, &rl_save), 1);
- ok(setrlimit(RLIMIT_STACK, &(struct rlimit) { max, rl_save.rlim_max }), 1);
+ ok(setrlimit(RLIMIT_STACK, &(struct rlimit) { max_, rl_save.rlim_max }), 1);
undo++;
ok(m = mmap(0, max, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_GROWSDOWN|MAP_NORESERVE, -1, 0), 1);
@@ -91,8 +103,7 @@ int altstack(rlim_t max, void *(*fn)(void *), void *arg, void **out)
ok(sigaction(SIGSEGV, &sa, &sa_save), 1);
undo++;
- asm volatile ("movq %%rsp, %%r10\nmov %0, %%rsp\npush %%r10" : : "g" (m + max) : "r10");
- rsp_save(0);
+ asm volatile ("movq %%rsp, %%r10\nmov %1, %%rsp\nmov %%rsp, %0\nsub $8, %%rsp\npush %%r10" : "=g" (rsp_save_[0]) : "g" (m + max) : "r10");
out_ = fn_(arg_);
asm volatile ("pop %rsp");
ret = 0;
diff --git a/ccan/altstack/altstack.h b/ccan/altstack/altstack.h
index 5570e7b..4445a2a 100644
--- a/ccan/altstack/altstack.h
+++ b/ccan/altstack/altstack.h
@@ -104,6 +104,20 @@ char *altstack_geterr(void);
ptrdiff_t altstack_used(void);
/**
+ * altstack_max - return usable stack size
+ *
+ * Returns: max value from altstack() call
+ */
+rlim_t altstack_max(void);
+
+/**
+ * altstack_remn - return amount of stack remaining
+ *
+ * Returns: altstack_max() minus altstack_used()
+ */
+#define altstack_remn() (altstack_max() - altstack_used())
+
+/**
* altstack_rsp_save - set initial rsp value
*
* Capture the current value of rsp for future altstack_used()
diff --git a/ccan/altstack/test/run.c b/ccan/altstack/test/run.c
index adc1020..d0b8d28 100644
--- a/ccan/altstack/test/run.c
+++ b/ccan/altstack/test/run.c
@@ -4,6 +4,7 @@
#include <setjmp.h>
#include <signal.h>
#include <string.h>
+#include <unistd.h>
#include <sys/mman.h>
#include <ccan/tap/tap.h>
#include <ccan/altstack/altstack.h>
@@ -20,13 +21,13 @@ enum {
};
int fail, call1, call2;
char *m_;
-rlim_t max_;
+rlim_t msz_;
#define e(x) (900+(x))
#define seterr(x) (errno = e(x))
#define setcall(x) ((call1 |= !errno ? (x) : 0), (call2 |= errno || out_ ? (x) : 0))
#define getrlimit(...) (fail&getrlimit_ ? (seterr(getrlimit_), -1) : (setcall(getrlimit_), getrlimit(__VA_ARGS__)))
#define mmap(...) (fail&mmap_ ? (seterr(mmap_), (void *)-1) : (setcall(mmap_), mmap(__VA_ARGS__)))
-#define munmap(a, b) (fail&munmap_ ? (seterr(munmap_), -1) : (setcall(munmap_), munmap(m_=(a), max_=(b))))
+#define munmap(a, b) (fail&munmap_ ? (seterr(munmap_), -1) : (setcall(munmap_), munmap(m_=(a), msz_=(b))))
#define setrlimit(...) (fail&setrlimit_ ? (seterr(setrlimit_), -1) : (setcall(setrlimit_), setrlimit(__VA_ARGS__)))
#define sigaltstack(...) (fail&sigaltstack_ ? (seterr(sigaltstack_), -1) : (setcall(sigaltstack_), sigaltstack(__VA_ARGS__)))
#define sigaction(...) (fail&sigaction_ ? (seterr(sigaction_), -1) : (setcall(sigaction_), sigaction(__VA_ARGS__)))
@@ -58,7 +59,9 @@ static void *wrap(void *i)
int main(void)
{
- plan_tests(16);
+ long pgsz = sysconf(_SC_PAGESIZE);
+
+ plan_tests(17);
#define chkfail(x, y, z, c1, c2) (call1 = 0, call2 = 0, errno = 0, ok1((fail = x) && (y) && errno == (z) && call1 == (c1) && call2 == (c2)));
#define chkok( y, z, c1, c2) (call1 = 0, call2 = 0, errno = 0, fail = 0, ok1((y) && errno == (z) && call1 == (c1) && call2 == (c2)));
@@ -86,7 +89,7 @@ int main(void)
chkfail(munmap_, altstack(8*MiB, wrap, 0, 0) == 1, e(munmap_),
getrlimit_|setrlimit_|mmap_|sigaltstack_|sigaction_,
setrlimit_|sigaltstack_|sigaction_);
- if (fail = 0, munmap(m_, max_) == -1)
+ if (fail = 0, munmap(m_, msz_) == -1)
err(1, "munmap");
chkok( altstack(1*MiB, wrap, (void *) 1000000, 0) == -1, EOVERFLOW,
@@ -102,10 +105,12 @@ int main(void)
chkfail(munmap_, altstack(1*MiB, wrap, (void *) 1000000, 0) == -1, EOVERFLOW,
getrlimit_|setrlimit_|mmap_|sigaltstack_|sigaction_,
setrlimit_|sigaltstack_|sigaction_);
- if (fail = 0, munmap(m_, max_) == -1)
+ if (fail = 0, munmap(m_, msz_) == -1)
err(1, "munmap");
- ok1(used > 1*MiB-1*KiB && used < 1*MiB);
+ ok1(altstack_max() == 1*MiB);
+ diag("used: %lu", used);
+ ok1(used >= 1*MiB && used <= 1*MiB + pgsz);
char *p;
for(p = altstack_geterr(); *p; p++)
@@ -128,7 +133,8 @@ int main(void)
getrlimit_|setrlimit_|mmap_|sigaltstack_|sigaction_,
setrlimit_|munmap_|sigaltstack_|sigaction_);
- ok1(used > 8*MiB-8*KiB && used < 8*MiB);
+ diag("used: %lu", used);
+ ok1(used >= 8*MiB && used <= 8*MiB + pgsz);
used = 0;
chkok( altstack(8*MiB, wrap, (void *) 100000, 0) == 0, 0,
--
2.4.3
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